Adam's Cherub Hull Build 2010

Self-tacker design

2011-02-15T14:18:00.006+11:00

To work out the radius of the self-tacker track i started with working out what i wanted from it as follows:

The leech tension to remain the same on all positions of the track: This was so that i could adjust the car position without having to adjust the jib sheet as well, so that simple tweaks could be made.
The foot remains that same tension on all positions of the track: This was to keep the foot tension on the jib an independent variable from the outward position of the car. I adjust the foot tension by the position of the jib sheet on the clew board.

Some people like to set the boat up so that the leech tension decreases as the car is eased or have the foot tension increase as the car goes out. I'm personally not a fan of this as you are effecting two parameters with one variable and i feel you could end up in a position that you need to constantly tweak two controls just to setup the one parameter you want to vary.

If order for these criteria to be meet the jib car will need to follow the jib clew as it moves exactly. To do this it means the distance from the head to the jib car must remain the same as it travels. Secondly the distance from the tack to the car must also remain the same. This gives us the simple problem where we have a triangle with constant length sides that pivots about the forestay.

Therefore it can be found quite easily. Either by the geometry of the jib and then find the line length that runs through the clew and is perpendicular to the forestay. Or once the boat is rigged up you could just use a tape measure and builders square to find the distance perpendicular to the forestay.

The only other things you need to consider is to account for the fact you self tacker track will sit something like 30mm above the deck at the centreline and to allow for pulley's etc.

Also if the track has a slightly smaller radius than needed the sheet tension will increase slightly as it passes the centreline during a tack. If the track is on a slighlty larger radius then the sheet will loosen slightly during the tack. I personally favour the track to be on a slightly larger radius as i don't want the sheet to tighten up and jam during a tack.

From memory my current track is a 1580mm radius

Self-tacker track construction

2011-02-14T20:45:00.005+11:00

In order to fit a self-tacking jib to the boat i needed a method of curving a track for the jib car to run on. On other boats i have seen this done in a couple of ways:

A ronstan I-beam (series 19) track is ordered from ronstan to be bent to a given radius, which can then just be mounted to a support at each end and a support in the middle to prevent the track from twisting or warping off its supports. (e.g. 3 mounting points that are not co-linear are the minimum required to make the mounting stable). When i investigated this the track was roughly $300, with a lead time of 3 weeks and the car cost around $170.
A thinner track like a ronstan series 14 BB track or a Harken Micro CB track is flexed to a rigid backing or a series of brackets attached to the deck.
The track as above is directly attached to a concave deck that matches the curvature of the track.

I chose to use a rigid backing support that i could then force the bend in the track as it was bolted to the support.

To make the support i screwed two pieces of 18mm form ply together giving a piece of timber 36mm thick. Next the required radius was traced using a pencil and piece of string. This was then cut out carefully with a jigsaw and neatened up with a belt sander. To give a radius on the edge a quarter round radius bit was used in a router (with a ball bearing).

This mould was then covered in packaging tape as a mould release and two strips of 10mm foam where cut to cover the mould.

The laminate is described in the image below. First the two layers of glass are laminated onto the mould surface with a +-45 degree orientation to the length of the mould. Next two layers of 300gsm UD carbon that is only wide enough to cover the flat surface are laminated. If the strips are wider they will not stick to the sides of the mould.

There are several reasons for laminating the glass on the -+45 deg (or carbon if you wish, i would still use two layers ontop and atleast 1 on the bottom).

When the fabric is on the -+45 deg it wraps very easily around the corners of the mould and also traces the curved radius of the track well. Otherwise you need to place cuts all the way along the edge if the fabric is on the 0/90 deg
When this beam is in bending the one outside skin will be in tension while the other is in compression. If there were no skins on the side the foam core would need to carry a shear load between the two outside skins. Since foam has a low shear modulus (stiffness) the will deflect significantly. Since woven fabrics have there highest shear modulus and strength when the fibres are on a -+45 deg it is a good idea to place these skins on the side as it will give you a stiffer and stronger beam.
Unidirectional composites are generally stronger in tension than in compression because when the fibres are under compression the individual fibres tend to buckle. In order to improve this compressive strength a laminate on the -+45 deg to the unidirectional fibres should be used. This is because the cloth layer on top allows the load to be passed from one fibre the neighbouring fibre through a shear stress which is taken by the woven fabric. I'm fairly sure that i read somewhere this can improve the compressive strength by 10-15%.

Next spread a runny bog of Q-cells and epoxy resin onto all surfaces of the foam and place them on top of the laminate. Then continue to laminate the rest. Once the peel ply is placed over the top carefully place strips of packaging tape over the laminate starting in the centre and working towards the ends.

Once cured it can be easily trimmed to length and the track is bolted to the support. Care needs to be taken when clamping the track to the support. If you place a clamp in the centre and tighten it up you will buckle the track and place a bump in the track, which can stop the car from moving.

Bowsprite idea

2011-02-14T14:39:00.005+11:00

Also thought i would mention this,

Trev Fay pointed it out to me at the nationals in Adelaide mentioning it was one of the best solutions for it he has seen. I can't remember which boat was using it, though i think it is a very elegant solution to the problem.

When setting up the tip of the bowsprite you want it to do a couple of things;

1. Be able to get the spinnaker tack as far forward as possible, as the bowsprite is limited in length.
2. Be a low friction setup for the strop to move through
3. Lightweight, since it is at the extremity of the boat hull e.g. effects the rotational inertia of the hull to pitching and turning.

I normally use two sheave boxes, which cost about $20 each and you need to reinforce the tip of bowsprite as you cut most of the material away to fit the sheave boxes.

The idea used on this boat i saw used a turned plastic plug in the pole tip with a hole straight through the tip. The ends of the hole where nicely rounded to avoid chaffing the rope and the plug was made from a nylon or low friction plastic.

I image this could be made to be very light weight if the inside of the plug was hollowed out.

Vang Design

2011-02-14T12:47:00.007+11:00

I first saw the lever style vang on a forum after a 12 ft skiff had trialled the setup. Shortly after i saw it on some international 14's. The advantages that i saw immediately were the increase in cockpit space for the crew over a conventional vang system and (for my boat particularly) the clearance for the centreboard to be raised downwind.

Image 1: 12ft skiff design, i think it was built around 2006
Image 2: i14 design, possibly built around 2003
Images from (http://forums.sailinganarchy.com/index.php?showtopic=31443)

I began to look at this design concept for my older boat "Heart Shaped Box" and began a basic force analysis to compare a conventional setup to a lever style and the loads involved. This was fairly basic and going over it now i can see that there are several errors but i believe it represents a reasonable comparison between the two systems. The assumptions that i made were a 50kg load along the leech of the main sail and i only considered the lever vang forces parallel to the boom (not accounting for misalignment, which I'll explain later)

The results of this analysis was that an axial load on the purchase system needed for each system was as follows at 50kg of leech load.

Conventional = 1805 N (184 kg)
Lever = 1345 N (137 kg)

This gives a 25% reduction in the load at the rope. Meaning that where a 16:1 purchase was used before a 12:1 system could now be used for the same power. Having less purchase means less excess rope in the boat when the vang is sheeted on hard giving less rope to tangle in the boat.

While i was looking at this system a cherub at Lane Cove 12ft skiff club "Ajax" trialed the lever vang systems as they had played with the system on a 12ft skiff. After discussing with them to mentioned that you need to be wary of the sheeting angle at the tip of the lever as it can place a vertical load on the goose neck and this needs to be understood to make sure it isn't neglected.

To understand this lifting force you need to see that the boom/lever member is pivoting about the goose neck and the point which you are applying to load is the end of the lever. When this system is pivoting the tip of the lever will trace an arc with the centre point being the goose neck. If the load at the tip of the lever isn't applied tangent to this arc then the force can be broken into a vertical and a horizontal force. As this misalignment gets larger the vertical component starts to grow, but is still fairly small.

The next this i looked at the was the clearance on the centreboard as on my older boat the centre case was fairly close to the mast meaning that there was not a lot of room between the vang and centreboard. It showed i could get a significant increase in the clearance.

When it came to fitting out my new boat i looked at how i would actually set up the system. In order for the vang to work properly the leech tension should remain the same as the boom is eased through its travel. Since the boom is pivoted about the goose neck if the ropes on the end of the lever is pivoted about a similar position on the mast then the leech tension should remain the same. I was first concerned about the bending this would place on the lower mast and how this would effect the mast bend further up the rig. So i looked at options for having the pulley systems attached to the hull rather than the mast. The image below shows different loci that i had traced from different ways of wrapping the ropes around the mast to approximate an arc from the mast. The blue lines show that the system followed an arc about the centre of the mast until one of the ropes stopped touching the side of the mast, at which point it started tracing an ellipse from the pulley on the hull and the mast. I felt that this would approximate the arc enough to be a practical system.

These images below show the setup that i used. The lever was made from carbon over a polystyrene foam core with a section of windsurfer mast as the main structure inside. This was don't to make it as stiff as possible as flex in the boom or lever results in a loss of leech tension when the boom moves from dead centre to slightly eased as the pulley's at the boom tip stop taking the vertical load of the leech.

The purchase i went with was a 3:1 followed by a 2:1 around the mast, giving a 6:1 all up on the lever tip. Although this was lower than first calculated it was decided to try it as the old vang system was rather easy.

Conclusions:
After sailing with this setup for a little while now there are several changes I plan to make. First of all, we are struggling to get the height out of the boat that others have and I'm starting to feel that this is due to the leech on our mainsail. The vang is slightly underpowered meaning that in the stronger breezes it is hard to get a good trim on the leech.

Secondly the way the vang wraps around the mast gives some deviation from an arc so i will move the pickup point to the back of the mast. As a small deviation at the lever tip is multiplied by four at the tip of boom (ratio of lengths) so 2 mm at the lever = 8 mm at boom tip, which will reduce the leech tension quite a bit.

1. Power: I will increase the purchase of the system to 10:1 0r 12:1 from the 6:1 i originally had.

2. Pick up points and locus: i will move the pick up to the back of tha mast and if mast bend is excessive i will place a strap/strop to the hull forward of the mast.

Other than this the vang shows promise, giving good clearance to the centreboard and more room for the crew. The lever i added to my boom is on the heavy side (about 1 kg), as it was placed on the boom two days before the nationals and i didn't want it to fail. So improvements could definitely be made there.

just a few more photos

More Bulkhead Repairs

2011-02-01T20:56:00.003+11:00

After returning from the nationals we identified another small crack in the bulkhead/deck joint but this time it was much closer to the centre line of the boat. Upon closer inspection the crack occurred at the ply drop of a unidirectional layer from two layers down to one layer, yet still with a -+45 deg carbon cloth patch covering the ply drop.

The crack is clearly a compression failure and as can be seen even propagates past the carbon fibre material and into the bog covered fibreglass cloth each side.

To me this suggests that only 1 layer of carbon uni at 50mm wide is not sufficient to carry the loads running through this part of the hull. While considering that i suspected the load in this bulkhead/deck joint to diminish as the distance from the side stay increased (spreading the load into the adjacent bulkhead and deck material). This decrease is either non-existent or smaller than i anticipated. Also it is clear the failure occurred at the ply drop, which is a known stress concentration point. In future i would recommend that ply drops in a similar situation should be tapered (e.g. cut the end of the strip to become a point) as this should spread the stress concentration over a longer distance and prevent a straight line that is perpendicular to the load path being formed.

Also noted was that when i peeled up the damaged area that the epoxy did not stick particularly well the to the bog/filler that was next to the laminate e.g. from the old paint and filler. In future i think that needs to be sanded back further and more attention paid to make sure that all "stop putty" is removed with acetone before laminating.

I suspect that the reason this is happening is for two reasons, both involving the stiffness of the structure.

1. As mentioned earlier, stiffer structures generally experience higher peak shock loads as the structure deflects less when loaded (due to being stiffer) the time over which the load is applied and reacted to is reduced e.g. a shorter impact time. This gives a higher peak acceleration to the overall structure, which for a given mass gives a higher force (F=ma). Therefore a stiffer boat with stiffer rigging is going to suffer higher accelerations when slamming on waves. The next question is whether my new boat is actually any stiffer than other boats out there at the moment. I feel that i could be but its rather hard to prove or test and therefore hard to judge with this has a significant effect or not.

2. The second reason i feel this has occurred is due to the relative stiffness of the laminates used in and around the bulkhead/deck joint. Woven fibreglass cloth laminates have an elastic modulus (stiffness) which is drastically lower than carbon fibre fabric or unidirectional tapes as per below.

Young's or Elastic Modulus:

Woven E-glass (0/90 deg) = 25 GPa
Woven E-glass (-+45 deg) = 12.3 GPa
Woven Carbon (0/90 deg) = 70 GPa
Woven Carbon (-+45 deg) = 17 GPa
Uni Carbon (0 deg) = 135 GPa

Source: (http://www.performance-composites.com/carbonfibre/mechanicalproperties_2.asp) 01/02/2011

Now assuming that the E-glass fabric each side of carbon fibre strips is at 0/90 degrees then the unidirectional carbon is approx 5.5 times stiffer then the glass next to it. I feel that it is this reason that very little load is being transferred into the deck or bulkhead but instead travelling along the much stiffer carbon. This is because as the carbon compresses and strains the glass next to it strains an equal amount but because of the low stiffness it only corresponds to a low stress level and therefore contributes to very little load carry ability of the structure.

If this fibreglass is in fact not on an 0/90 degree angle the situation only gets worse until the angle reaches -+45 degrees when the stiffness difference becomes approximately 11 times...

With this now in mind i need to consider how i can make this carbon fibre laminate strong enough to solely carry the rigging loads and allow it to transfer to the fore stay without just moving the problem further along the boat.

Since the failure occurred in a single ply of unidirectional carbon yet not in the section with a double ply it would be okay to assume that this would be sufficient. Though considering this appears to be quite highly stressed and it is unlikely that the boat has experienced its highest loads that it ever will. With this in mind and also the effects of fatigue to be considered (although UD carbon has an excellent fatigue life) it would be a good idea to increase the factor of safety. Therefore i will try to locate the previous ply drops and rejoin them to give a 3 ply laminate to carry from side stay to centre line on the deck on both sides.

From here i will need to try to "dissipate" this load to the foredeck and the "V" beam underneath the deck. To do this i plan to arrange a patch or two of carbon cloth at different fibre orientations to try and spread it over a large enough area in the E-glass deck to carry the load.

Otherwise the next step would be to run carbon all the way along the deck to the fore stay mount. Though this would be rather undesirable as quite a large area would then need to be faired in and re-painted, which would be quite a major repair.

I will try to document the repair process as much as possible when i undertake it later on in the week.

Nationals

2011-02-01T17:58:00.005+11:00

The preparation for the nationals was very much a rush job considering the late completion of the boat and the fact that uni studies where pulling me a away from tuning and finishing the boat.

The rig was tested in the front yard for the bend characteristics of the mast under different leech loads using wire, digital scales and a block and tackle. A tight string was then run from tip the goose neck and measurements every 1/8th of the luff length taken. This gives useful information to the sail maker for determining the luff curve.

The data in the graph above shows the curves produced for different leech loads and lower stay positions e.g. (tight or loose). From the graph you can see that the difference between tight and loose lowers is quite substantial giving approximately 20-30mm difference in the point of max deflection and the position at which this point occurs. This data alone for me suggests that easily adjustable lowers on the water would give quite an advantage on days where the weather is quite unstable. This idea will be explored later on. Note: Data is for the 40mm ID series High modulus "Stiff" rig from CST made in late 2010.

After this it turned out that the rig performed rather closely to the older rig off Heart Shaped Box and it was therefore decided that due to the lack of time left and the close fitting of the main we would leave it as it was and not build a new one. This is certainly an area that can be improved on this boat though.

Overall the boats performance at the nationals was reasonable and certainly developed significantly at the end of the regatta, but our major downfall was lack of training/tuning and sailing in the new boat. Our sailing skills where not up to scratch, which cost us a lot of places and prevented us from getting the most from the boat. In terms of the performance of the hull, it appeared to nose dive no more or worse than the current Matthews hull design and held good pace downwind. Upwind pace was good but to combine this speed with height proved to be difficult. By the end of the regatta the boat had good upwind height and pace but it wasn't exceedingly quick, so i feel there are still plenty of improvements to be found.

Pushing the boat hard to the wind mark in a large chop and 25 knot winds

approaching the mark

Cruising along it the lighter breezes

Bulkhead repair

2011-02-01T17:31:00.004+11:00

After the sail at lane cove sailing club I noticed that there was an uneven surface that had appeared around the port side stay mount. After further investigation it turns out that strands of unidirectional fabric buckled and were poking up through the filler and paint layers. Also the plain weave fabric closer the stay mount had also buckled.

This damage was more evident on the port than the starboard side, yet since both sides were pretty much symmetrical i first thought it may have just been voids from manufacture since this area was not originally vacuum bagged.

Upon further investigation the unidirectional fabric had buckled where it did not have a covering layer of fibreglass or carbon cloth. Yet in areas the carbon fabric had also buckled in a few places. This suggested that we had underestimated the loads on the bulkhead in compression along that top surface/corner.

Yet speaking to other class builders they had mentioned that they usually just put a simple layer of carbon cloth over the corner. My laminate was two layers of glass cloth and essentially two tapes 50mm wide of uni carbon running along the corner. With carbon cloth closer to the side stay mount where the load was expected to be higher.

After further thought i concluded that if the failure was not from voids and from the boat experiencing higher loads than expected. Then it would need to be strengthened significantly since the boat had only sailed in moderate conditions. This higher load could potentially be from shock loading, as a stiffer structure will generally experience higher peak loads during shock loading when compared to a "softer" one. So at least on the positive side it my suggest that the boat is quite stiff :)

To bulk up the laminate I used 3 layers of 300 gsm uni-directional carbon 50mm wide running from the chain plate towards the centre of the boat, and tapered each layer to avoid a large laminate drop or stress concentration. Then uni strips from the ratchet blocks and possible side stay positions the meet up with the main laminate.

Then to improve the compressive strength of the unidirectional laminate a covering layer of 200gsm carbon fabric was applied at the -+ 45 deg to the uni-directional laminate. This improves the strength by allowing compressive stresses to transfer from fibre to the fibre next to each other via shear stresses through the 45 deg laminate, or to simply support and stabilise the unidirectional fibres .

The laminate was applied using the "Poor mans Pre-preg" technique and then vacuum bagged to the hull to improve consolidation and reduce void content.

2010-11-21T21:43:00.002+11:00

Update form a sail at lane cove,

The boat performed fairly well on the weekend, with the hull keeping up with the faster boats upwind and showed good downwind speed if not equal with the faster cherubs. Breeze was around 10 knots with gusts of 15. The sails were from my old boat and did not fit particularly well. Especially the spinnaker due to the further aft mast position and rake, So i needed to place strops on the tack and head to get some sort of "slack" in the luff, which produced a difficult to handle spinnaker.

With this in mind the rig has basically be placed in the boat using generic values of rake and an unknown rig tension, so I'm hoping that with some tuning and re-cutting/ new sails it will prove to be a very fast boat in medium to heavy airs.

Cost Update:

Preliminary cost of the project is as follows:

Jig materials - $550
Hull materials - $3950 (Resin, carbon, foam, consumables etc)
Power tools/ consumables - $400
Fit out - $3550 (CST rig, stays, fittings etc)

Total Cost - $8500

Although this cost is likely to be around $9000 after a few more ropes/fittings, also sails need to be considered.

I will give a more detailed cost breakdown further down the track.

2010-11-15T15:16:00.002+11:00

Well she has finally managed to get out onto the water. With a large amount of work being put in over the last couple of days she finally got a sail in.

The helm felt good but i will pay more attention to it on the next sail and try to work out if the rudder balance of mast rake/centre board position needs changing.

The boat responded well upwind when there was a decent gust, but did bog down a fair bit in the lulls. Though i think with a bit of careful fore aft trimming we will be able to solve this. The hull seems to move quit nicely through the chop while down wind it didn't seem to have some massive urge to nose dive, although we were only hiking (maybe 15-20knot gust) but it did feel quick.

The cockpit layout and rig position so forces the crew to sit further aft in the boat during tacking/gybing etc, which could lead to a problem of the transom sinking a little during tacks etc, which would mean it will be slow out of tacks.

In conclusion I'm very pleased with how the boat turned out and now my crew and I will need to focus pretty heavily on the fore-aft trim and setting up the rig position/rake to make to boat work well.

I'll let you know how she goes against some other boats hopefully next week.

Fit out has begun..

2010-11-06T21:52:00.003+11:00

Started to fit out the boat over the last couple of days with the help of the old man. Once our fittings arrived from ronstan we double check the dimensions of each fitting and its location and made a bolts list for each fitting. This resulted in several different lengths of M4 or M5 (metric) bolts being used over the whole boat in order to 1. keep weight to a minimum, 2. prevent bolts protruding into the spinnakers chute/bow pole area etc.

The bolts used were 304 grade stainless as our local store did not supply 316 grade, without ordering them in boxes of 100. So this just means that good care of the boat is needed to ensure that salt water is washed off when ever possible to minimise corrosion... on the plus side 304 is stronger than 316 grade and slightly cheaper. All up our bolt order for the bolt cost approx $100, which included several shackles and a 50 x 6mm tow ring.

All fittings on the floor and side tanks are attached to be boat by taping threads into pre-located fibreglass or carbon fibre "blocks" laminated into the floor.

The mast step is made from 2mm thick 6061-T6 aluminium, which i tig welded in the workshop at uni. The side stay and lowers mounting bracket is made from 2mm 304 stainless steel, which i also made in the workshop.

The overall rig length is 6.49m with a goose neck height of 640mm above the sheer (1000mm off the floor). I will upload a "plan/drawing" of the finalised rig once it is completed.

We roughly placed the rig into the boat this afternoon to try and estimate the stay lengths required. To do this we set the rake on the mast so that the tip was vertically above the back of the centreboard case (or equivalent distance in our case) as is a generally rule of thumb for cherub rigging. From here lengths were taken as were additional measurements of all rig fitting locations so that i can create a spreadsheet to calculation stay lengths and the effects of rake change/mast step position on length etc.

After the initial rigging today it looks like I'm going to have some "fun" trying the make the sail plan work for the boat. The jib requires a very long foot due to the mast position (6ft from the bow, as opposed to 5'6-8" or so for normal boats). I anticipated this and placed a large forestay mount on the boat allowing it to come back about 120mm, so I'll let you know what i can come up with.

2010-10-31T20:46:00.002+11:00

After many hours labour the hull as been wet & dry sanded and polished back to a smooth gloss with a few little patches showing on the side that the colour wasn't quite as thick as we once thought, but at least that means it will be light.

Since then we have finished off the cradle and put the boat back upright. The floor was then painted with white two pack paint with a roller. Three light coats were first applied wet on wet to get an even colour across the floor. To get the grippy finish a mixture of "Norglas" grip additive and caster sugar where added to the white paint. This slightly thickened mixture was then spread over the floor with a roller.

Since uni work was handed in last week its all hands on deck to get her rigged and fitted out so we can get her wet at least once before the Belmont state titles. Most of the fittings have arrived and will begin to be place on the boat mid week. A bolts order will be made early this week once we have the fittings and a new s/steel mast step is in the works to be welded up before the weekend.

Hull has been sprayed

2010-10-10T14:01:00.002+11:00

Finally got a chance to spray the hull and decks this weekend. The colour is Waratah red and flowed from the 1.4mm nozzle gun very well with no reducer. We ended up using 2.5 liters of colour (as opposed to 1.5L that i calculated from the data sheet) the main reason for this is that we decided to do a third coat on the hull from chine to chine to try and smooth out a little bit of orange peel.

Next step is to use a roller the put the white paint on floor and put in the aggregate to make a grippy finish on the floor. Then the do the final trimming pieces such as clear two pack paint on the rudder gantry, rudder, centreboard and transom bar.

Primer on topside of hull.

2010-10-04T22:46:00.004+11:00

quick update:

The hull has had a further two coats of primer and spot filler and looks pretty good if i don't say so myself. It took a lot of torture boarding and relentless sanding to get there, but i think the hull is as smooth and fair as we are going to get it. We changed over to an older spray gun we have that has a 2.0mm nozzle and we thinned the primer 15-20% with reducer and it went on a lot better than our first coat with a 1.4mm nozzle and only 10% thinner.

We had hoped to spray the hull with colour over the long weekend but the rainy weather (high humidity) has set us back. So instead we flipped the hull over and began fairing the decks and cockpit with Q-cells/ epoxy then spot filler and we gave it a coat of high build primer this afternoon.

At this stage it looks like the topside will take one more pass with some spot filler to fill a few pin holes in the side tanks and help fair in a few more joins etc. Then a final primer coat and we should be good to spray the topsides as well. Therefore potentially next weekend could be a big weekend of spraying and we might be able to get all the colour sprayed by Monday next week (weather depending).

We also reweighed the hull before adding the primer this arvo, it came in at 43.5kg, with bowsprite and rudder gantry in place. So it still looks like a may end up with some lead in the boat (touch wood!).

The new carbon rig is still a few weeks away, as are the fittings from ronstan so we have decided to skip the first round of the state titles in two weeks time. This is probably a good idea as well because uni work is starting build up for the end of October. Our next aim is to have the boat on the water by the end of October so we can get some practice in before the second round of the states in November.

Here are some images of the progress:

2010-09-26T21:25:00.002+10:00

We put the first coat of primer/ high build filler on the hull today, which went fairly well. Although we need to play with our spray gun setup and try to get more of a "Wet coat" effect as we had a fairly dry/dusty effect coming from the gun, which took quite a long time to get a decent coat over the boat. On the next coat we might try the larger nozzle size (2.0mm) as opposed to the 1.4mm size on the current setup as well as adding more than 10% thinner to the primer.

We are planing to the spray the colour next weekend.

2010-09-22T23:35:00.002+10:00

Hull laminating has been essentially completed, decks and side tanks are laminated in place as are all the hard points for fittings. At this point the hull weighed in at 41kg the minimum weight for the class is 51kg. This gives us 10kg for paint, filler and fittings.

I have worked out that i need 1.5L of (Waratah Red) colour paint for the hull, deck and side tanks and 0.25L for the white floor so i have ordered a bit more than this for wastage and spare paint in the event we need to do a significant repair down the track.

So far we have two three coats of "bog" (thickened epoxy resin with Q-cells) over the hull and "torture" boarded two of these coats and already the hull is look a lot nicer and fairer. Once we are happy with the shape or "fairness" of the hull we will spray a two part primer/filler to fill any left over small holes. Then we will be onto the final paint topcoats.

We have already ordered a new high modulus rig from CST and approx $1500 worth of pulleys, cleats and fittings from Ronstan. At this stage we are planing to be at the first state titles rounds in mid October in some form or another. Although there is still a lot of work to do associated with the centreboard case, vang system and fit out.

side tanks are in!

2010-09-11T20:53:00.005+10:00

Hi all,
Finally its starting to look like a boat!Side tanks have been glued in and laminated into place. The port tank will act as a spinnaker chute, helping to keep a clean cockpit and the stb tank will be a bouancy tank.
(this is a view down the spinnaker chute from the bow)

All of the hard points have been laminated into place, which is 5mm thick fibreglass plate, with approx 4 layers of carbon over it on the floor. These will then be drilled and tapped for an M5 or M6 bolt to attach fittings.
After re-weighing the hull with the following; sides glued in, foredeck on, gantry in the boat. The hull came in at 39.5kg which isn't bad, but i doubt that we will make the 45kg lower limit for the class (hmm that 6kg's of lead would have been good!)
This is an image of me trying to work out how to mount our vang system. The blue pen lines are a radius out from the centre of the mast, while the other lines are different layouts of connecting the system. The lay-out above with the green string appeared to follow an arc from the centre of the mast the best, meaning that when we was our main out and out boom angle increased the distance between the mast and boom vang will remain the same, giving a constant boom vang tension. This whole set-up will be discussed in more detail once it has been built

2010-08-30T22:00:00.003+10:00

Just weighted the hull.

currently at 35 kgs that includes:

Hull
Floor glued and laminated in
1 side tank
Bulkheads
bowsprit structure
transom bar
Gantry
Carbon blocks for fittings (almost 0.5 kg)

The class minimum weight is 51kgs including control lines and bowsprit.

So i figure 5 kg more in glue and fibreglass, 3-4 kg more in fairing compound and primer allowing 7 kg for fittings, bolts, ropes and foot loops.

So at this stage its looking like i should be able to fetch the minimum weight with not too much hassle unless the hull requires a lot more filler than first thought or paint.

Current progress

2010-08-29T22:50:00.003+10:00

This is the side tank under vacuum on the side tank mould. I was quite happy with how this process worked. Using only 5 supporting frames and a 3mm sheet of melamine coated MDF as the mould surface the shape held very well, even under vacuum there was no distortion or warping.
This is a roughly trimmed side tank, this will be going on the port side and will house the spinnaker to keep the cockpit neat and tidy. The mould gave a good smooth surface which should be easy to paint straight to will minimal filling and sanding.

This is the "tension member" that I have Incorporated into the hull fit out. The idea behind it is to help triangulate or form a space frame between the mast step and stay mounts to help increase the stiffness of the hull and rig, which hopefully will help to reduce fore stay sag when sailing, which may ultimately allow for a wider range of rig tensions to be used. The member only weighted 280g so hopefully the advantage will be worth the small weight penalty.

This is a quick image of the fore stay mount attached to the top of the bowsprit receiving tube. The plate is made from two layers of 2mm thick 0/90 deg woven prep reg plate, then extra layers of 0 deg fibres to deal with the tensile load and +- 45 deg fibre to resist "shear out" of the fore stay pin

This is a photo of the rear bulkhead that supports the bowsprit receiver tube. The bulkhead is glass and foam with local carbon reinforcement to help distribute the load to the hull. The joining tape for the bulkhead to hull joint is laid on the -+ 45 deg to provide good shear strength in the joint.
The floor has finally been glued into place using Q-cells and epoxy.

The centreboard case was opened up and the polystyrene foam was dug out.

This is a photo to try and show the collapse that we found in out rudder. That surface was the upward facing surface in our mould when we used to expanding epoxy foam. It looks at this stage like it was a large air pocket or void which has collapsed for some reason after it was made. Although we are uncertain why it collapsed as the carbon skin should want to stay in its moulded shape so they must be some sort of suction or residual stress present to force it to collapse, time will tell...

Also completed but i don't have any photos at this stage, the port side tank has been fitted, starboard side tank has been laminated, rudder gantry fitted and trimmed, spinnaker opening shaped, spinnaker chute has been laminated and carbon plates for fittings have been cut.

Bring you more photos shortly.
Cheers

Quick update

2010-08-19T21:18:00.002+10:00

Above are a few images of the new side tank moulds. They were made using five 16mm MDF templates glued to backing strips then a sheet of 3mm melamine coated MDF was bent over the frames and glued down. Hopefully this set up will be able to resist the loads put on it from the vacuum bag, only one way to find out i guess. Plan is to pop one of these out this weekend.

Above is an image of us doing a rough fit / check of the foredeck and floor panels. Both of the these were pulled straight from the CAD model and fitted really well straight away. The foredeck template was also useful in highlighting how much the hull actually moved / spread out once it was removed from the jig.

This is a photo of the bowsprit receiver tube that i thought would be useful to share. Basically to fit the receiver tube a section was cut out of the bow and a simple bulkhead with a hole cut in it was made to support the back. The section that is on the stem will have a fairly substantial laminate (3-4 layers of 300gsm UNI + 1x 200gsm cloth) wrapping over it and down both sides of the bow. The bulkhead will then have a few strips of uni and some cloth to take to load to the gunwales and down lower on the sides of the hull. This area is going to have a few more little tricky bits and ideas thrown at it over the next couple of weeks so I'll keep you updated.

2010-08-10T22:12:00.002+10:00

Floor ribs laminated in, centreboard case laminated in, bulkheads laminated in.

Next on the list:

Fitting bowsprit snout
Fitting floor
and building side tank moulds

I'll through some photos up shortly

2010-08-07T20:05:00.003+10:00

quick update of todays work:

Bulkheads glued in
Floor ribs glued in
Centreboard case glued in

Plan for tomorrow,
Laminate in place all of the above and trim/fit floor and mast step area.

mucking around with paint schemes

2010-08-03T22:00:00.002+10:00

current thinking is red hull/deck/side tanks with white floor, carbon fibre finish on; transom bar, gantry, rudder box, foot rests. Then black gunwhale and fore deck grip. P.s. i'm also open to suggestions for paint schemes and names.

update:

2010-08-03T21:27:00.005+10:00

Over the past week we have been a little busy. Firstly we finished making the mouldings for the dolly, took the hull off the jig, laminated the inside, began fitting internal ribs.
We made the dolly last year after undertaking a basic TIG welding course at TAFE one night a week for a semester. As our final project we made the dolly for the cherub using 60x40x3 6061-T6 aluminium and used 25x1.5mm 316 stainless steel for the axles. All up in materials i think it cost about $200 plus $40 for wheels from eBay. So to fit it to the new boat all we needed to do was make a support for the hull. Note: The reason we used such heavy section aluminium was because of the way our boat sits on our 8x4 ft box trailer.

The above image is the centreboard case as it came out of the vacuum bag as you can see it pulled into the corners quite nicely and the overall finish is pretty good. The second image is the Styrofoam beginning to be melted out with acetone, after beginning this i realised it would have been a much better idea to leave to foam in there until it was in the hull as it is quite flimsy, so i stopped. Although i did notice that acetone was able to seep from the inside to the outside of the skin even though there was 4 layers of 200gsm glass, so it looks like i will need to paint the outside with a coat of resin to help make it water tight after it is in the boat.

I thought this image was worth adding this is the size of the extra reinforcing patch i used under the mast this was 1 200gsm carbon cloth on the 0/90 degree angle to the centre line (compared the the main hull skin at -+45)

I thought this was a good image to add showing the laminate wrapping around the hull/chine. Overall i was pretty happy with how the -+45 laminate laid over the hull and continued to stay approximately at -+45 as we worked towards the bow. I guess I'll see how good that decision was when we come to trying to fair the hull.

The first image is the jig again once once the hull was removed, the second showing how it was able to flat pack and store easily (to dismantle the jig only took 15mins and a electric screw driver)

This image is of the legs of the table/jig, i thought it was worth mentioning how we levelled the jig. Because our jig design had a table with 5 legs it was important to have the leg length adjustable to account for the un-even floor of the garage and our assembly etc. So we used a "coach- screw" in the bottom of each leg allowing the height to be adjusted simply with an open ended spanner.

This is the hull as it can off the jig.

This is the hull after we laminated the inside of the hull, same lay-up as the outside as it is very important to try and keep the laminated balanced so that when the hull is loaded up it doesn't try to warp. Also the floor ribs have been trimmed and ready to glue in and the centreboard case has been roughly fitted.

These are foils after we sanded the recess on the leading edges ready for their joining tape (1x 200gsm layer at -+ 45 to the centre line so it drapes well over the corner the fibres are at the right angle to resist the shear loads at the join)

Its go time....

2010-07-30T22:57:00.002+10:00

Outside of hull was laminated last week, dolly and supporting cradle has been built and finished yesterday. The hull is ready to remove from the jig and flip over this Saturday. Then we will be able to laminate the inside on Sunday.

From there on in it is all hands on deck almost 6 weeks to the sailing season (looks like it might be a few weeks late). The two images above are some of the printed out templates of all the cockpit and interior. This is what I'm hoping will help drastically reduce our build time and where having a 3D CAD model of the boat should come into its own.

After the hull is laminated on the inside the internal structure will go into the boat in stages in the night time after uni during the next two weeks. Once the components are positioned and glued in place we will come back later and laminate / vacuum bag them in. I'll update with more photos after we flip the hull.

idea for laminating the centrecase

2010-07-20T22:26:00.004+10:00

This is my idea for laminating the centrecase into the boat hull.

Firstly when we build the cradle, we make sure the area under the centrecase is well supported. Then mark out the area and grind away the foam so that we are left with the outside skin only in the centrecase area. Then the centrecase is trim, aligned and positioned. This is then bogged into place using a strong filler such as a glue powder or some sort of fibre filler and a small radius is made between the outside edge of the case and the hull skin.

Once this has cured and been neatened, the first laminate is done and cured. After this a foam wedge or filler piece is bogged into place using a light filler such as Q-cells and the second laminate is done over the top to tie everything in.

The reason for this double laminate process is because it allows you to distribute the load from the centreboard case into both the top and bottom skins and providing a large area to spread this load on the case its self.

Also note that in a loaded case such as a centreboard the hull exit is under twice the load of the centreboard head/floor exit so the hull exit needs to be particularly strong and the floor exit can be made a little lighter.

On the floor exit, I intend to glue a foam strip around the case to the height of the underside of the falsefloor so that it can just drop straight on top / around the case and be glued in place, then reinforce the opening from the topside of the floor.

2010-07-18T22:14:00.002+10:00

Above image is an assembly of the cad models i have been using to size and design components. The layout is not 100% of what i intend to use, but it has been extremely helpful in locating important points and dimensions. It has also allowed me to investigate the size and shape of the side tanks so that i can ensure it meets the class rules as well as provides enough space in the side tank to fit the spinnaker chute.

This is the centreboard case i intend to use, it allows the centreboard to have 200mm of movement fore and aft so that I can tune the centreboard position to the new rig and rig position. The adjustability comes from using different cover plates, both of the these plates on top and bottom are held together with a threaded rod. The cover plates are made custom for each centreboard position that is needed.

Above is an image of the cover plate in place, this top surface will be flush with the top skin on the false floor.

This is the centreboard case in the vacuum bag. It was constructed by shaping a piece of extruded polystyrene foam called "ISOBOARD", which is normally used for insulation. This was then laminated over with 4 layers of 200gsm glass cloth on the -+ 45 deg so that the cloth would pull into the tight corners. It was decided that 4 layers should ensure that the case is water tight.

Hull laminated.... almost

2010-07-17T18:36:00.002+10:00

Finally started laminating the outside of the hull today and halfway through ran out of carbon... looks like we used a lot more that we thought making the previous components for the boat. On the plus side, having the cloth on the -+ 45 degree allowed the cloth to draped over the chines quite easily. Also using scrapers/spatulas to wet out worked extremely well even on the curved surface of the hull. The peel ply was used to help soak up any excess resin and help prepare the laminate for secondary bonding of paint and fairing compound.

Looks like the next opportunity to pick up some cloth and finish the hull will be Thursday so hopefully not to much time will be lost. I will be able to pull the profiles for the cradle of the CAD model tomorrow so we can build the cradle while the hull cures. We will also be able to construct the centreboard case, member for the space frame, spinnaker chute and side tank mould in parallel to laminating the rest of the hull.

hull shell ready for laminating

2010-07-14T17:10:00.003+10:00

Finally have finished putting foam onto the jig. We have faired in any rough areas and are ready to laminate the outside of the hull. The outside laminate will be 1x layer of 200gsm plain weave carbon cloth laid in a +- 45 degree axis with respect to the boats centre line. The main reason is to help increase the torsional stiffness of the hull and secondly the cloth will drape easier over the chines and sharp corners of the hull. A reinforcing layer will be placed over this to help spread take the load from the mast step and centre case area. This will be approximately diamond shaped and the fibre orientation will be 0/90 degrees to the hulls centre line. This laminate will be mirrored in the inside of the hull.

here are some photos of the hull ready for laminating:

Transom of the hull, about 10mm of curvature so almost flat.
Bow area certainly seems sharp and fine, although the intersection between the chine and bow is lower than the Matthew's hull. This means that the bow might not actually be as fine as i was hoping, I'll need to see two hulls together to find out how much finer we have made it.

A view from the back of the boat, its difficult to get a decent shot in the garage of the true shape of the boat so I'm looking forward to when we can take it off the jig and move it around a bit.

The current plan is to laminate the outside of the hull on the weekend then begin constructing the cradle next week.

We will be just using a simple wet-layup technique on the outside of the hull using plastic spatulas/scrapers as much as possible then applying a fine peel ply to help absorb excess resin and give a surface that's almost ready for secondary bonding.

2010-07-02T21:46:00.003+10:00

Tiller looks fairly good, perhaps a little heavy at 370grams without clear coat paint, but it is very stiff due to the large cross section used at the box. So i should be pretty safe from breaking it if i try to support a bit of my weight on it.

Hopefully will be glueing the finaly pieces of foam on the hull tomorrow so we can get it ready to laminate during the week.

a few bits

2010-06-30T23:23:00.003+10:00

Work has been slow over the past week or two with thesis work at uni ramping up a bit. Last night we laminated the new tiller for the rudder box, which is a fairly simple straight tapered tiller. I'll take it out of the vac bag tomorrow and let you know what the weight is.

We visited CST today and picked up a carbon recieving tube for the bowsprite 50mm ID x 400mm 2mm wall thickness long carbon tube (about 200g) and collected a qoute for a new mast. We are still unsure at this stage what we are doing about a rig, but considering we are planning to sell heart shaped box (3064) it looks like we will be buying a new one.

Our plan is to finsh the foam sheets on the hull this weekend and to laminte the outside of the hull by next weekend.

2010-06-14T19:37:00.004+10:00

Its been a fairly busy weekend in the garage, with a significant amount of work completed. As can be seen above, we placed the sides onto the jig and they conformed pretty well. The sides were done in two pieces and joined slightly forward of the midpoint in a position that didn't experience much bending.

We also managed join the panels in the bottom of the hull and and glue them at the chine. Now only the forward sections of the hull need to be attached. Then we can begin trimming up the chines and getting it ready to laminate the outside of the hull.

We also managed to make a few components to help take to load off further down the track. The image above is a bracket for holding the self tacker track ends to the flat foredeck. This is the same arrangement as used on my old boat, but just made a little neater this time around. (The item above is cut into two brackets and trimmed up to be fitted to the boat)

This is the rudder gantry being laminated on the mould. The layers on the underside were laminated straight to the mould and then the foam plug was placed over the top and laminated over. The lay-up consisted of (1x carbon cloth, 2x 300gsm UNI carbon) each side and a 30 x 25mm foam core. The flat panel on the bottom is to prevent the gantry from "catching water" as this was a problem with my previous design (mainly because it was mounted to close to the water).

The above image is with the final later of carbon cloth ready for the peel ply, release film, breather and vacuum bag.

This is the gantry in the vacuum bag.

Above is the mandrel for our new boom. Simply a 20 x 20 mm steel box section with 75 x 50 mm strips of polystyrene foam glued each side. The steel is the keep the foam straight when shaping and laminating. My aim is to shape a boom with an elliptical cross section that tapers from goose-neck to boom tip. It will be maximum depth at the goose neck (class rule: must pass through a 104 mm ring) then taper to approx 60 mm at the tip end.

After this weekend the remaining components to manufacture are as follows:

Laminate tiller / build rudder stock
Laminate transom bar
Build side tank moulds / make side tanks
Design / build centre case
Foreword tension strut for rig space frame
Foot rests for floor

Then basically finishing the hull shell and putting it all together, easy right?

Jig is finished

2010-05-30T18:47:00.011+10:00

We managed to finish lining up the jig on Saturday and covered all the edges in packaging tape and plastic so that the foam will not stick to the jig. We put a tape measure of the jig and discovered that it had grown 20mm in length somewhere along the line. I spent several hours thinking about this today and for the life of me still can't find out where we went wrong. I was pouring over this drawings, 3D cad model and measuring everything on the jig, everything was as it was supposed to be except the final length. So once i work it out I'll let you know what it was. This does effect the boat (especially the bow) but it looks like we will be able to fudge / fair it in and we should be alright.

We began placing a full sheet (2200 x 1200 x 10 mm) of foam over the back half of the hull and tested out our methods of attaching the foam to the jig. We tried stitching the foam to the jig with a non-waxed sail makers thread and a small plastic spacer on top (so it would pull through the foam). We would then tighten this row of stitching in one go and pull the foam down to the jig surface.

At this stage its looking like the jig design of only using lateral supports, although simple to setup and line up it may not provide enough support to the foam sheets. As you can see from the last photo we are getting an uneven shape / surface at the chines. I feel this is because of several reasons, the first being that we are pulling to tight on the sewing thread and flattening the sheet against the top of the jig frame, rather than pulling it down to the one edge, which it is intended to sit on. To get around this we are going to try and develop a better way of attaching the foam sheet to the jig frames, which we and adjust each "stitch" on its own.

Secondly, because of the large sheet size it may require it to deform two much when it pulls down to the frame and forcing the foam to buckle or warp between the frame members. We can get around this by trimming the sheet into smaller pieces and joining them as we go, so that the joins form a "seam" such as in a sail.

The above image is of our rudder gantry that has been shaped and ready to be laminated

Intial jig setup

2010-05-24T21:13:00.006+10:00

The photos below show the intial setting up of the jig, this was suprisingly quick and everything seemed to fit fairly well. The final accurate lining up of the jig will take place shortly. So from some of these photos you can begin to see the shape of the hull.

Also we had a quick look at bending the foam over the jig. It looks fairly good in places but we might have a bit of fun / difficulty in some areas. Also it will be interesting to see how the spacings go, as the foam was quite flexible / unsupported so only time will tell. If the foam is not supported enough, one option may be to laminate the inside of the foam strips with a light glass cloth to stiffern them up.

Fore-deck lay-up

2010-05-24T19:56:00.009+10:00

This weekend was fairly successful in regards to boat building, with the last of the flat panels laminated and the hull jig initially setup.

Above is a table prepared to laminate a glass/carbon fibre plate so that it can be used to attach fittings to the hull. The plate is intended to be 5 mm thick and about 330 x 250 mm, this was approximately 24 layers of 200 gsm E-glass and 4 layers of 300 gsm UNI carbon.

The plate will be cut in to small strips that will be inlaid into the cockpit floor and side tanks so that threads can be tapped into them and fittings can be attached without the use of nuts and washers. I also intend to perform some testing on this method down the track to see how strong the threads are in the glass plate.
Above is an image of the glass plate under vacuum. Notice the black irrigation plastic and fittings used for vacuum bagging. By using these pipes I can make a manifold and have multiple vacuum lines coming off the same pump so that as the day progresses and I laminate more things i still have access to the vacuum without interrupting the previous layup. Also it allows a cheap way to put a valve/tap into the system, which means you can initially control the speed at which the vacuum is applied to the bag (which can be handy for tricky items, or tight bags).

Above is a lay-out I used on a sheet of foam to fit the bulkhead, floor support ribs and bowsprit 'V-beam' to try and get the best usage of foam. Some the panels are laminated, I will get the individual components printed full size on paper so that i can check the fit. Then I will be able to use the paper print out as a template to cut the panels. I'm hoping that this will allow me to speed up the bulkhead/floor rib fitting process considerably, which can take quite a bit of time to fit to the curvature of the hull correctly.

This is how we laminated all of our flat sheets. Firstly the panels were marked onto the foam sheet with pencil so we had an idea of where reinforcements and laminates would go. Secondly a slightly runny bog of epoxy and Q-cells (micro balloons) was made and spread over the entire sheet with a 150 mm wide plastic scrapper (this are very helpful for laminating flat panels and only cost about $1). This is to fill all the open cells in the foam with a lighter bog rather than with straight epoxy resin.

Next the uni-direction carbon reinforcements were laminated on the bulkheads and other areas. Then the 200 gsm E-glass was placed over the entire sheet, the epoxy resin spread out again using the 150mm plastic scrappers.

Peel ply is then spread over the entire laminate, then perforated release film to control the amount of resin removed during vacuum bagging. Finally the breather fabric was applied and the whole panel was flipped over and laminated on the other side.

Note: To make vacuum bagging easier, use a can of spray glue such as 3M super 77, to apply the release film to the peel ply and the breather to the release film. Otherwise it may move around and be difficult to put into the bag.

This is the flat sheet under vacuum in the bag, unfortunately we ran out of breather fabric so could only place it on one side.

This is the resulting panel after the release film and breather fabric was removed.

This is our rudder gantry, we started but laminating foam strips on the mould so that we could then shape it afterwards. This will allow is to laminate the gantry mould, place in the shaped foam core and laminate the other side in one go.

false floor bagged

2010-05-17T23:53:00.005+10:00

The above image is of the false floor (approx 1900 x 1320mm) being vacuum bagged while it cures. The lay-up for the floor was 10mm 80kg/m^3 foam with a layer of 200gm^2 E-glass layed on the +- 45 deg to the centreline and an extra layer of 130gm^2 E-glass at 0/90 on the topside. This lay-up was chosen for several reasons:

1. The cloth was layed on the +- 45 so that i can create a "torsion box" with the floor, hull sides and hull underside between the mast and the transom (all of which will have laminates on the +- 45). This it to help create a stiffer hull with reference to torsion induced between the skipper downwind (back corner of the boat) and the rig trying to rotate in the opposite direction.

2. The 130gsm layer was added to the topsurface because on my old boat 1 layer of 200gsm was not quite enough and pierced easily, while 2 layers of 200gsm was better it seemed slightly heavy.

Also note the floor has two lateral stiffeners, which are an additional thickness of 10mm foam and capped each side with 300gsm Uni carbon. This is to help increase the stiffness of the floor as there will only be two stringers running parrallel to the centreline that support the floor.

This is our new rudder gantry mould. This was made from 18mm MDF then brushed with epoxy. The design is based on the one off my old boat, but approx 50mm higher at the bottom gudgeon than the last design to help keep it clear of the water at low planing speeds.

This shows the foam strips being built up and glued into place. This will result in a member that is 30 x 20mm once it has been shaped and faired. Also notice this mould incorporates a flat section from the lower gudgeon to the hull, this is so a thin laminate (2x 200gsm carbon) can be layed there to help further prevent the gantry from dragging in the water.

Whats next?

by approx 29th of May i hope to have all flat panels laminated (fore-deck, floor ribs, bulkheads, bowsprite support, spinnaker tunnel and tension members to take rig loads). As well as the transom bar and rudder gantry laminated. Then we can clear off the work table and assemble the jig to start on the shell.

Centreboard delamination

2010-05-09T21:11:00.004+10:00

On Thursday morning last week we began releasing the centreboard from the mould. When we separated the two moulds halves we were very disappointed to see that one skin of the centreboard had torn its self from the foam core. Later it was found to be the electrical tape we had used to create a recess in the leading edge of the centreboard that had stuck heavily to the mould. This created a tensile force between the skin and core at the leading edge of board.

As can be seen from the image above the foam core failed in tension then the fracture propagated to the skin where the foam (not the foam / skin glue line) continued to fail in tension due to the peeling force. We then had to fill the void with straight epoxy resin and re-close the mould to rejoin the skin to the foam core.

This is what we learnt from it:

1. We should have put PVA or wax on the electrical tape and not just relied on the smooth plastic surface for a clean release.

2. That the foaming resin is a lot weaker than we first thought after two days of cure time. The data sheet recommends that the foam be post cured at 50 degrees for 16hrs to obtain the best properties.

Note: The board in the unpainted state weighs 3kg

Centreboard

2010-05-04T20:58:00.004+10:00

This morning we joined the centreboard together with the expanding epoxy foam. We poured in 1.8kg of expanding foam it looks like about 100g of foam has expelled out of our outlet hole in the mould. The below images are of the centreboard mould clamped together and also of a footstop mould made today.

The footstop will basically be a carbon fibre (clear finished) foot rest for the crew to use when getting out onto the trapeze. There will be one each side of the centreboard case approx 600mm long and positioned parallel to the centre line of the boat. The mould was made by folding 3mm sheet aluminium into the given shape.

Questions

2010-05-03T23:13:00.001+10:00

Also if anyone has any questions at anytime please feel free to ask by commenting below the post and i'll do my best to answer them as soon as i can.

Cheers Adam

Releasing rudder

2010-05-03T22:55:00.006+10:00

The rudder released from the mould relatively easily, except the electrical tape we used on the leading edge to create a hollow for a carbon tape later on turned out to hold the blade in the mould and took a little bit of work to release. The blade at this stage has an extremely fine trailing edge, which we will trim back a little to help prevent damage. Although when releasing the blade it did look like there my possibly be an air pocket or a section on the leading edge that hasn't bonded properly. So i will need to do some investigating into that later in the week. Also rudder blade out of the mould was 1.5 kg I think the amount of carbon that went in was 500g on the rudder (total) and 900-1000g in the centreboard (total)? i probably should have written that down, mybad.

Although there is also clear 2-pack paint to go over the carbon finish to;

1. Help fill any hollows and give a little bit of material to fair the board with.
2. To make the carbon look good.

Tip: When trying to release something such as a rudder blade from a mould, try to work from the head of the board as this is the stiffest end (as opposed to the tapered tip). So that instead of flexing the board in mould, you are actually lifting it from the surface effectively.

Centreboard lay-up

2010-04-30T00:37:00.009+10:00

This is a photo of the rudder layup after the peel ply had been removed and the surface was given a light sand ready for the foaming epoxy. Notice the shape of the uni layers, i did this to try and remove excess material were it isn't needed for example the front and rear sections of the foil. As the middle section (thickest) takes the majority of the bending load, and the narrow areas contribute very little to strength and stiffness.

This is the hole drilled into the top of the rudder mould so that excess foam could be allowed to escape from the mould. There is a straw in the hole to prevent the foam sticking inside the hole.

This is the amount of resin we used this time, as you can see from the image it looks like possibly a little to much (this stuff expands to 4 times its volume). We brushed all surfaces as suggested by SP Systems.

This is the excess foam pouring out of the mould, turns out after our failed test pour we got a little carried away. At least there shouldn't be any gaps in this one.

This is the centreboard layup that i used, similar to the rudder in profile and shape, except 1 extra layer for good measure. The layup is as follows:

1x cloth 200gsm cloth at 45 deg
1x full uni 300gsm
6x tapered and progressively smaller layers of uni 300gsm
1x small patch of 200gsm cloth at hull exit.

We applied to the mould i felt that this was way too much carbon, time will tell i guess you never know the extra stiffness might be worth it.

Applying the clear epoxy as a gel coat to the mould beforehand. This was done with a spray gun on the rudder moulds but we could not get it to spray the epoxy well and this gave us a very poor surface. The image above shows us using the gun as cup to hold the resin to brush on after we gave up on the spray gun.

The above images shows the centreboard under vacuum, with the bleed out clearly visible.

Plans for the weekend are the join the centreboard and remove them from the moulds.

Rudder Lay-up

2010-04-30T00:19:00.007+10:00

The above photo is showing how i cut the carbon cloth for the laminate. Instead of cutting the cloth dry to a rough fit or a close fit that frays every where and becomes messy. I laminated a large piece of cloth (measured beforehand) onto a plastic sheet (vacuum film in this case) once the cloth is wet out a second layer of plastic is smoothed out over the top. This gives a "Poor mans Pre-preg" where you can handle the cloth without it distorting or covering everything in resin. Then using a template and marker pen, the shape is traced and cut with scissors to give a neat non-fraying edge.

The backing plastic is then peeled off one side and placed into the mould carefully. With the backing plastic still on the carbon is stable and you can pull it up as many times as needed for a good fit.
Once it is placed in the plastic is peeled off and the rest of the laminate is applied like normal. I cut the carbon cloth on the +- 45 deg so give the board a greater stiffness from twisting. I also read recently that placing fibres on the 45 deg over Uni's helps to support them in compression so that they resist buckling better. This should help to give a stronger skin in compression. the rest of my rudder lay-up consisted of:

1x full cloth 200 gsm
1x full 300 gsm uni
4x tapered and progressively smaller layers of 300gsm uni.
1x cloth 200gsm on 45 patch at box exit.

The tapered layers resulted in the majority of the material on the max cord of the foil and around the box exit, (some tapered above this to the head of the board as well).

Both mould halves under vacuum. The bagging process was fairly standard, peel ply, perforated release film, bleeder, breather (shade cloth) then the bag. If you look closely at the above image you can see the bleed-out through the perforated release film.

Expanding foam test pour

2010-04-30T00:06:00.005+10:00

Clean garage, ready for work.

This photo is of the first test pour of the expanding foam into the mould to make sure that the process would work without producing large air pockets.

Using a rough solidworks mould it calculated the volume of the rudder to be 2.35 L. The amount poured into the mould was calculated as enough to fill this space.

As can be seen from the photo below, this pour did not turn out so well. Firstly the largest problem was that obviously there was not enough foaming resin in the mould. After checking the volume of the mould with water it turned out to be about 4L not the 2.3L that was calculated. This resulted in a large number of voids and unfilled cavities as well as not filling the mould the whole way.

After talking with SP it was suggested that the resin should be brushed on all mould surfaces before joining the halves together, as well as use the correct volume of resin.

2010-04-22T22:40:00.002+10:00

Expanding foam for the foils arrived today, hopefully going to run a few sample / test pieces on saturday aswell as a test blank to make sure the mould will fill without any air bubbles or atleast if air bubbles form we can see what to expect. I'll update with photos after the weekend.
If anyone is interested here is the data sheet for the AMPREG F230 expanding epoxy foam:
http://www.gurit.com/core/core_picker/download.asp?documenttable=libraryfiles&id=1546

The JIG has arrived

2010-04-20T21:29:00.004+10:00

The jig was completed at the CNC cutter this morning and I was able to pick it up shortly after. The initial rough quote was $500 for materials and cutting time. After i simplified the jig design to reduce the cutting time a little. The final cost this morning was $374, this covered approx 1 hr of cutting time (@ $220 an hour) and 4 sheets of 18mm MDF. The images below are just a quick mock assembly of some of the jig to check if everything was okay, which it appears to be. I haven't double check any measurements yet but i will do in the near future.

I'm still waiting on the expanding epoxy foam, which should be here before the weekend so that i can make the foils and return the moulds so there is room for the jig to be assembled. Also now that i have the jig we need to drill holes around the edges so that we can attach the foam sheets. We are also going to paint the jig with old paint to help protect it from moisture and hopefully allow another hull or two to be built off it provided the design is okay.

Preliminary FEA on centreboard

2010-04-15T11:06:00.004+10:00

Here is a very preliminary finite element anaylsis for the centreboard for the new cherub hull.

Basically this was performed in COSMOS works, which is the solver for Solidwork 2008. The board is treated as a solid board made a aluminium. The head of the board is fixed, e.g. restrained in all directions. Then the top surface is loaded with a pressure acting to bend the board downwards. The purpose of this analysis was to try and determine what is the best shape of the individual layers of carbon cloth so that i'm getting the best use out of it as possible for the weight.

This image is a plot of the Von Misses stress, which is a method of determining the overall stress in an object. the red areas are under high stress, while the blue is under lower stress. From this i can select a certain stress level and see what its shape is over the surface.

The image above shows the outline of a certain stress level. This suggests that if i make the individual layers close to this shape i should be getting the most out of the material for its weight.

Hopefully this arvo i will be able to use the newer version of this programme at uni to actually make i model that has carbon skins and be able to not only determine the shape, but also how many layers are needed and how much the board might flex under load.

2010-04-14T17:02:00.002+10:00

Whats happened so far:

1. I'm currently still waiting on the AMPREG F230 foaming epoxy resin that i order from SP systems so that i can do some tests with it. Then hopefully use it to make a centreboard and rudder. I was told it was going to be in the warehouse on the 6th of April, but they are still mucking around and haven't got it sorted. So best case at this stage is that it arrives on monday.

2. The jig is scheduled to be finished at the CNC cutters by Monday 19th of April. So at this stage i won't be able to put the jig together until i'm done with the centreboard and rudder moulds as they are using up all the table space. So best case at this stage is that the jig is assembled and ready to go in two weeks time.

3. I did some quick calcs today with regard to volume of foam and area of glass to be used in the hull shell. As a blank shell that is glassed without a centrecase or reinforcements etc i'm looking at the following:

Target weight: 11.7 kg
Epoxy used: 3.0 kg
Cloth used: 15.2 m^2

Also had a quick look at the fore deck:

Target weight: 2.4 kg
Epoxy used: 0.5 kg
Cloth used: 2.6 m^2

These calculations were done by taking the surface area of each section (extracting from solidworks) then based on a 50% Fibre Volume Fraction, which is reasonably achievable by careful hand-layup i'm told.

These calculations are all part of trying to put together an accurate list of materials needed so that we don't purchase too much at the beginning.

What i've got planned in the near future:

1. The 2009 version of Solidoworks (a 3d modeller) is now available on the computers at uni, which has the ability to analyise simple composite structures. With the use of this i intend to model a centreboard or rudder and perform a simple Finite Element Anaylsis (FEA) on it to see how i should stagger the lay-up within the board, so that i can remove exess material in areas that are under-stressed. I will post the images and results from this on the blog once it is completed.

2. Complete a materials list and have materials for the boat hull delivered before May hopefully.

Also if anyone has weighed their bare cherub shell from the mathews brothers when it was delivered i would be interested to find out how much it weighed. Thanks

2010-04-06T16:46:00.004+10:00

These are a few photos of the garage in a moderately clean state for us before we begin cleaning / construction, just as a simple before and after reference.

Also went to FGI this arvo to obtain a rough quote for materials. With a rough estimate using the "NSW Cherub Schedule" spreadsheet provided by Rolf as a guide to the amount of foam needed, the following was estimated.

8 x sheets of 10mm, 80 kg/m^3 Klegecell foam = $1150
46m 200 gm^2 E-glass = $315
4m 200 gm^2 Carbon = $180
10 kg Epoxy resin = $220
Plus consumables

Rough quote is $2000 for hull materials, using mainly E-glass.

CNC machining of jig (including MDF) is rough quoted at $500

2-pack paint for hull and tools for construction approx $500

At this stage a rough cost for the complete hull is $3000 upon which a rig, sails and fittings are needed.

Design of the jig

2010-04-05T18:51:00.006+10:00

(top) - All componets for jig
(middle) - Aft view of jig
(bottom) - Front view of jig

The jig is designed on having a vertical frame at a one-foot spacing from the bow to the midpoint with one and a half foot spacing from the midpoint to the stern to reduce the amount of materials used in the jig.

My intentions with this jig design were to employ the use of CNC routing to create very accurate profiles and positioning mechanisms so that it would drastically reduce the amount of time spent on constructing and aligning the jig. The panels will slot into place on vertical boards that are attached to a table. The table will be constructed out of 140 x 45 mm pine for the edges to create a very stiff and sturdy table (as each full sheet of 18mm MDF weighs approx 30kgs). This is important because of how the jig is setup, without the use of battens to fair in the sections it must be very stiff to provide the accurate hull shape.

Another design consideration with the jig was transport and storage. With this design the flat jig MDF panels can be laid flat in a small box trailer and the table tied on top or stored flat somewhere saving space, also the table will act as a work bench once the hull is flipped over and a sheet of form ply is placed on the table top.

The design was given to the CNC cutting workshop just before Easter and are expected to be completed in mid to late April. At this point hopefully centreboard and rudder will be completed and the focus can be placed on the jig and hull shell.

2010-03-31T22:06:00.004+11:00

This is the final design i have settled upon after four iterations. The rocker was reduced by 20mm so that the height of the chines intersecting the bow could be raised by a further 40mm to allow a finer bow to be acheived. Also the curvature positions were reduced to the minimium third in the midsections of the boat, while increasing to the maximium postion near at the transom.

2010-03-31T21:41:00.002+11:00

This was my first attempt at desgining a new cherub hull for the 2010/11 season. Transom and midpoint on minimium with a very flat transom.

The programme I used was a 3D solidmodeller called Solidworks, i orginally tried using a CAD programme called Multisurf which was more aimed at boat hulls but was difficult to use and the infomation extracted from it wasn't as useful as Solidworks.

My intentions behind the design was to build a hull that would be very fast in moderate to heavy air conditions. As i believed it would give me the best chance of doing well in the up and coming national titles in Adelaide. For this i agreed on a very flat transom for effecient hard planning downwind and a very sharp bow to deal with chop from stronger breezes. Although this finer bow would create a boat that would nose dive easier it was countered by the reduction of the transom width. This had two purposes 1, was to allow the transom to "sink" by shifting crew weight further aft to raise the bow in the event of a close nosedive and the second was to reduce the plannnig area for faster planning when flat out downwind.