Thursday, April 15, 2010

Preliminary FEA on centreboard

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.


  1. For your foils are you going to make a female molds? For your FEA analysis make sure the loading is as realistic as possible if you are going to use it to design the laminate.

    Hull weight: For a Javelin the bare hull surface area is around 9m^2 and the average weight is around 23kg and the material are the same as what you are using. Scaling to your surface area of 5m^2 the weight is around 12.8kg.

  2. Thanks Dave,

    The hul weight sounds good, another cherub owner suggested their shell weighed around 15kg when they pulled it off the jig. So its good to have a few figures to aim for.

    With the foils i have managed to borrow some female molds off a good friend to use for the build. The FEA at this stage was just pretty basic, i'm having a little trouble with the more complicated FEA at the moment but should have that sorted shortly. Also once i have it working i do intend to try to load the foil a little better as well.

    Thanks Adam

  3. For the FEA start with a simple structure such as rectangular beam for which you can verify the result produced by hand, before going onto a more complicated shape such as a foil in any detail. That way you can build some confidence in the results you are achieving.

  4. Adam,

    Have you also tested putting a weight at the end of the board to simulate you getting the boat up again? :-)