cep32 5 Posted November 24 Share Posted November 24 It must be sailing season. My Javelin needs a new centreboard so I'm sorting out the shape at the moment. The plan is to have a pine core with a 100mm wide carbon uni strip down the length both sides and sheathed in fibreglass. My concern is how the carbon fibre will load up when my fat 120kg stands on the end of it after a swim. If all the carbon is on a parallel sided part of the board, all the carbon will load at the same time but there are performance compromises. If I use a normal NACA shape without a parallel section, the smaller area of carbon at the widest point will load earlier and the safety factor drops significantly. I've added a couple of images illustrating the problem. Instead of the full width of carbon (the darker bit of line) loading like in the lower image, the much narrower bit in the red box loads first. Is this an issue or will the whole lot flex and load together anyway? Sorry for all the questions but it's never been something I've needed to think about with all the rudders I've made. Quote Link to post Share on other sites
LE Bb 38 Posted November 25 Share Posted November 25 The carbon won't be the problem, it will be pine flexing/crushing under it. then causing the carbon to compress. Idealy you would have a denser timber strip where the carbon is going, like yellow cedar, mahogany, Kauri .... You will get away with pine or western red cedar for the nose and trailing edge A lot of dinghys have one or two layers of carbon uni ( 300g ) you may want to go 3 or 4 Then a minimum of 295/300g glass over the whloe thing ( 2 layers of 200g boatcloth may be an easy option ) 1 2 Quote Link to post Share on other sites
MartinRF 77 Posted November 25 Share Posted November 25 Since the Young's modulus of the uni carbon laminate is way higher than for any of the other materials you must assume the carbon takes the load alone. The curvature of the carbon in your figure is not a problem. https://www.reflectometrist.eu/pages/daggers/index.html /Martin 1 Quote Link to post Share on other sites
cep32 5 Posted November 25 Author Share Posted November 25 Thanks for the advice. I've done the calcs on the basis of the carbon carrying the full bending load so I can get that to work. Given the timber will just be the core, would finger jointed timber be okay as long as the joints were offset? Quote Link to post Share on other sites
MartinRF 77 Posted November 25 Share Posted November 25 44 minutes ago, cep32 said: Thanks for the advice. I've done the calcs on the basis of the carbon carrying the full bending load so I can get that to work. Given the timber will just be the core, would finger jointed timber be okay as long as the joints were offset? I would assume so but I really don't know. I haven't considered that alternative myself. All my dagger boards and rudders, except the latest pair which are 100% carbon, have low density wood cores and so far none have failed me. By low density I mean just north of 300 kg / m³. Western red cedar, redwood, obeche... I think Ian Farrier saw this as the heavy but durable option. /Martin Quote Link to post Share on other sites
LE Bb 38 Posted November 26 Share Posted November 26 nz figerjointed pine shouldn't be allowed anywhere near a marine inviroment. 1 1 Quote Link to post Share on other sites
waikiore 509 Posted November 26 Share Posted November 26 Le Bb is dead right Yellow Cedar and carbon go very well together , I have tested them and many other composites to destruction for some local designers years ago , and every one of us walked away amazed at how it stood up compared with very exotic laminates and foam cores Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.