25 foot trailer yacht - Rudder Questions
I have a GRP 25 foot trailer yacht that I'm wanting to improve the rudder on. Basically the foam GRP one I have weighs almost 10kg and is not optimised in shape and its leading edge is 40mm aft of the gudgeon pivot line - It feels like I'm dragging 2 buffalos!!
I intend to construct a new one out of Divinycell (HD) / e-glass / epoxy resin (resin infusion) - and wanted a few tips if possible on the following subjects?:
1) Is the green code Divinycell suitable? blade is approx 1300mm x 360mm - and will need two 20mm thick sheets laminated together with e-glass in between for datum line and strength at the edges
2) What would you recommend in terms of laminate cloths? Someone suggested two layers of uni-glass or carbon followed by a single tri-axial sheet??
3) What additional thickness allowance do I need to make for the 3? skins (what cloth weight should I use)
4) I'm getting assistance from a boat builder but just wanted a 2nd opinion on things - The trailing edge is the difficult one as we need to have a thickness of no more than 1-2mm here. We are using a modified NACA 0012 section with hollowed out trailing edges (concave on exit straights)
5) any other pointers you think might be helpful please??:) :)
Any assistance appreciated thanks
What weight is the green code Divinylcell foam. I'd point out that you may want to weight the rudder so that it is neutrally buoyant or a bit heavier than water...so that it doesn't tend to float up.
I wouldn't use uni-glass in this application, since the loads are going to be multidirectional. Triaxial roving would be a good material to use...with some regular cloth or CSM over it to protect it from the fairing/sanding process.
I'd also recommend putting in a layer or two of kevlar, preferably under CSM/cloth but over the triaxial roving. The reason I'd add the kevlar is that it is highly abrasion and puncture resistant.
I wouldn't use Carbon fiber in a rudder, since the carbon fiber can cause galvanic issues with metal hardware, which the fiberglass and kevlar will not.
Hope that helps.
thanks for your prompt reply. As we are racers we wanted the extra buoyancy in the stern - The rudder is a swinging one located in a box - I calculate when fully immersed in seawater the buoyancy will be around 7.5kg - we reckon we can hold it down with the tie-down rope (multi-purchase if need be). Thanks for the good advice:o
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