As most/all of you know I am working on a 52" scale Transpac 52. I was thinking, although there are many RC classes and boat bigger than this, this might be approaching the lower end of the size spectrum to allow the use of a honeycomb sandwich for the hull. My thought was a layer of 5.7 oz carbon, a layer of Nomex honeycomb (.21 in thick) and another layer of 5.7 oz carbon. I know this would be overkill but it would create a hull stiff enough that barely any bracing would be required other than around the keel box/mast step. This is a cost doesn’t matter scenario since I could probably build a pure carbon hull for the same price as the honeycomb hull. Just thought I would see what everyone’s opinions are.
What scale are you working to Millrtme?
61.5 inch is 1:10 for the TP52.
1:12, or 1"=1’, same thing right? It still results in a large boat, but def. easier to transport to and from the water.
After doing some more research this idea would be UBER EXTREME overkill. A .21 core would offer 1500 times the stiffness of the 2 layers of 5.7 oz carbon alone. A buddy of mine built an A-class cat with a .25" core. He recommends, sticking to just carbon, but if a core is really needed/wanted just use 1/16" balsa core (end grain). Sounds like it might not be a bad idea to lay up two layers of carbon, cure them, then place balsa where it’s needed and then add one more layer of carbon. But maybe a full core balsa hull wouldn’t be a bad idea anyway. More research will undoubtedly yield a narrower path in which I will travel down.
Well, if I was was to build a hull of that size, I’d make a trial section a foot long or so of the following: 5 oz kevlar, two layers diagonal planking of self-stick mahogany veneer laid crosswise to each other, 2 oz glass laid up over a male mold. Don’t laugh until you try it 
I’ll bet you’ll find it’s competitive in weight, more resistant to shattering and cracking than a carbon layup and possibly an equivalent amount of work, since you don’t have to make a female mold. I do confess to having worked with carbon fiber cloth once and having found it to be a miserable experience.
Cheers,
Earl
I tend to agree with Earl. I wouldn’t see much benefit in using carbon, unless you have a very effective vacuum bagging set up.
Someone else mentioned to me the other day, a lay up on a male mold with a much heavier glass cloth as the top laminate. The heavier cloth could then be sanded agressively to remove the slight imperfections often apparent when using a male mold - without sanding through to the next laminate (which in this case was kevlar). The sanding removed much of the weight of the top laminate and gave a really tidy finish. The strength of the top laminate was not required anyway.
I haven’t tried this myself (I’ve always used light glass as the top laminate). Just something to consider.
I have used male molds on both hulls I have made. The first was 1 layer of 5.7 oz glass and 1 layer of 2 oz glass as the top layer. The other hull used 2 layers of 5.7 oz carbon and 1 layer of 2 oz glass. They were both vacuum bagged and turned out very nice. Admittedly the inside of the hull looks alot nicer, but I can deal with that. My thought in going with a female mold is that the inner structures can be made an integral part of the boat and “laminated” in between the layers making it stronger. I am not nec. looking for a “competitive” weight because this boat at this time doesn’t have any competition. I am making this as a fun boat for myself and a stepping stone to a large CBTF boat, probably based off of the same mold.
Even at 61+ inches, you could use the scantlings of a modern Marblehead.
I don’t see that much of an increase in stress between 50 inches, 52 inches and perhaps 61 inches. I may be wrong, and have mentioned before that most of the hull skin is to keep water out - not to provide on board rides!
Keep the strength and overbuild near the keel box, assure you are transferring stress out to the skin (hull) and stay light on the skin (hull) for the rest of the boat. After all - this is a small boat without added weight of you as skipper !
Just a personal thought
What is the total weight going to be? This will be a factor in hull layup weights.
As an example, my International A class hulls (1.8 metres long and about 14.4kg - approx 70" and 32lb for you backward lot!) have about a 400 gram cloth weight (14 oz)
Plain glass is fine at this weight, carbon obviously stronger. Iuse both male and female moulds, hand and vacuum layups