Advice sought on catamaran keel building

Hello:

I am building a custom foam/glass micro cruising cat (sailing). 27' by 14.5'. Have decided to build LAR (fixed) permanent keels. One on each hull. Approximately 23" deep by 5'2" long.

My plan at present is to use very thin marine ply (say 1/8") to carefully make 2 identical "foil shaped boxes" (without a top and just two curved sides). Use that as the "core" and the start laying up triaxial glass/epoxy to a pretty thick structure on each side. In the end the ply core is not really relevant...mostly glass. Add more glass at the bottom and leading edges of course and leave less near the top.

Glue onto hulls and start to add more glass/epoxy to tie in with the hull. In my design I have 2 pretty substantial bulkheads in each hull that can extend all the way down to the very bottom of the keel, so I think using those to tie the keel into the rest of the boat's mass would be the way to go. Screenshot of those bulkheads extended down is attached to this thread.

Looking for any opinions on this...has anyone done it? Things to watch for? Advice on thickness of schedule very much appreciated as well..

Also, links to articles or previous discussions on this type of build, especially with pics, welcome....

Thanks..>>>

 

You will be adding almost 40 square feet of wetted surface area if you do what you propose. Performance will suffer some as a result of excessive WSA. Also you will be constrained to put the rig wherever the "keels" force you to put it in order to achieve suitable helm balance. That might become problematic. I can not swear to it but I suspect that the boat will not turn as readily with both those keels immersed at the same time.

 

Keel placement (as previously mentioned) is critical to sailing abilities. You can't really guess, they have to be right or you'll be moving the rig and all of it's attachments. So, you have to decide which you'd prefer to have to re-position. If the rig is in place, the obvious choice is the appendages. Without a clue about the current design, it's rig and appendage arrangement, the best advice is, sure your ideas sound fine, assuming the appendages are appropriately placed, under the existing rig. As to laminating schedules, well again, we'll need some additional design information. It's a bit like asking what engine to use in your car, without knowing what year, make or model it is.