Thermo-Lite Boards

to build an entire Cat Project? Is it feasible?

I really want to build my first boat. Learned about Thermo-Lite and am thinking that stuff is ideal. Especially using the Supreme and Tough versions for the bulkheads, stringers, planking. But will it be as strong as a plywood built boat?

And how would that throw off the boats design? Thermo-Lite boards are lighter than plywood. Does that just mean more gear?

Thanks in advance,

Will

 

Welcome to the Forum Will.

We're going to need a whole lot more information.

What's a "Cat Project"?
Do you have plans already, if so, what material do the plans call for?
What's your Statement of Requirements (SOR)?

Being your first build it should be a sound, well proven design that meets your SOR.

Tell us more...

 

Well, yes I have study plans for a Ply/Epoxy build 42ft that will meet all my needs. K-Designs Manta. I will probably liveaboard much of the year, do a bit of fishing. Eventually venture out to bluewater when I have the proper experience, gear and crew. It will be junk-rigged so It can be short-handed. Displacement empty is 5 tons full 8 tons. Is that enough info?

The big head-ache will be insurance since I am new to boating, I will have to get a survey and take some sailing courses, etc... These Thermolite boards seem like an interesting material to build a new boat? Or am I crazy?

 

Its off brand coosa,

Coosa is a lot like plywood in physical characteristics, although ply takes a fastener a bit better. That and ply is way less heinous to sand/grind/cut.

Good for transoms, good for heavy bult boat decks. Not sure unless were talking sub 1/2 inch I'd like to bend around forms a lot of that density foam.

 

Yes, you could use it. My understanding is some builders do for everything from the hull up, but this would be for power/fishing boat builds.

I don’t know of a sailboat example.

The different densities and thicknesses make it easy to create contour. Once you’ve created your shape, you can add a few layers of glass to create rigidity.

There are recommended bonding adhesives that can be used to speed up construction.

The main advantages would be that it is lighter, doesn’t absorb water and won’t be epoxy thirsty like ply, and it is ready for epoxy paint or Gelcoat. I would get the smooth finish to save on fairing and surface prep.

One major disadvantage is it is hard on cutting tools.

 

Thanks for the replies guys,

That is sort of what I was thinking, Coosa/Thermo-lite isn't as rigid as Ply but it can be used as a core with glass to stiffen the structure. The idea of a low maintenance, 'wooden' boat appeals to me. But it will be a steep cost. The idea of saving time also appeals to me. Also, saving a ton or two of weight.

 

A photo for reference:

This is a 4x8 sheet of 1/2” ToughLite in 30lbs density deflecting under its own weight.

Not as rigid as ply, but it more uniformly bends because it is more consistent in construction.

 

You are choosing a material before having a design. That is a recipe for disaster. The Statement of Requirements (SOR) is always the first logical step. It is a list of everything you want. The constraints are in a separate category. They have to be compared and assessed if they can all coexist. Some may have to be deleted or modified. Once you have that, all the rest of the wish list can be worked on. Anything on the wishlist that conflicts with the constraints has to be deleted. At this point, you are ready to start designing (not drawing necessarily). The material will be determined by the SOR.

 

I have a design, it is for ply/epoxy/glass construction. Just thinking about an alternative to the ply piece. I mentioned it above. Thanks

SolGato, that pic above. Is that material similar to Coosa/Thermolite? And is it glassed?

 

I feel like a broken record repeating this, but here I go. Coosa and consorts are not plywood. They are a good substitute for plywood only where the plywood was used as a high density core. It's popular because it allows repairs without calculating new glass skins, a thing most amateur and professional repairers don't know how to do.

A ply catamaran isn't designed with structural glass skins, the wood itself takes all the loads. The glass is always cosmetic and might also not exist at all. It takes a complete redesign of the structure to a cored construction in order to be able to use foam, and once you do that there isn't much use for the high density stuff.

 

Ah Rumars, So It wouldn't work in the case of a high displacement Catamaran? Hmm, That is what I needed to know. Perhaps it is best to use this as a ply substitute in smaller craft?

Thanks, you just saved me from going down a very wrong path.

 

It's not about displacement or size of the boat. With very few exceptions plywood boats are not designed as cored structures. Plywood is like monolithic glass, a laminated structure, just a lot lighter and stiffer. You can't just substitute the plywood with foam it doesn't work that way, you need to recalculate the entire structure. Once you do that you realize high density foams are only needed for specialized applications and much lower weight foams can be used for the majority of the structure. The result is that you end up with the usual 60 and 80kg/cum foams that everyone uses and save a bunch of money and weight.
If you want a foam core boat buy plans for one, or have the NA convert them.

To put it bluntly, if a building was designed to use 4 inches of reinforced concrete for the walls would you use 2x4's and osb instead without consulting a structural engineer?

 

So I should stick to the original boat plan then. Which is fine. I thought this stuff could solve a bunch of different things but I will probably not have any issues as long as I seal the wood properly, glass properly and epoxy/paint etc. For interior and or non-structural I guess I could use something lighter but at that point the lower cost of wood is probably better. It would have been cool to have a lighter boat without any compromise. But I think I want the strength as designed.

 

You have to line by line compare the datasheets for Thermolite and say Meranti and Okume plywoods. And Rumars has grabbed Flexural Rigidity as the sore spot. But I don’t even see Flexural Rigidity on their datasheets. They show Flex Strength, but that is something else, iirc. So, flexural rigidity is something that is a likely issue.

I do see another problem, though. The lightest core is nominal density of 13 lbs/cuft which is more than 3 times the weight of typical marine foams used in hull making.

They do show higher density products which is good, because for transoms and engine bed stringers, coosa like boards shine because you can really put a thick skin on a glue up and build a waterproof and strong laminated core that can withstand bolt pressures for engine mounting. The transoms on my cat used a foam product called corelite. Do it again, I’d have used coosa, but the transoms on my boat have 8 layers of db1700 over the top and have performed well.

So heavier than foam core and less rigid than ply and probably pricewise comparable to ply, although, most coosa costs more than ply as well.

It is not novel. A few people have made monohulls with coosa and used it as a hull skin. It requires some research to get the skin thicknesses to the proper thicknesses so they are comparable to say okume. This is done by stepping up skin thickness and experimentation. You take a piece of each product and say the hull calls for 6mm okume with db1200 skin. That laminate is made into say a 6” strip and cut on a tablesaw to 5” by 40” or so. Then a piece of say 20# density coosa is skinned with db1700 same way and then you deflection test it after cooking or waiting a week with a point load and measure each. Finding the correct core/skin combination takes some extra efforts..

 

Hmm, sounds like I should call the manufacturer, see what they think of my Cat project and see where best I can use their stuff. Since I will be in the tropics, mainly. I think using board like this might be a good thing above the water line. Perhaps as deck and roof? I'd still glass and epoxy it in. Seems after a while epoxy will let in air, and damp sea air above the waterline can and will expose some of the wood core to rot. Thermo-Lite is very popular in Hawaii, for instance.... The beams on this project call for laminated Okumee ply, I wonder if I can use laminated TL, Glassed and epoxied, there? Would bulkheads be ok to use TL? The plans call for Cedar stringers and I think Cedar is rot resistant?? Above waterline Hull Planking? I need to talk to their tech people I bet...