Coosa

[RobCiminieri]

Has anybody ever substituted an entire build with Coosa rather than plywood. Been looking to build a completely composite boat. Been reading about coosa and I noticed the product has the same strength as plywoods does not need reengineering in regards to sizes and does not absorb residence like other composite materials. Any ideas?
Thanks

[fallguy1000]

Have you done a financial budget?

Weight budget?

Coosa is too heavy and too expensive to build an etire boat.

I bought a cheaper competitor in 3/4" and the board was about $350 with freight across the entire order. But let's say $320. That is double the price of other cores.

Then the density of most coosa is about 5-6 times other boards. Why would you take a hull that weights 1000 pounds and switch to a coosa core and increase the weight of say 250 pounds of core to 1250 pounds of core and effectively double the hull weight?

[RobCiminieri]

I am looking to build a fully composite hull but foam cores suck up resins. I am looking at options.

[BB Sig]

Copied from the pinned thread in this sub-forum.

Many ask for a foam sandwich version of my plans. It is correct that many of my designs can be built in foam sandwich and I know the material well: I designed for foam sandwich well before plywood-epoxy.

A good foam sandwich version of my designs will have the same hull shape and be close in weight but many parts must be recalculated.
The foam sandwich boat will use more layers of glass, use a different type of resin (SilverTip), specific types of foam. The hulls will be thicker, the framing spaced more widely and the gull assembly different.
I want to redesign the boats for foam sandwich and supply good building instructions.

Except for a few boats (PH15, LB26 and maybe some others that I forgot), there are no official plans for foam sandwich boats. For some designs, I have given specs to a few builders but I prefer to offer complete plans for foam sandwich versions with a nice shop manual. You can't simply switch the core type, there is much more to it if you want it done right.
I am almost ready with a very detailed foam sandwich shop manual for small boats but I have to work more on the layout, change some pictures then proofreading. It is already between 35 and 100 pages depending on the size of the drawings.
There will be more than one manual.
The first one will cover small boats built without a jig.
The second one will be for small to medium size boats built on a jig. Later, the third one will be for large units.
I started writing them as one manual 2 years ago and it was confusing, I had to separate them in 3 books with many common parts.
The plans will follow. There are differences: the framing is different, there are many high-density inserts and because of the thickness of the core many dimensions change.
In the mean time, this the traditional method to build in foam sandwich:
http://bateau2.com/howto/foam1.php

The manuals that I am working on will show a faster, easier method close to our plywood-epoxy boats.

[jacquesmm]

I am looking to build a fully composite hull but foam cores suck up resins. I am looking at options.

Foam core does not "suck up" resin. Those foams have closed cells. Cheap foams may suck up resin.
Coosa (there are different types) is not a good foam core.

[fallguy1000]

I am looking to build a fully composite hull but foam cores suck up resins. I am looking at options.

What drives the cost in foam core builds is the optimal methods result in a very low resin to glass ratio. This can be achieved two ways: infusion or wet bagging.

Wet bagging uses a lot of resin. Excess resins are needed for a rapid wetout so you can get the job bagged. Then the excess resins land in the media which results in the great ratio.

Infusion can use less resin, but infusion is a bit more complex. If you want to build with foam core; infusion is really the optimal way to go.

My build is all a wet bag build. I am too far into the job now to want to learn infusion; to change methods, and to change media, or even buy different foams. The right foam can be its own media, see.

If I were starting over, I would build a small dink with infusion, either panels or maybe the whole boat. Then I would translate that work to my current build and infuse the panels. Much less stress, lower resin consumption, and overall better product.

Now, let's say you ditch the fancier methods. You can, but you will end up with a higher resin to glass ratio, a boat of lower quality, and still use a lot of resin. I find most all my work is 1:1. That is, I mix the same amount of resin as the weight of the glass. Or 3 pounds of glass gets 3 pounds of resin. Lots of times we are in a bit of a hurry and the mix ratio might end up a bit higher on tapes for example, which we are not vac bagging. When I vac bag, that 3# resin becomes 2#s in the boat. A pound of resin ends up in the media; roughly. The media and xs resin ends up in the trash.

Anyhow, hope this helps you think through it.

[RobCiminieri]

Maybe i can start with a solo skiff. Would i just substute the ply sizes with a same size core? I am going to learn more about infusion. The foam process with the amount of resin is what always had me weighing options with the marina. I own a 1968 bertram bahia mar and i am always protecting the wood substrate. I am looking to try and built a totally composite epoxy hull

[pee wee]

The way I read it you don't just substitute foam for plywood, it is handled differently:

Copied from the pinned thread in this sub-forum.

A good foam sandwich version of my designs will have the same hull shape and be close in weight but many parts must be recalculated.
The foam sandwich boat will use more layers of glass, use a different type of resin (SilverTip), specific types of foam. The hulls will be thicker, the framing spaced more widely (?) and the hull assembly different.
I want to redesign the boats for foam sandwich and supply good building instructions.

You can't simply switch the core type, there is much more to it if you want it done right.
There are differences: the framing is different, there are many high-density inserts and because of the thickness of the core many dimensions change.
In the mean time, this the traditional method to build in foam sandwich:
http://bateau2.com/howto/foam1.php

The manuals that I am working on will show a faster, easier method close to our plywood-epoxy boats.

[Fuzz]

Hang on for a little bit. JM is in the process of writing a guide to building with foam. I am sure this will answer tons of questions for folks.