Foam catamaran kayak

Hello all,
This is my first post on this site. Am just beginning to construct a catamaran kayak mostly from XPS foam. The hull dimensions will be 12" wide, 16" high by 12' long. The out to out on the hulls will be 5'. I want stability. I want to get back out on the water again, and this will also be a good project to keep me busy [as I am retired]. Have had all sorts of boats from El Toro to 31 Hatteras Sport Cruiser, but have not had a watercraft in years. The kayak needs to be kept light and designed to be able to be taken apart, so to be car toppable [is that a word?]. The XPS will be from 4' x 8' x 1" sheets. The chines and shear will be strips of 1/2" ABA marine ply. The decking will be 2 each 3' x 4' sections of 1 1/2" Tricel honeycomb material. Planning on numerous foam blocking bulkheads along hulls. The deck sections will be hung between the hulls on alum conduit sized to slide into each other and secured by D rings. Propulsion will be by SUP paddle in emergencies and by NV 55lb [or 62 lb] trolling motor. Total weight is estimated at 600 lb [when 1st mate is aboard] which should require about 4.8" of draft. Wood to wood adhesive is Titebond 3, wood to foam or foam to foam is Hotwire's Foam Fusion. Have just finished a major camper trailer project, and unless the paint experts say differently, plan to go with 10 oz duck over the foam, glued with Foam Fusion, and then painted with Glidden Gripper and several coats of exterior paint. That is the design at the moment, but am always happy to change course due to new ideas. Look forward to hearing from you.
Glen

 

Welcome to the Forum Glen.
Do you have any sketches or drawings so far that you could post on here? As the saying goes, "a picture is worth a thousand words".
I am a bit baffled by quite a lot of your description.
You mention that the overall beam is 5', but the decking will be "2 each 3' x 4' sections of 1 1/2" Tricel honeycomb material."
I am assuming that you will join this such that you have an 8' long x 3' wide deck (resting on the aluminium conduits?) between the hulls, with the two 12" wide hulls making up the overall 5' of beam.
You mention using '10 oz duck over the foam' - what is 10 oz duck?
Will the 1.5" thick Tricel honeycomb be sheathed with anything?
I had to google foam fusion glue - do you think it will be waterproof enough?
Foam Fusion #028B https://hotwirefoamfactory.com/028B_Foam_Fusion_Glue.html
There was a thread on here recently where they talked about Titebond glues, and I think the general consensus was that they shouldn't be used underwater (I may stand corrected on this though).

 

Hello Bayansailor,
Thanks for the reply, and good questions. The photos are now going to be a longer out, as the cardiologist informed me today that I am to get a pacemaker next Tuesday. No picking up anything [including a 7 1/4" skilsaw] for 3 weeks. Yes, the decking will be 8' x 3' between the hulls, the top of the hulls will have non-skid on a strip of 1/2" marine ply [probably 10" x 8'] to distribute the load of the deck supports. Talked to the Tricel fellow, and there will be 1/4" Luan sheathing on both sides. Must figure out some way to waterproof the Luan. The honeycomb material is waterproof. Hope the Foam Fusion glue will not be tested for water as it will be within the hull construction, except for attaching the duck to the foam. "Duck" is the various types of cotton canvas; 10 oz is a popular weight, very close weave. Go to the "big duck" site for information, interesting history. The teardrop people and some foam kayak people use Titebond glues for various things. There are 3 types of TB. 1 and 2 are water resistant, 3 is said, by the manufacturer, to be waterproof. I have used a lot of TB 3, and once it sets, it is stronger than the wood itself. Still, have not tried a saturated test with it; hope it does come to that. The teardrop people still have not heard of Foam Fusion which bonds XPS foam to canvas and practially anything else. TB only sticks things which are porus. XPS is NOT porus. The key to keeping the water from getting into the glue or wood is getting a really waterproof barrier between the water and the canvas. The camper is doing very well with a skin of duck glued to panels of XPS [80%]] and 1/4" ply [20%] with FF, covered with Gripper exterior primer and several coats of exterior acrylic paint; but then I don't plan for the camper to go swimming.
Glen

 

A few random thoughts..

The whole thing needs to be epoxied and glassed in my opinion; more so if using inferior cores.

I have no experience with canvas.

xps needs special prep to glass; I have found sanding it with 36 grit and hotcoating it to be the best way for it to not delam easy

bulkheads need to be stiff, so plywood is hard to beat for stiffness to weight; of course ply would cut xps hull easily...

 

I would agree with Fallguy re using epoxy and glass, especially on the hulls.
And I am sure that this will be much lighter weight (not to mention stronger) than using 10 oz duck canvas soaked in paint to make it watertight.
As you say, the duck is ok for your camper because you are not planning on going swimming with it.....

Re the Tricel decking, it sounds like it is a sandwich with a core of 1" thick honeycomb between 1/4" thick layers of Luan - this seems to be a huge overkill in terms of strength surely? And it is going to be relatively heavy as well.
I am thinking that a 1" thick core with a layer of glass / epoxy each side should be a stiff enough sandwich for the deck application? What will be the maximum panel size that is unsupported between the frames?

I hope that all goes well re your pacemaker operation next week.

 

Welcome to the "non-voyeur", active side of the forum, Glen.

This is all good advice above, I concur wholeheartedly.

Good luck with the pacemaker, it beats the alternative.

 

if I understood correctly, you want to build something similar to what I built last spring, only a bit bigger. This is my creation, hulls are 3.75m long , 15cm wide, 30cm tall. Deck is 125cm X 60cm (dimension of xps sheets here). Total beam 1m. Hulls are solid xps insulation foam, 5cm thick,glued together with polyurethane glue. On deck and bottom of hull is used 3mm poplar plywood. Hull completely covered with 300g glass and epoxy, painted with 2 part polyurethane paint. Deck is one sheet of xps sandwiched between 2 sheets of 4mm poplar ply, coated with epoxy (no glass on deck). Crossbeams are alu square beams 25mmx25mm. I inserted 25mmx25mm wooden blocks in the hulls where the beams connect, in order to have something rigid for the screws to attach.
It is very stable and fun for messing around, I get dive from it and get back on with a ladder on one hull..... BUT I would never build it again... it's too heavy, it takes ages to shape/glue/protect the foam..and you need to build a plywood box to give it strength, so you might as well just go with a simple plywood hull. In the water it was very heavy to paddle, it just didn't flow well. I built it as a paddling platform to be able to paddle in a sitting or stand up position, but it was so frustatingly slow and heavy.

 

forget to attach images...

 

Welcome Glen.

Tough one with the pacer.

I think this is a great project for you and your health. But my 30 years as an industrial painter and 5 years repairing boats professionally gives me concerns about your plan.

Using inferior (non-marine grade) materials yields inferior products. IMO, painted canvas over XPS is a beach toy not a proper boat! The materials you have listed will start to deteriorate in less than two days of constant immersion. If you want a durable craft, forget about latex primers, bypass interior (luan) plywood, skip cotton skins, and rethink the use of XPS.

You are already planning on a thin plywood exterior. Why not use 1/4 exterior or 3mm marine ply alone as the structure? There is no structural need for the foam in your plan. If you want "post catastrophe" buoyancy, drop some XPS into the floats before sealing them up.

Pre-coat the plywood will epoxy. Join the seams with fiberglass tabbing tape. 6 oz fiberglass twill epoxies overall. This will yield a vessel which will last. It's the same amount of labor and only 10% more money.

Good luck and heal well.

 

And the best pun of the day goes to BlueBell!

There are a number of reasons it is slow, but the heavy point is a good one and probably primary.

The hulls are displacement hulls.

The advantage of two hulls is not apparent and probably a detriment.

The hull exits and entry into the water have visible drag issues.

How heavy is each hull? Edify the OP

300 gram glass is pretty thick... I would think 6 oz would suffice..perhaps 2 layers on bottom..also there is little need for ply on the bottom..

 

I never got to weigh the thing... but handling it i'm guessing around 40kg, based on comparison from the canoe I had before that I knew weighed that much.
I could probably gain a little bit of speed if i gave a bit of rocker at bow and stern, but working with foam was such a horrible experience, that I just don't want to touch it any more... i'd rather build from scratch 2 plywood hulls, using the foam only as bulkheads every x cm so it gives me some emergency buoyancy. But this thread is not about me, it's about the advice I can give the op about building a foam hull..:
- it's going to take more time than you think
-it's going to cost more than you think
-it's going to be heavier than you think
.it's going to be messy... very messy shaping foam.
but you won't trust me, just like I didn't trust the tens of threads I read before building it , and went ahead anyway... If I was using it to fish , it would be perfect, unsinkable, stable, and up to now (6 months always in the water, unprotected from the weather) it is as new, no delamination.

 

That loo0ks almost exactly like one I designed a number of years back except I tapered both ends of my pontoons. I made the pontoons according to set of Quick-Ama plans. I built a 1/4 scale model of it and tested it in the bathtub and it did almost exactly what the calculations predicted. I can't remember, but I think mine would only have weighed about 50 pounds. I never did build a full-scale copy of it.

 

Best wishes for your health, and that pacemaker may have saved you from some heartaches later. I concur with the others who've commented on your unconventional material choices. I'd be very afraid that the second time you went to put it in the water you'd find that substantial portions of it had turned to sponge. If you still want to build one, please make it out of real boat materials.

If you decide you'd rather just buy a boat and hit the water, there are these:

Wavewalk® Stable Fishing Kayaks, Portable Boats and Micro Skiffs – Wavewalk stable fishing kayaks, portable boats and skiffs http://wavewalk.com/blog/

By all accounts they seem to perform quite well, but the earliest versions tended to flex and eventually crack. The manufacturers did redesign them, but the current models still flex, and I don't exactly like the wooden brace they came up with to stiffen them; it seems too much like a kluge to me. I also don't like that they seem to encourage people to drag them everywhere, including over sharp rocks and broken concrete. They also need sealed bulkheads instead of their suggested pool-noodle flotation.

People have copied their design in plywood and also done similar plywood boats with variations on this form, but not all of them work out.