The pink stuff......

[Oscar]

OK, I have my nomex suit on, ready for the eternal flame job I may receive......

Closed cell foam with fancy names like "eternacell" is a core material. Light, strong in a laminate, impervious to water and it plays nice with epoxy.

So does the pink stuff from my local home improvement house of worship. I did some testing and it holds up perfectly with resin and cloth on it, gets strong enough for what I want it to do (a few bulkheads in my ama's) and a 2'x8' sheet an inch thick is under $10, which is a fraction of the "real" stuff. Lastly I'll paint it, so no one will ever tell.

Is there any reason NOT to use it?

[stone]

I dont see why not. Although my choice would be 1/4" or smaller plywood. I am curious as to why there are even bulkheads in there in the first place. How big are your amas? My 18' and 16' catamarans have no bulkheads.

[Oscar]

They are 21 feet long.

There were no bulkheads. I am putting them in to A: Increase stiffness somewhat. B: Create 4 water tight compartments. If you hit something at 15+ knots you may well put a hole in it. I sail day and night, and sometimes quite a few miles from dirt. It's insurance. (And cheap at that.)

[Oscar]

No one else wants to touch this? Or is it not worthy of discussion?

[stone]

You may already know this but the problem with multihulls especially performance multis they suffer greatly in performance with any extra added weight. I think you may be over thinking this one as the amas should be stiff enough as they are.They are balsa cored ,right?
To give you some perspective, on my 18 which btw was raced very hard and is now my main beach ride its laminate schedule is very thin with only about 5/6th" 2lb denisty foam core with only "good enough" vanilla ortho polyester resin skins. Still the hulls are extremely light and stiff with zero oil canning or flexing. This boat lives on the beach year round and is sail extremely hard in and out of the surf dragged up and down the beach,etc.
The hulls do have a block of foam in there for flotation, and it has come in handy several times. In fact in this pic my dagger was jammed into the back of my hull after I smacked a sea turtle . (You can also see the deck cut out with the thin skins and core)
Another idea to increase stiffness would be to add latitudinals and longitudinals foam beams. But I would think this would have already been done it it was thought necessary.
If you are dead set on adding bulkheads then fine if it makes you feel better but again IMO I dont think you need them. A simple foam block will do the trick .If you really want water tight bulkheads then the glass over plywood would be a better choice.

[Chris Campbell]

Not knowing whether or not there is a reason to avoid the pink stuff would be enough to keep me away from it, I think. Especially given the amount of work you're putting into this boat to rebuild the amas - is the cost of the pretty small amount of foam core you'll need to create some bulkheads worth skimping over? How much will it actually cost to get the 'right' stuff?

If it was me and I had as much time and money invested already I'd splurge for the fancy stuff. You might even find some scraps somewhere at a discount - I'm sure that bulkheads in your amas will be pretty small, no?

[preserved_killick]

I know little of about the end use you are dealing with, but I can say this about the big-box store cheap pink foam: it works well for surfboards. Surfers are rough on stuff, boards are easily broken and are so all the time. I've known guys who have glued up some of that hardware store foam and build surfboards out of it. It appears to hold up as well as any blank out there. It needs to be painted since it looks ugly, but no one complains about the strength.

[Oscar]

Thanks all for your viewpoints.

I put the bulkheads in, and they've come out very nicely, I think they will do just what I want them to do, which is to divide the floats in separate chambers to increase safety, and to add some stiffness. They've done just that, with almost no added weight. (a few pints of resin). All compartments will have inspection plates for drying, one will have a hatch for storage of light stuff like fenders and a boat hook. In that compartment the pink will be painted a nice bilge grey.




I have also decided to build up the deck with foam. The hull to deck joint was created with thickened polyester and an inside upside down shoe box. The deck is also a balsa laminate and to restore it to it's original condition would pretty much require starting over. The joint is compromised in quite a few places.

The edge stands proud by an inch. I can fill with resin where open and then rivet through there every ten inches and add a mechanical fastening to the joint. Then put foam in between the edges and glass over, wrapping around the outside edge. This will in fact create a new laminate with the existing deck being the bottom layer. It will stiffen and strengthen the whole thing and, very important make it waterproof, as the myriad of cracks in the polyester now are not. I'l prep the deck with a good 60 grit grinding and remove all the anti skid, down to the glass which should give a good base.

This photo shows the concept. Needless to say all will be formed and faired.




The ama's were built light, but not to last, on top of that they were not maintained properly. Damage to the outer skin, and resin starvation of the inner glass layer, combined with the boat sitting on a mooring with water in the floats has led to water intrusion and rot. The hulls are solid and strong again, the deck will also be better than before, and in the end it will all look good, and last for many more years. After removing the wet balsa I will be at a net weight loss. Stripped they weigh in at 135 each now. With beams and hardware about 230 a piece.

Maybe some day I will take the best one and use it as a plug for carbon fiber new ones..... Fortunately the center hull is solid. (as in not cored.)

[The Froon]

Can you describe with some detail the installation process for the foam bulkheads? Did you leave a space between the foam and the hull as called for with marine grade plywood bulkhead installation? Did you create a fillet, then tab the foam in place. Did you fully cover the foam with fiberglass and then tab it onto the hull?

Thanks,

Brian

[Oscar]

I cut the foam as close as I could. It is flexible and thus needs no gap IMHO. (People use this stuff to fill the gap on wood bulkheads). I then traced it on the glass with a big red magic marker, and cut three inches wide. Then I cut in to the line every 5-6 inches to create the tabs. I "jammed" the bulkhead in there (into the taper of the hull), "painted" it with resin and put the cloth on, further wetting out where needed. The red marker tracing helps slide the cloth into the right position. I cut ribbons four inches wide, with lateral cuts every 5 or six inches and put a second corner in there after it all was tack free, this time with the uncut part on the hull and the cut tabs on the bulkhead (This way there was a solid piece on both sides of the corner). No fillet.