Con:  Air is lighter than foam.   There has never been any reported sinkings of any Kaholo.  The best way to insure against being put in a bad situation is to stay on the beach.  Now that would be just silly.  So just follow the well proven building plan and enjoy.  Also, carry a flare.

First air can be replaced with water and foam will still float even if gets saturated.. 

Secondly, if you aren't adding something useful to the thread don't go out of your way to be a troll and

post something that makes you look like a smart ^$$. This kaholo of mine is going to be put through

Some pretty hard use and it's just another step I can do to make it safer. 

Hey, jmt2404, I'm not trying to be any of your profanity words.  You are on a site where people respond to questions and statements.  Hope your day gets better.

Adding foam will add weight to the SUP. Also if water were to infiltrate the interior, the foam would make drying the SUP out harder. The interior partitions are open to either increase air circulation, allow water to level if it infiltrates, or to lighten the total weight.

Even dories or kayaks that have added foliation, only use a small area within the hull for the additional foliation. The wood should naturally float. But additional floating might help broke parts float higher.

you might want to consider adding foam to the first 2 partitions of the bow and the last 2 partitions of the stern. That should be a good compromise.

Here's a step that was recommended to me by Larry Froley, the designer of the Kaholo:  put EPS foam behind the #10 bulkhead and flush it to the top of the bulkhead.  This will add strength to the underside of the deck should you fall on it.  Cut slots in the underside of the foam in line with the drain holes in the bulkhead.  Coat the foam, including the slots, with unthickened epoxy before placing it into the board.  I suppose you could do the same to the bow.  Hope this helps.

2-part structural foam (the kind you mix & pour) is about 2 lbs per cibic foot. Make your weight decisions accordingly.

It is closed cell, so it will not absorb water unless the cells break down. It would have to sit in water for months to start soaking in any at all. If your hull is punctured, you'll be cutting away the wood and foam to repair it anyway.

Be careful when pouring the foam. Make sure that nothing is preventing it from expanding, otherwise it could tear your boat apart.  Best bet is to pour it into the hull, let it cure, smooth the top (a very messy job that will leave you covered in foam dust), paint it with thickened epoxy and glue the deck on.

If you do go the route of having a foam-filled glassed wooden shell, you'll end up with a very tough boat, indeed. Either half would get you home.

Laszlo

Thanks for all the replies! I'm curious as to how much weight exactly the foam will add. 

Peter or Anyone else know if eps foam dissolve with epoxy like it does with polyester resin? Seems

like eps might be the best for weight and price. It won't be as messy as the 2 part foam to ttear out 

either if need be. The guy at my local fiberglass store suggested that I fill the inside with 2 lliter

bottles after sealing the cap with silicone to save on weight and money. Just not sure how this

would help the strength of a kaholo like the 2 part would. 

Larry Froley uses eps foam regularly in the boards he builds, in the manner I described, so I would assume that it doesn't dissolve in epoxy.  Can't give you the same info about 2 litre bottles, though.  

Ping Pong balls,

2-liter bottles would displace water nicely, but they are not as strong in compression as structural foam. The reason is that they have a very much smaller surface area to volume ratio than the foam, and they are not in as close contact with the boat's structure. All the forces in a collision will be concentrated on small areas of the bottles, instead of being spread out over the entire surface of the foam that's up against the wood, so the hull material will move more and has a better chance of puncturing.

They also don't have as much redundancy. If you have 3 bottles and one springs a leak, there goes 1/3 of your flotation, vs just losing a few hundred foam bubbles out of several million. That's why Locky's idea of ping pong balls is a good one.

However, bottles and balls and eps foam chunks have to be glued in place to keep them from floating away if the compartment is massively damaged. Foam will stick to the wood and good luck getting it out.

All those other substitutes will work to some extent. They will very probably be good enough since the possibility of an accident that is that damaging is pretty small. But by that logic, you might as well just leave it a hollow airspace. If you really want sealed flotation spaces that can't swamp, 2-part structural foam is the way to go.

FWIW, my approach to a really robust hull is to glass it inside and out. The interior glass provides strength in tension and does more to stop a hull penetration than exterior glass. Heavy bidirectional glass, not woven, is the strongest, but 6 oz woven is good enough for small boats. It's also lighter than completely filling the boat with foam. I've used the foam on a couple of boats, but only in compartments that are likely to be punctured in bad accidents.

Good luck however you go,

Laszlo

Locky, that's going straight myth busters style! Is a good idea but I don't have a cheap access to a 

hundred ping pong balls. 

Laszlo, what do you think about a combination of the 2? Eps foam in the front and rear ccompartments that 

will give me the structural reinforcement that I want and in the center compartments use the 2liter bottles? 

I am thinking wrapping the eps in packing tape or Saran wrap before glueing them in there might help 

keep the pieces together and save heart ache if I do have to tear it out. 

Also I am going to "tab" my joints (scarf joints and butt joints) with the extra 4 oz scraps I have left over 

to add A little more strength to the joints. Ill be using the wet on wet method of tabbing them in to 

make sure it's a good bond between the fillets and 4 oz cloth. 

Oh and I do agree 2 part foam would be the best but for weight and price I can't bring myself to do it. 

The Kaholo has a closed deck and ordinarily requires some means of venting to prevent trapped, expanding hot air from busting out the seams of your carefully crafted craft.

I would be concerned that closed cell foam would compel this situation in the worst way. Even with some sort of vent, expanding air is not going to be able to migrate through the foam.

I glassed my Kaholo inside and out- primarily because I stripped all the parts instead of using plywood- and used a double layer of 4oz on the underside of the deck. It feels pretty durn solid and has taken a beating this summer. Punctures/leaks seems most likely to occur near the numerous hazards by the shore, not in the open (liquid!) water. And you really should be wearing a pfd, anyway. I'd skip the foam and beef up the glassing schedule if you're extra concerned. But I am by no means an expert.

Good luck,

Patrick

Patrick, I completely agree with you that the foam could only complicate things if done in a way that wouldn't allow the air to vent. But I don't think it's going to be a proble, with the way I plan on doing it. (Only putting foam in the front and rear of the board) there won't be any air on the ends of the board that would be trapped and away from the big cavity in the middle. 

Have you weighed your board? I'm curious to know what it comes out to. I have some VERY thin surfacing glass ill be laying down when I waterproof the inside that should provide a little strength. It is supper thin though. I'm not sure of the weight but to give you an idea, if you took 4 or 5 layers of it on top of each other then it might add up to the 4 oz cloth. It's really thin. 

Aye- but there's the rub. The foam itself is trapped air- thus "closed cell." The foam will expand and contract somewhat. And since it's not loose and flowing (like, say, strofoam peanuts) but stuck in place, you could still have problems, albeit locally. If you're committed to the idea perhaps you could add the foam prior to installing the deck and dam off the foamed area so that it will not be in coatact with opposing sides of the craft.

Haven't weighed the stripped Kaholo- we don't even own a bathroom scale so I don't have a practical way to do it. I'm guessing that any additional weight is due to glassing the interior so rigorously- something I'd do again in a heartbeat. I have no trouble cartopping the board by myself, and once I'm on the water I'm not concerned wiht an extra pound or two. I am by no means a fiberglassing expert and am not familiar with the style/weight of glass you're referring to, but I would imagine there is a point where going lighter offers no practical weight savings and yet does suffer loss of strength. The epoxy is a significant portion of the added weight. So for instance, you might end up using nearly as much epoxy to wet out your super thin stuff as you would if you'd have used 4oz, but the very thin material might offer substantially less strength than the hypothetical 4oz. Remember there's little reason to fill the weave on the inside of the craft. There are many on this message board far more qualified to speak to that notion than I.

Good luck!

Patrick

Right on, I agree about the thin stuff not adding much more strength, but it's all I have that's light. The 4 oz mat is just too much money for me to glass the inside of both boards I am building. I will be using the 4oz scrap pieces to sort  of "tab" in the all the joints. 

The stuff inside the closed cells is not air, it's gas that forms when the 2 parts are mixed. The millions of dead gas spaces make an excellent insulator, so a thin outer layer may heat up, but the vast majority of the gas will not. It's also an exothermic reaction, so the gas inside the cells shrinks when it cools down, but the cells are hardened by then.

Coupled with the fact that the foam has a very low coefficient of thermal expansion, there's pretty much no chance of a closed, completely foam-filled compartment bursting.

The dangerous situation is a large, uninsulated airspace with thin walls. Whatever other basis the decision is made on, fear of bursting is not an issue.

Have fun,

Laszlo

Interesting. Thanks for that good knowledge! 

I agree with Lazlo that your Kaholo is unlikely to “burst,” Michael Bay-style, but I’d still be concerned about expansion/contraction damage over time.

Over the course of a few weeks the blowing gas used to create those foam bubbles does in fact come into equilibrium with plain old breathable “air.” Think of a helium balloon that remains inflated yet sinks over a matter of days as its helium is diluted. The foam loses a bit of its insulating power in the process. Regardless, the foam is filled with trapped gas that will expand and contract with changes in temp.  Strap the board to your car on a nice day and the foam will heat up- insulation merely slows heat transfer, it doesn’t stop it. Now drop your preheated board into the relatively cool waters and the foam will cool down rather quickly. Unlike a solid foam board, the plywood shell and bulkheads will have different coefficients of expansion. These are certainly elements that can lead to joint failure. Whether it will happen before some other defect ultimately decommissions the craft- well, we’re all just guessing.

Me- I’m digging the ping pong balls.                                                         

Good luck!

Patrick

Ok well I am almost done with my first kaholo 14. (I'm building 2) I thought I might update you guys on the progress. I decided to fill everything but the 2nd cavity where the hatch goes with eps foam. And I have to say I'm pretty happy with it thus far. http://i1176.photobucket.com/albums/x340/jmt2404/image-1.jpg

here is a direct link I case my pic didn't work. There are more pics of the process of the board if anyone wants to see that as well. 

let me know what you think! 

I have a 40+ year old sunfish that is a bit overweight because eventually the interior foam soaked up some water. The recommended solution is to put two inspection ports in and create cross ventilation but placing a lamp near one. I believe the foam is in the form of bricks adhered to the inside of the hull, which permits some airflow. 

Just 2 cents. I think your method offers additional benefits in structural integrity.

jh

She will never sink with the EPS foam!  did you weigh the amount of foam you put in?  Just curious.  EPS foam in surfboards has a totally different feel than polyurethane foam, it seems more lively, more buoyant.  When new anyway.  You should do the other board with no foam at all for a nice comparison.  Good luck with both!  They are fun to fish from, I built two as well, one rigged for fishing and one for paddling.

I did not weigh the foam before I put it in unfortunately. I'll weigh it when I'm done to see the final product. I did leave enough room for it to properly ventilate any air that will be trapped. I used about a sheet and a half of 2" x 4' x8' foam from Home Depot. 

As for strength, I can already see a difference between the cubby hole in the front and the rest of The board. It doesn't flex very much at all where the foam is which is what I really was worried about. After I get the final weight of this board I will decide wether or not I will fill the second board like this. It is for my wife and I don't want it to be ridiculous. 

I would insert a couple of partially filled beachballs, forward and aft.  Pretty common in small sailboats like Opti prams.