expanded foam in hull question

Yet another question for you experts. I removed all the foam from my '86 Nautique and have reinforced the inside of the hull with additional glass cloth and resin -especially along the area where the chine meets the bottom. Stringers are good. I am going to replace the floorboards with PT plywood. Is that foam structural and does it have to be replaced? If so do I have to fill the complete cavity below my floor boards ( I know the original floor was glass over foam, which I removed). By the way, the old foam was soaked and weighed a ton! A situation I would like to prevent in the future. I also intend to glass over the new floor prior to carpet installation.Thanks guys.

Peter

I can drive a large nail into solid wood and the engine mount bolts are turned in tight. There are some cracks in the gelcoat along the chines on each side running about two feet about midship; one piece of gel is actually missing (about the size of a quarter). When I removed the carpet I noticed the glass floor had separated from the hull sides which prompted me to remove the floor and found the soaked foam. My guess is this allowed the gel coat to flex and resulted in the cracking. New floor will be glassed into the sides. Thanks for your prompt reply.

Peter

I know we all have discussed to foam or not a hundred times now but I have talked to and seen proof of that the foam does provide strength to the hull. It helps keep the bottom from deforming when hitting waves. The hull can be used with out it but you are more likely to have issues pounding in choppy water and this can lead to stress cracks. This was from a nautical engineer. I hate the water getting in the foam but I am re-foaming anyways because I have enough issues with the boat pounding as is.

if you look at it this way, was it put in for safety or was it put in for structure?
i would say it was put in for safety and the only minimal benefit would possibly be some structural quality in using it, it has no grain so its not for adding strength.....it has no use, if the gunnels were double walled like a whaler then pumping a sealed cavity i could see its benefits. it sounds like a double edge sword...in a CC its for safety in a Boston Whaler it is a combination of both

Peter, Are you adding the 2 layers of glass between the stringers because you feel it's needed for hull support without the foam? Just wondering!

Adding the luan is not agood idea. First, I don't feel it's going to add structurally and also luan is a very poor choice from the standpoint of rot.(just in case you get water in it)

Well, that was my idea. Overkill? or How can it hurt. Scratch the luan. The two layers would be between the chines down to the first stringer.

im looking at it a from a different angle cause i could think of 10 other ways to make a boat more structurally sound than using foam, it is required and the hulls were designed around its use, since it is required why not use it as part of the structure and build the boat in this fashion, lets skimp on real ways to make a boat sound and use the foam which is required and to some extent does add a compression factor and not a twist factor, im not doubting it as to be part of the structure, but because it was required it was used as an addition to the structure,
if the foam was not required then the engineers i would guess never would use it because of cost and tie in the hull in other ways and make the hull more rigid

captpete wrote: Your comments are helpful. I will check the bottom of the stringers this weekend. My plan now is to add two layers of fiberglass to the hull where the foam was ( what about glassing in 1/8" luan between the layers?) for strength. The boat will not be subjected to excess pounding if I can help it. I really can not see how new foam will not become water logged again. I will also use 1/2" plywood coated with resin and then the upper part, once installed, will be glassed. Interestingly, I really enjoy this working on boats! Most of my time on the water has been as a captain on my 31' fishing charter boat - of which I am now selling because of fuel prices. I guess this project is my "hot rod" that I always wanted to build in high school. Anyway, great being a member of this site! Peter

Quit half-assing the job and put new stringers in. Why do all of that work and not replace the stringers??

I guess I opened up that "can of worms" with my question on foaming! I appreciate all the feed back. My next go around will be engine related so get ready.

Capt. Pete

I thought about it for a while and if you take some 3/4 ply and build 2 boxes approximately 1x2x3 square fill one with foam and one without foam and with not knowing which has the foam, and jump up and down on them with your body weight, will you know the one with the foam? and if you make them both air tight and throw them in the lake will they sink???this all of course after you glass all the corners and epoxy both sides.
what would your answer be?

BuffaloBFN wrote: I say both would float and you would be able to pick the 1 with foam!

Yes you could tell the one with the foam only because it will float lower in the water. The foam is 2lb per cu. ft. and will add to the weight of the box.

I'll still say that the foam isn't needed as a structural component of the hull. Even though we have all seen some of the "engineering marvels" of CC through the years, I'd hate to think they counted on the 2lb density foam. 2lb is not a structural foam. The Whaler construction example is totally different. It is a closely spaced inner and outer skin both acting as tension or compression members. It's hull was engineered as a system.

Someone else besides Tim (was it you Greg?) mentioned months ago about the oil canning of the hull while walking in it stripped. You really need to consider that the PSI of a persons foot is a lot more than the hull sees sitting or running over the waves. The surface area of the hull really spreads out the boats weight.

We also haven't heard (maybe someone else has) about a older CC with soggy shot foam with absolutely no structure left causing a hull to come apart. Gel cracking yes but is it from bad foam or rotten stringers?

Pete, Eric said jump up and down on both boxes. I say the 1 with foam will be easy to pick out...by more than the sound. I'd even go so far as to say that whatever exact weight dropped from a given height that would break the empty box would not break the foam filled box.

Greg, I did see that Eric mentioned jumping up and down on the boxes but felt he was talking about doing it in the water. Eric - In the water? I don't think you could tell. a 2' X 3' piece of 3/4 ply is pretty stiff.

Now, as far as the drop test, I think we could use the pumpkin patch for it. What do you think? I'll pitch in for the crane!

Alright, I'll give in and go along with the foam being part of the engineering CC did!!

I remember I had a friend with a 14' Shell Lake with I think a 60 outboard on it. This was the very early days of glass. The hull bottom was so thin that on real sunny days you could see through it to the lake bottom. Talk about flexing when going over rough water! It was actually scary!

Besides...it's original?!!?