Foam between stringers?

63Electra

Seaman
Joined
Jul 20, 2019
Messages
51
When taking out my floor and exposing the aluminum stringers I noticed that there isn't any foam of any kind. When watching the infamous YouTube on replacing floors, I see that a lot of boats have foam between the stringers. Is this a manufacturer thing that not all boats require? Is it a good idea before reinstalling a floor that I should use some kind of foam? I'm building this boat to last and want to do it right the first time. Any help would be greatly appreciated.

This is on a 20' X 8' aluminum hull.
 

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AShipShow

Lieutenant Commander
Joined
Jul 8, 2016
Messages
1,803
USCG requires flotation for boats under 20' in length, so my guess is your boat is slightly over 20' so it was not required by the manufacturer to add flotation. The other possibility is it was removed by a previous owner.

In boats with wooden structures, there is a constant debate on whether or not to rebuild with flotation foam. One school of thought is, if the foam is left out, it won't hold water and cause premature rot of the structure in the future. The other thought is, if the boat is sealed properly with new fiberglass and resin, then the structure should never get wet and the foam will make the boat comply with USCG rules.

One other thing to note is, the expanding 2 part foams also add a fair bit of stiffness to a new deck that otherwise may have required a thicker wood to be rigid enough.
 

emoney

Commander
Joined
Jul 19, 2010
Messages
2,551
I would vote for adding foam, if for no other reason than what Mad Props mentioned in strengthening the deck. Couple that will any "just-in-case" scenario for flotation and now you've doubled the reasons why. It can be purchased directly from an Ebay seller for quite a bit less than some of the National Chain Marine houses and isn't a difficult thing to do. You can never be sorry when adding extra precautions.
 

63Electra

Seaman
Joined
Jul 20, 2019
Messages
51
Well I can't seal off the deck since my boat is alluminum. I can fiberglass the floor but not to the walls. So my concern is that if I used foam it might get debris trapped under my floor like sand, leaves, dirt and stuff like that. However, I'm not sure how I would clean it out even if I didnt have foam so...

I have no problem using foam at all! I just didn't want to add something that would retain or trap water. Is the foam an expansion type of foam? And if so would adding PVC pipe throughout the hull be recommended to allow flow to the bilge?
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,802
Foam can be poured in place as part of the structure of the boat.----Different densities are available.------The WINNER boat brand in the 1970's used plastic containers ( size of a small loaf of bread ) for floatation.----Doing an ACTION MARINE 17 right now.----Water logged foam is thrown out.-----Installing composite hockey sticks as extra ribs / structure.----Composite hockey sticks for the transom.-----This boat will be very strong and transom will not rot again !!------But the location / size of lake / water temperature / availability of help from nearby boaters all factor into the decision making !----Just my opinion. on the matter.
 

kcassells

Fleet Admiral
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Oct 16, 2012
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8,739
Racer this is what popped into my mind with your name title.....
th
 

kcassells

Fleet Admiral
Joined
Oct 16, 2012
Messages
8,739
Forevea if its dry! Just remember if you have to trim it for any reasons then the close cells become open cells. Seal with polywantsacracker or EEEpppoooxxxyyy to seal .
 

chevymaher

Commander
Joined
Mar 29, 2017
Messages
2,937
How long does the 2 part foam last?

Mine lasted 30 years. Wood was gone it was only structure the boat had left. And it still worked fine when I took it apart.

Think of the difference of beating on a drum. And being in a soundproof room. That is how ridiculous the difference is in the boat. Stronger absorbs vibration from the pounding waves. It is quiet.

Screw the I am going to live if it fills with water. Those 3 things listed above are more than enough reason to use it. A boat that wont sink is just icing on the cake to a boat that rides and is quiet like a caddy on the water.

I added way more than it originally came with. If i ever do another boat I will be adding it in any place I can.
 

63Electra

Seaman
Joined
Jul 20, 2019
Messages
51
I'm worried about drainage tho with poured in foam. Ok ok....dont laugh but I have another idea. I have watched people raise boats that have sunk by pumping ping pong balls into the cabin. What if the hull was completely filled with ping pong balls? Lol water proof, great flotation and air can get under deck to dry. šŸ˜‚šŸ¤£
 

steve_h7

Chief Petty Officer
Joined
Sep 16, 2018
Messages
401
No drainage needed in the sections with foam.... they should be sealed with no possibility for the foam to get wet or a need for anything to "dry".
There's a lot of empty space between the balls. In a catastrophe I'd rather not possibly have to trust my life to ping pong balls.
Just my 2 cents...
 

chevymaher

Commander
Joined
Mar 29, 2017
Messages
2,937
On my boat only place the water got in is where there was no foam. If it was full of foam the foam was dry. And my boat was the poster child for How not to care for a boat. Literally full of water when I got it. Had to poke the bilge hole out to even get it to drain.
 
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