How much floatation foam do I need?

[72cheyenne]

Hi everyone. I am redoing a 1983 Nordic Crestline 16ft runabout. I have the floors out and want to replace the foam in the bottom because it's all water logged. It runs full length right down the middle and on both sides. Does anyone know how much I would need to buy? And where is the best place to buy it?
Any help would be appreciated.
Thanks

 

[Twainer]

I used "Great Stuff" spray foam from box store. I looked it up & they state that it is a closed cell foam. I filled the whole cavity except areas where water needs to drain. I put in more than the factory had cause it will not only help with floatation but deaden sound as well. Just as I stated before make sure you do not block any areas that are dedicated for water flow should a leak ever happen.

 

[Frey0357]

Hello 72. I used 4 sheets of 1" thick "pink" foam that I got from one of the big box stores for my 16.5' Sea Nymph. I cut to fit each piece and while that was time consuming it fits real nice and is very solid under the wooden flooring. Huge improvement over the old water logged spray in foam stuff. Just my opinion here tho!

Frey

 

[Kern Fischer]

The amount you choose to use will depend upon how much flotation you desire. The boat I am restoring/rebuilding/updating is getting so much attention that I never want it to sink. Every cubic foot of flotation provides about 60 pounds of flotation capability. I am using the pink foam sheets and bonding them in place wherever possible to gain volume. Each of these sheets is about 2 2/3 cubic feet of volume and provides about 160 pounds of flotation. If you do not want the boat to sink, you need enough flotation volume to equal the total weight of the boat and motor. The volumes need to be concentrated as much as possible in the areas where the heaviest weight is located.

I will have flotation located from bow to stern but will be filling the stern areas as much as possible to support the motor and battery..

For my bottom structure, I will be filling the entire cavity with foam. The cavity will be totally sealed and will not allow any possible water entry. This will aid the stiffness of the hull and prevent water from reaching any of the wood structure. If I should hole the hull for any reason, water will not fill the boat and a repair can be easily made.

 

[tpenfield]

For boats you want to use the 2-part pour-in urethane foam. the great stuff would not be a good solution and is far more expensive than the pour-in.

You will need to figure the volume of the chambers under the floor and then go about 10% more to be sure. As mentioned, you will also want to compare the volume of foam and the weight of the boat/engine. Typically you do not need 100% of the weight of the boat for what is known as positive flotation. If the volume under the floor is inadequate though, it would be good to know, so you can put additional flotation elsewhere in the boat.

Also, the foam adds a lot of strength to the boat itself, so long as you use the our-in kind of foam.

Usually flotation foam of the pour-in style gives a 30:1 expansion, when used at a temperature of 80 F. A cubic foot is = to 7.48 gallons. So, a 2 gallon foam 'kit' will yield about 8 cubic feet of foam or about 480 lbs. of buoyancy.

Best to take some measurements of the chambers that are under the decking of the boat and if you know the weight of the boat/engine, that will be useful too.

 

[mickyryan]

when I did mine I came up with 9 cubic inches per oz , seemed to work for me after doing the math to figure out volume of cells

 

[72cheyenne]

Thanks everyone for the answers. It really helps me out. I think I will go with the 2 part pour in foam. I have heard of the pink foam board and pool floating. But I do feel the pour in will add some strength. Thanks again

 

[lkroneschm]

I used "Great Stuff" spray foam from box store. I looked it up & they state that it is a closed cell foam. I filled the whole cavity except areas where water needs to drain. I put in more than the factory had cause it will not only help with floatation but deaden sound as well. Just as I stated before make sure you do not block any areas that are dedicated for water flow should a leak ever happen.

How did you separate those "drainage" areas from filling with the pour in foam? I am restoring a 1958 Texas Maid aluminum boat with drainage baffles all along the floor . I want to put the foam in the floor cavities but there are drainage gaps in each cavity.