foam under deck

[lstewart0912]

Do i need to replace the foam under my floor when replaceing the floor and if so how much do i need to put back ot is a beretta 19 foot inborad fiberglass boat very new to all this tips would be appreciated thanks so much

 

[jbcurt00]

Yes, calculated by volume of area you need to fill.

2lb expanding foam is sold in by the cubic foot units.

 

[lstewart0912]

So how much do i buy so sorry very inexperienced at this and where can i buy it and should i used open cell or closed cell

 

[woodstockmarine]

I would leave it. just put the new floor over the old foam.

 

[MTboatguy]

If the foam is wet, you don't want to leave it, it adds a lot of weight to the boat, and if you are replacing the floor, your foam is wet, which will again cause problems in the future, you don't want to do all this work and then have to do it over in a couple of years. Also the stringer need to be checked and repaired as problems are found, and you need to check the transom, cause if the water got in to damage the floor and the stringers, you can bet it got into the transom and is going to cause problems.

Once wet, that foam will never dry, it becomes a liability and won't do what it is suppose to do in the event there is a breach in the hull. Once you get everything re-done, foam is actually quite easy to do, and don't think you can do it with expanding insulation foam, don't work so good, not dense enough and will breakdown after a while.

Do it right the first time and you should not have to do it again. In order to figure how much to buy, you need to calculated the cubic volume under the floor. Just do a search for Boat Flotation Foam and you will find lots of places selling it and I am sure there are many here that will give you recommendations as to where to get it.

 

[jbcurt00]

Why are you replacing the deck in your boat?

What else, besides new foam, needs to be done before you're deck goes back in?

 

[gm280]

To calculate cubic volume, you have to measure the area under the floor. And you can do that in a couple different ways. Either do it all in inches, or all in feet. If you have 6 inches under the floor to the hull and the area is 5' wide and 10' long the you can convert those dimensions into inches to work it out. So 6" X (5' X12") X (10' X 12") would be that method. AND that would be 6" x 60" x 120" or 43200 cubic inches total. And every cubic foot has 1728 cubic inches in it. So divide your answqer by 1728 to get the total number of cubic feet you will need to purchase. And in this example that would be 25 cubic feet. Or you could equally do the same calculations in feet. Then you would have .5' X 5' X 10' or again 25 cubic feet. So however you want to do it. Just remember that it is height X wide X length and you will arrive at cubic feet however you want to do it. Then buy the proper amount of mix and pour foam and you're good!

 

[jigngrub]

An easier way to do it is to look at the Coast Guard capacities plate for your boat and find the maximum weight for your boat and divide by 60, this will give you the number of cubic feet of foam needed to float your boat.

For instance:
If the max capacity for your boat is 1380 lbs, divide 1380 by 60 = 23. That means you need 23 cubic feet of floatation to float your boat.

 

[DeepBlue2010]

Hi,

As was stated by others, you sure don't want to leave wet foam there. It is a dead weight that will heart your fuel economy and will serve no purpose in keeping your boat afloat if the boat started to take water. The moisture also will find its way - sooner or later - to your new wood and ruin it. So, as you see, it is a bad deal all around.

The type of floatation foam you need to use is closed cell. This means, it will not absorb water if submerged but will rather disperse the water and keep your boat afloat.

The calculations above is - of course - correct mathematically. The volume of a cube of length, width and height a is a*a*a or a^3 all measured in the same units. And the volume of a rectangular prism of dimensions a,b,c = a*b*c all measured in the same units. Conversion factors can be used to convert between units.

However, depends on the shape of your hull, your calculations might not be that simple and require some math work to calculate. If the shape is not that easy to calculate the volume for mathematically, one practical way to give you the first approximation or initial estimate is to fill the spaces that will be foamed with water and measure the water when you pour it in. For example, if the space is small you can use fluid ounces to fill it or if it big you can use gallons etc. Of course, I would do my best to do this after taking the old wet foam out and before I start my new build. At the end, convert all of these measures to cubic foot and you will know how much you need in total but more importantly you will know how much you need to mix to fill the entire volume of each cavity with its maximum capacity.


Some other builders just mix whatever quantity and drill two holes (fill and overflow) and start pouring in until the foam comes from the overflow hole. So many ways to skin this cat. Best of luck to you

 

[Watermann]

Some great advice offered above and here's all I have to add. Buy a good cover for your boat and use it.

 

[woodstockmarine]

This stuff is not like styrofoam. High density foam does not soak up water like a sponge. Take a core sample I mean dig a little hole and you will see the moisture does not permeate more then a 1/4 inch or so. Unless it is overly moldy I would still leave it in.

 

[Grub54891]

This stuff is not like styrofoam. High density foam does not soak up water like a sponge. Take a core sample I mean dig a little hole and you will see the moisture does not permeate more then a 1/4 inch or so. Unless it is overly moldy I would still leave it in.

Check down low with a core sample,mine was dry the top inch or so. Sopping wet the deeper I went. Removed it all,about 200 saturated pounds. Replaced with 2lb foam. Lighter boat means more speed!

 

[jbcurt00]

This stuff is not like styrofoam. High density foam does not soak up water like a sponge. Take a core sample I mean dig a little hole and you will see the moisture does not permeate more then a 1/4 inch or so. Unless it is overly moldy I would still leave it in.

this not the case w the vast majority of the boats w rotten decks, tin or fiberglass, that get posted

take a 2" pvc pipe and cut teeth around one end to make a coring tool.

Drill a hole thru the foam all the way to the hull.

Remove the foam in your core hole all the way to the hull.

If there is no water in the bottom of the hole, wait a bit and check again
.

No matter what the result is for that 1 core hole, thats 2" out of hundreds of square inches of foam and hull interface.

read thru some other resto topics, its fairly easy to see which is more prevalent, minimal water intrusion or major.

 

[MTboatguy]

This stuff is not like styrofoam. High density foam does not soak up water like a sponge. Take a core sample I mean dig a little hole and you will see the moisture does not permeate more then a 1/4 inch or so. Unless it is overly moldy I would still leave it in.

I have tore a lot of boats apart over the last 30 years and virtually all of them had water logged foam, it might not penetrate easy, but once it does, then it is wet forever, if it has got to the point the floor needs to be replace, you can rest assured the foam needs to be replaced as well, it might feel dry to the touch on the surface, but it is wet inside, like I say, I have tore a lot of them apart over the years and most of them had water logged foam.