Foam, flotation and all that

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BaitCaster

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Just got my boat back from the Tracker dealer (brought it in to fix a leak in the live well). Technician noticed the deck hatch I installed in the bow and commented that I had "cmopromised" the flotation and that removing even a little foam can make a big difference. Well, I am now installing another deck hatch in the rear bench seat (pics to follow on my "Livin Large" thread) and will be removng a good sized chunk of foam and I'm getting paranoid about the flotation.

I was thinking about glueing some foam panels between the ribs on the floor and then laying my rubber tile flooring on top. So, the questions are:

1. What type of foam do I use?
2. How do I adhere the foam to the hull of the boat?
3. Is it okay to have the foam exposed to the elements (i.e., under my rubber mats) or would I be better off putting a sheet of plywood on top. I would rather avod adding the weight of the plywood. Is there a way you can paint "treat" styrofoam sheets?

Any advice is appreciated.

Cheers,
BC
 
Ugh, do a search for ideas. Here's the condensed CG boatbuilders guide version. Closed cell floatation must be fuel resistant within 4" of the bottom of the hull and should be installed in the upper sections of the hull to keep the boat upright in a swamping event. Open cell (styrofoam) will absorb water and fuel will cause it to break down. I'm using 1" closed cell sheet insulation from Lowes under my decking with cross bracing 4" off the floor to hold the insulation out of the bilge. I did put some under the center section floor, more to support the floor and dampen noise.

What I would suggest is make sure the rear section foam is left intact or add more to support your engine weight. The CG regs say the boat must float level when full. Add some floatation in the rear corners or in out of the way areas to make up for what you removed. I added pods so I could extend the rear deck and they sill be filled with foam (hopefully todat).

Do a google search for coast guard boat builders guide and read up on it.

Jamie
 
So, I'm no expert, but here's what I think. You should glue it to the boat if for no other reason than the squeaking of foam as it rubs against any other thing is maddening. I used foam glue in tubes that was applied with a caulking gun and weighted it to be sure it was good and stuck. I would cover it with a floor of some kind whether it is plywood, aluminum or Sintra. The foam will dent and crush eventually and you'll have pieces breaking off and an uneven floor. It needs to be covered also to prevent degradation by the sun and elements. Most types of foam degrade from the weather and the surface becomes powdery, not the kind of stuff you want in your eyes or lungs as you're moving along at speed. If you're worried about weight start looking for aluminum road signs. The aluminum is pretty easy to machine with common shop tools and will make a really good, permanent floor.

At the risk of starting a debate, I will avoid the question of which foam to use. Closed cell, open cell, pink, blue, yellow, foam-in-place and so on. I used pink closed cell and as I haven't tried to sink the boat yet can't report on whether it works or not.
 
Your technician is right, removing even a little foam can be bad; if the foam was marginal to begin with. Let' say you removed 4 cubic feet of foam, 2 cubic feet in the front and 2 cubic feet in the back. Each cubic foot of foam provides 60 pounds of buoyancy, so you have reduced the buoyancy potential of the hull by 240 pounds. If the foam was spot on for gross weight then reducing it by 240 pounds may be enough to cause it to sink tot he bottom. 2 cubic feet isn't much either, a 20 x 14 x 12 hole is almost 2 cubic feet (1.94 to be exact).

The only way to know for sure is to know what gross weight of the boat is, how much foam is in there now and whether or not removing some of it would cause you to go below the magic number.

Here is a quick example: If your gross weight is 480 pounds (hull, motor, gear and people) you will need 8 cubic feet of foam to provide upright and level flotation. If you then removed 4 cubic feet you would only have 240 pounds of flotation left which would mean your boat sinks.

I always recommend that we install USCG approved foam; and the main reason is that in the event you sell the boat, if something other than USCG approved foam were used, you could be held liable for damages. I am not saying that pink sheet foam will not work, but it has not been tested for fuel degradation or water absorption like approved foams have.
 
Keep all the foam that you take out of your boat and cut it to fit somewhere else. This way you know that is approved by the USCG and reduces your liability. Just make sure it's evenly distributed, raised off the bottom of the boat and put all of it back in your boat. If you have ever tried to cut Styrofoam with a saw you know it's going to chunk and break apart. I had a custom surfboard made a while back and I watched the shaper cut large foam blocks down to blanks. He bought foam in bulk and used a hot foam cutter that cut it like butter. I just found the site below that shows how to build one. I'm thinking I should still keep a fire extinguisher handy and not cut it in the garage. I'll let you know if it works.
https://www.hhhh.org/~joeboy/resources/hotwire_foam_cutter/hotwire_foam_cutter.html
 
Most jon boats will float even when completely filled with water (completely swamped) because of the foam. Since you removed some foam there is no telling if the boat will float when swamped.
 
I don't know if you found your answer or not. The measurements given by Rat sounded pretty solid. I was looking for products that were approved by the CG and came across this:

https://www.jgreer.com/boat-foam.htm?gclid=CLWn0Zjfw6QCFZNg2god0ClcDg

It's a two part CG approved foam. You could mix it and apply it where needed. I've used this sort of thing before and it can get messy and will probably not adhere to the sides thus settling to the bottom. The good news is it expands to fill every void you pour it in. If needed you could make a form, pour it and wait for it to cure and then cut it up as needed I would think. Just a thought.
 

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