Re: Expanding (pour in) Flotation Foam and Aluminum Boats
I just want to address a few of the comments here. The answers are based on my experience testing boats for flotation over about 20 years or so, and helping manufacturers comply with the flotation regs.
Some one asked why manufacturers use pour foam: It's cheap and simple. It is easier to make a compartment, drill a hole in the top, and shoot spray foam in for a Known number of seconds, than it is to cut up board foam, fit pieces in and then attach a cover. The second takes more time and several more bodies to do than one man or woman with a foam gun.
It was asked why does some foam absorb and some not. As I said in my previous post, I believe there are a number of reasons. All foam used in boats is supposed to be closed cell foam. Closed cell foam does not absorb water. So what is happening? for some reason some of the cells are NOT closed. This can be do to improper installation, or it can be due to incorrect chemical composition. The problem has gotten worse since the manufacturers changed the blowing agents in 1995. Water absorption can also be due to simple age. I don't necessarily mean chronological age. The foam in a boat that is heavily used will age faster than in a boat that is infrequently used. That also depends on how the boat is stored. If water is allowed to stand in the boat for long periods with freeze thaw cycles, it will age faster. Shock, vibration, and stress will all affect the foam and cause it to age. But it should last far longer than it does in some boats (not all by any means)
Also the law is not seven years. Recreational boats are required by US law (Canada too) to be in compliance for ten years from the date the boat was entered into interstate commerce (which can be different than the date it was made) But boats made before 2000 were required to be in compliance on five years, and the ten years was phased in over five years, so in 2003 it would have been seven years.
Most aluminum boats made in this country are small utility type boats. Most of those use plain old styrofoam in sealed boxes. They don't have this problem. Some larger aluminum boats use pour foam. They do have this problem. But it has nothing to do with the hull material.
How is the amount calculated. It's not rocket science doesn't take an engineer. I taught this stuff to boat builders for many years. You can see how to do it here (my page)
http://newboatbuilders.com/pages/flot.html
Here (the US Coast Guard's handbook)
http://www.uscgboating.org/regulations/boatbuilder_s_handbook/flotation_landing.aspx
Or here: The Safety Standards For Backyard Boatbuilders (no longer published by the USCG)
http://newboatbuilders.com/docs/backyardboatbuilders.pdf
It is based on three things, weight of the boat hull (and machinery for inboards), weight of the persons, and weight of the engine for outboards. All the calculations assume you are using 2 lb density foam, that is one cubic foot weighs 2 pounds and will support 60.4 lb in fresh water and 62.4 in salt water.
Do pool noodles support the same as other foam. Yes if they are two pound density foam. One cubic foot of pool noodles will support the same amount as an cubic foot of two pound density foam. Many years ago I did the calculation for 6 foot, 3 inch diameter pool noodles, but I can't seem to find it. But anyone who knows how to calculate the volume of a circular object can do it.
Placement of the foam in the boat is just as important as how much. Putting too much in can cause problems as well. We even failed a Boston Whaler because it had too much foam placed too high and the boats simply rolled over. Yeah it would float, upside down. That's not the point. Outboards are supposed to float upright, so that a person in the boat would have the upper part of their body out of the water. This helps prevent hypothermia. The exception is inboards (I/O's included) which just have to float with some part of the boat out of the water.
Anyway, great discussion. Great learning tool. Don't stop now!
