How do flooded boats float, foam , air spaces ?

[Coyotes-R-Us]

Water weighs about 62 pounds per cubic foot or about 7.5 gallons per cubic foot..... one gallon is 231 cubic inches...
Weigh your boat and do the math for the amount of flotation required to keep it from sinking to the bottom...

With that and what I plan to use foam=39744 qb" of foam=172 gal water=1421 pounds ????
With about half that would hit the water first before the cats filled with water . HUMM
What do you think ? plenty?

[Bart]

here are a couple of links, that might help out
from looking at the specs on the second link they have this, measurement to go by. a 10" x 20" x 9' will float 665lbs. or one cubic foot of EPS will float 60lbs of weight. I remember working down at the city docks one summer, replacing the floating docks. there was a couple of the foam logs that we had to place under a couple of the docks. one of them shot out about 30 feet. before we could get it secured to the float.
both of the links even encapsulate the foam in a liner similar to you plastic on a gas tank. and does custom sizes. something like that would work between the cats.
looks like you are having to much fun.
http://www.geofoamamerica.com/products/flotation-foam-logs/
https://univfoam.com/products

[Coyotes-R-Us]

I'm going to use "Pink" foam boards cut to fight , rapped in nylon water proof fabric like a pillow case closed with Velcro.

[Corky]

Here's the other part of the equation you haven't thought about...Buoyancy center of gravity...I know this the hard way...I have foam under each seat in my small red mini jon..{foam under the front "step",middle seat and rear seat under the engine}...If it fills up with water the bow will float but the weight of the engine,prop and cage will weigh the rear down and it sets on the bottom...Now, the foam is almost enough to float the rear and if you wade out and lightly pull up on the cage it will come right off the bottom...

Here's the catch : The engine and cage has such a high center of gravity the foam tries to roll the hull !!!..Much like trying to hold a beach ball under water...With the hull completely full of water there's nothing to stop the boat from simply rolling on it's side and just keep going until it's completely upside down...Which ever side you stand to steady the boat it's guaranteed to try and roll out the other side...I always have to pull the boat to shore as far as it will come{to keep the bow steady} and start bailing with the gunnel right at the water line...It's a pain for sure and probably the reason you don't see the foam used much in an airboat..
You on the other hand would have an advantage because the pontoons would make for a nice,wide footprint under the engine,cage,and prop..But foam placement is going to be tricky you can't just add it where it's convenient it almost needs to be designed with flotation in mind to make it work properly...

[Coyotes-R-Us]

HUMM , Interesting . Let me think on that.
I'll try to get a diagram and put it up.