flotation foam

[bennyfamily]

i have a 75 mac venture. the po has removed the flotation foam in the aft of the boat. my ? is how much foam should be there and were was it. a pic would be nice. also can i use flotation air bags instead.

john

[Bob McLellan]

As long as you are on the subject, I have asked this questions many times - not how much was originally in the boat - but with all the weight we add with the motor, gas, gear, etc; will the flotation really work? I hear of people taking out some for really neat lockers in the bow. Is there a calculation for cubic feet of foam vs weight? Personally, I would rather have it - makes you feel secure anyway

[Bob McLellan]

On my 1976 V-25 there are three foam blocks 12x12x36" each, providing 9-cubic feet of flotation. They are located in the center of the rear lazarette under the cockpit floor and behind the battery. They wedge in tightly in my boat. To gain storage space, I have seen folks break up the foam and stuff it between the liner and hull on the port and starboard sides. If I did that, I think I would use some Styrofoam I saw at West Marine and foam in place. Has any one tried that? The Home Depot foam in a can will absorb water - not good!

[johnnyonspot]

As far as how much you need, it should be a simple computation of the weight of the water displaced by the foam and the boat/equipment vs. the weight of the boat. Or a simpler method would be to add up the weight of the added equipment and ensure enough foam is added to displace an equal or near equal amount of water. This assume there was enough foam to begin with to float the boat with the original displacement amount.

[Bob McLellan]

So, I guess the real question is: how much weight will one cubic foot of foam support?

Is it true that "if" one cubic foot of foam displaced one gallon of water, and one gallon of water weighed 8-pounds - therefore one cubic foot of foam will hold up 8-pounds?

[Bob McLellan]

Sorry - forgot to answer the question about air bags: I would not use air bags just from the reliability standpoint. I remember just off Redondo Beach CA that they raised a sunken boat using ping pong balls. I guess the slow accumulation of the blown in balls finally did it.

You can use styrofoam that is as house insulation and is sold at Home Depot. It cuts real well on a band saw using a 14 tooth blade - no mess. You can use a glue such as Titebond to glue the cut pieces together into a larger block. Here in Arizona you can get it in 2-inch thick sheets 2x8-feet

[Don T]

Hello,
AND, stuff doesn't weigh as much submerged (specific gravity). GRF for example is around 1.05 SG so it doesn't weigh much when you are sinking. A lot of your personal effects have a low SG too. Things like engines, batteries, ballast and such are the main sinkers.

[johnnyonspot]

So, I guess the real question is: how much weight will one cubic foot of foam support?

Is it true that "if" one cubic foot of foam displaced one gallon of water, and one gallon of water weighed 8-pounds - therefore one cubic foot of foam will hold up 8-pounds?

Get a bucket large enough to accomodate the foam, fill it to the brin with water (seawater if in the ocean and wanna be really anal about it), and set it inside a larger container that can catch the water that goes over the edge when you push the foam block down into the first bucket of water. The mass of the water that escapes should be the mass that the foam will float. Or perhaps I am really confused.

[dennisneal]

I believe I can contibute something:

A cubic foot of saltwater weighs about 63 pounds.

A cubic foot of styrofoam weighs about 0.6 pounds, let's say 1 pound.

It seems to me that an additional cubic foot of styrofoam should float about 60 pounds of additional boat weight, provided that the structure of the hull/deck does not rupture under the stresses. On the other hand, the removal of a cubic foot of styrofoam would mean the boat would be able to keep afloat only if it weighed about 60 pounds less than the designed maximum.

As mentioned earlier, an episode of "Mythbusters" on the Discovery Channel, actually showed how to refloat a sunken boat by injecting ping pong balls into the cabin/hull.

In general, I am not an engineer, but I cannot recommend removal of any styrofoam from the hull.

Happy Sailing,

[bennyfamily]

the po removed the foam not me . i want to know how much to put back.a lot of good info. any one used the two part foam mixe. can i use it?

[Bawgy]

My venture 24 has big blocks of foam from the bilge to the bottom of the cockpit floor and blocks stuffed into the v-berth bilge area

[Retcoastie]

You might want to check your insurance policy. Removing manufacturer installed positive floation voids some policies.

[Phillip]

Another idea for cutting foam.
We once used a stryro display box with interior styro support trays.
Had hunders of them we had to cut down over the years.
We used a hot wire (old elec heater wire) in a made up frame and powered it with a 12V battery.
Nice clean cut.
Wear a mask....smoke/fumes are dangerous.
Finished product is good tho.
You can cut neat curves...anything.
Make sure you use the good stuff, not the really soft crumbling stuff you often find in electronic packing.


(Oh...another point, different foams have different density's.
An aquantance has a busines ,re-cylcle foam styro, to China. he compress's it 40-1 and it comes out in 4'x4'x4' block...(fits container perfectly, 2 blocks wide, 2high etc. Guess what it comes back to us as.....expensive clocks, expensive really fancy picture frames etc. It is as solid as timber....sorry....should stick to the topic)

Cheers
Phillip