How much 2" polysterene?

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aeviaanah

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I just bought a 2" x 4' x 8' sheet of polystyrene. Not sure how much buoyancy to a cubic inch or ft. I have a 12' aluminum mod V. Should weight in around 600-800lbs when finished.
 
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aeviaanah

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Re: How much 2" polystyrene?

Re: How much 2" polystyrene?

Nominal density (pcf) is 1.0
 
oops!

oops!

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Re: How much 2" polystyrene?

Re: How much 2" polystyrene?

hi ....welcome to iboats.

the sticky at the top of the restoration forum ....has uscg rules........these include foam calculations
 
tpenfield

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Re: How much 2" polysterene?

aeviaanah said:
I just bought a 2" x 4' x 8' sheet of polystyrene. Not sure how much buoyancy to a cubic inch or ft. I have a 12' aluminum mod V. Should weight in around 600-800lbs when finished.
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Figure that you will get 60 lbs of buoyancy per cubic foot of foam.

4 x 8 x (2/12) = 5.333 cubic feet. So it will give about . . . 60 lbs/cu. ft x 5.333 cu ft = 320 lbs buoyancy for each sheet.
 
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aeviaanah

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Re: How much 2" polysterene?

oops! said:
hi ....welcome to iboats.

the sticky at the top of the restoration forum ....has uscg rules........these include foam calculations
Click to expand...
I downloaded the boat builders handbook....Im not all that good at math but ill try to figure it out.
tpenfield said:
Figure that you will get 60 lbs of buoyancy per cubic foot of foam.

4 x 8 x (2/12) = 5.333 cubic feet. So it will give about . . . 60 lbs/cu. ft x 5.333 cu ft = 320 lbs buoyancy for each sheet.
Click to expand...
Ok will do. thanks man...so if my boat weighs 600lbs with everything on it, i need two of these sheets??
 
Yacht Dr.

Yacht Dr.

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Re: How much 2" polysterene?

12 footer ? .. I would suggest some PFD's ..

Have any pics to post up please :) .

YD.
 
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aeviaanah

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Yacht Dr.

Yacht Dr.

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Re: How much 2" polysterene?

PDF = Personal Floatation Device .. commonly known as a life jacket ;) ..

Do you actually think that there may be a situation that you could swamp the boat and need floatation foam ?

Just wondering ..

YD.
 
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fishrdan

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Re: How much 2" polysterene?

You need to keep the boat floating in the water, not above the water. A 600# boat will not require 600#'s of flotation to keep it from sinking since aluminum is not as heavy in water, as it is in air. A cuft of aluminum is 165# while a cuft of water is 62#, so you only need 104# of flotation to keep the cuft of aluminum at the water's surface. There are also things that float or are neutrally buoyant, wood, fuel tank, etc.

I'm not sure how much flotation you will need, but I doubt it's 600# worth. Either way, I would error on the side of safety and put in a bit more than needed.
 
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aeviaanah

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Re: How much 2" polysterene?

Yacht Dr. said:
PDF = Personal Floatation Device .. commonly known as a life jacket ;) ..

Do you actually think that there may be a situation that you could swamp the boat and need floatation foam ?

Just wondering ..

YD.
Click to expand...
Both my gal and I have life jackets Thanks!
fishrdan said:
You need to keep the boat floating in the water, not above the water. A 600# boat will not require 600#'s of flotation to keep it from sinking since aluminum is not as heavy in water, as it is in air. A cuft of aluminum is 165# while a cuft of water is 62#, so you only need 104# of flotation to keep the cuft of aluminum at the water's surface. There are also things that float or are neutrally buoyant, wood, fuel tank, etc.

I'm not sure how much flotation you will need, but I doubt it's 600# worth. Either way, I would error on the side of safety and put in a bit more than needed.
Click to expand...
I did factor in how much things weigh under water. I used .6 or so for aluminum.
 
tpenfield

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Re: How much 2" polysterene?

aeviaanah said:
Yea 12 foot. What are PFD's? Here are a few pictures.

View attachment 117797View attachment 117798View attachment 117799

I did the math from the boat builders hand book. seems ill be needing two of these sheets, thats ridiculous. I cant fit all that foam in this small boat. It will be used on rivers and lakes with a bilge pump. Any ideas?
Click to expand...

Just remember, if you build a boat and it sinks, you get no partial credit.

Actually, putting 600 lbs of flotation on a 600 lb boat will have it floating high in the water. If you want to have the boat merely at the surface, you could figure the boat's buoyancy into it, requiring less foam.

If you figure that the boat's material is 4 times as heavy as water, then 600lbs of boat will yield 150 lbs of flotation. So, instead of needing 600 lbs of flotation from the foam, you will only need 450 lbs. that is 1-1/2 sheets instead of 2 sheets.

You may still have to get creative as to where to put it all.

I added 32 cubic feet of foam to a Catalina 22 foot sailboat (equivalent to 6 sheet of the 2" foam boards). It took a while to find places for it, but in the end, 32 cubic feet it was.
 
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aeviaanah

Petty Officer 3rd Class
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Oct 4, 2011
Messages
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Re: How much 2" polysterene?

tpenfield said:
Just remember, if you build a boat and it sinks, you get no partial credit.

Actually, putting 600 lbs of flotation on a 600 lb boat will have it floating high in the water. If you want to have the boat merely at the surface, you could figure the boat's buoyancy into it, requiring less foam.

If you figure that the boat's material is 4 times as heavy as water, then 600lbs of boat will yield 150 lbs of flotation. So, instead of needing 600 lbs of flotation from the foam, you will only need 450 lbs. that is 1-1/2 sheets instead of 2 sheets.

You may still have to get creative as to where to put it all.

I added 32 cubic feet of foam to a Catalina 22 foot sailboat (equivalent to 6 sheet of the 2" foam boards). It took a while to find places for it, but in the end, 32 cubic feet it was.
Click to expand...
Yea you are right. I think I am just going to get foam wherever I can. I was probably going to do that anyway. Its still good to know how safe the boat is :) NO CHILDREN ON BOARD.
 
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