How much foam do I need in my boat?

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jester49
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Joined: 25 Jul 2018, 22:47

How much foam do I need in my boat?

Post by jester49 » 18 Sep 2018, 22:18

I have a 16" Starcraft deep/wide. Wondering how much foam I need for buoyancy? Also where to put it and what type.


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Xtremeboats
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How much foam do I need in my boat?

Post by surfman » 19 Sep 2018, 07:04

Bouncy is equal to the amount of water displaced, If the boat weighs 200 lbs and you want it to float then you need to displace 200+ pounds of water. Where to put it? Where ever you can.

uttexas
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How much foam do I need in my boat?

Post by uttexas » 19 Sep 2018, 08:36

I would use closed cell foam

The double sided insulation foam board is commonly used
Pool noodles (which are about to go on clearance everywhere) are also popular
Closed cell foam flooring squares and exercise/yoga mats also work.

In general, I'd avoid the spray can foam and the two part expanding foam--over time, they can get water logged. If you over do it, can cause some structural stress.

jester49
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How much foam do I need in my boat?

Post by jester49 » 19 Sep 2018, 11:01

Pool noodles will work??

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gillhunter
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How much foam do I need in my boat?

Post by gillhunter » 19 Sep 2018, 11:28

Check out the sticky on foam right above your post.

jester49
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How much foam do I need in my boat?

Post by jester49 » 19 Sep 2018, 12:41

gillhunter wrote:Check out the sticky on foam right above your post.
What am I looking for lol

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BigTerp
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How much foam do I need in my boat?

Post by BigTerp » 19 Sep 2018, 13:54

jester49 wrote:
gillhunter wrote:Check out the sticky on foam right above your post.
What am I looking for lol

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onthewater102
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How much foam do I need in my boat?

Post by onthewater102 » 19 Sep 2018, 15:35

The 2 part expanding urethane is my choice - it doesn't react to gasoline should any spill (insulation boards will dissolve into goo and their type of foam isn't allowed in the lower portions of the hull per federal guidelines.) It does complicate things a bit though - too much foam poured into too small a volume will exert a significant amount of pressure as it forms, and if not properly contained/confined it will fill a cavity completely creating drainage issues through the area.

No foam is 100% closed cell, so any of them will take on water over time if left submerged. The closed cell expanding foam tends to do a better job of trapping water around itself and therefore gets a bad rep for becoming water logged when the material itself isn't to blame - it's poor preparation of the area and poor design.
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Tinny Fleet
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How much foam do I need in my boat?

Post by Tinny Fleet » 20 Sep 2018, 09:13

Well, pool noodles were on closeout at my local Wal Mart a couple weeks ago for 52 cents a noodle. Using finger digit quantum physics, with respect to my 16' starcraft, and err... hull curvature and all that, I calculated 25 noodles, but bought 30 anyway out of an abundance of caution. So with luck, I'll be able to get the job done for $15 bucks, and still have a spare noodle or two to pad a cartopper rack for the top of my van!
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onthewater102
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How much foam do I need in my boat?

Post by onthewater102 » 20 Sep 2018, 09:30

They're at least polyethylene foam so they won't react if gas spills on them. You just won't get any hull support from them, they'll certainly help float in an emergency. If they're 3" in diameter with a 3/4" cutout in the center and 5' long they'll displace a little less than a quarter of a cubic foot of water each. They're very low density, so probably 60 lbs of flotation per cubic foot would be a safe assumption. So you're looking at a little less than 60lbs of flotation for every 4 you add to your boat.

28 would be able to support about 400lbs of dead weight in the event your boat goes down. Just need to install them relatively evenly around in the boat and concentrate them only in areas that bear a lot of weight (near your battery compartment and transom for instance.)
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Tinny Fleet
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How much foam do I need in my boat?

Post by Tinny Fleet » 20 Sep 2018, 10:02

Realization: 28 noodles=only 400 lbs flotation? A person would need twice that, or more, to keep a 15' Starcraft afloat. 430 lbs for hull, 120 lbs for motor, and, say 300 lbs for battery, trolling motor, gas tank, seats, tackle boxes, misc. important stuff. One wave and its Davey Jones' locker! Yikes!

Is there something else that a person could use that has a higher "floatability"?
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onthewater102
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How much foam do I need in my boat?

Post by onthewater102 » 20 Sep 2018, 10:04

Not really. A cubic foot of water weighs a smidge over 62lbs. At only 2lbs/cuft foam is one of the lightest options out there - you're not going to gain anything meaningful with a different material.

Check out my thread on my tracker III linked in my signature - I just poured foam in between my floor ribs last night, each cavity is 4' wide, ~14" wide and 1.5" deep. I added roughly 3 cu.ft. of flotation just by filling these cavities beneath my floor. On a 15' boat you probably have a similar space to work in - you might be surprised how much wasted space there is that you can put to use for safety in the event of an emergency.
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Ebug
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How much foam do I need in my boat?

Post by Ebug » 20 Sep 2018, 10:30

I recently watched a boat builder place an Industrial strength trash bag from a big box store into the cavity he was going to pour expanding foam into. The foam was poured in and the bag folded closed.

This was on a wooden racing hydroplane boat. The builder said this allowed him to rebuild the foam portions of the boat without having to chisel foam off all the panels.

I guess a second benefit is it adds a barrier to prevent water from saturating the foam.

Rob

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onthewater102
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How much foam do I need in my boat?

Post by onthewater102 » 20 Sep 2018, 10:49

I did something similar with painter's plastic over larger areas than a bag would have fit for all the same reasons.
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water bouy
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How much foam do I need in my boat?

Post by water bouy » 20 Sep 2018, 16:35

Somewhere I read that noodles would eventually absorb water so I went with the sheet type. If the boat has or had benches you could calculate the volume of them since they would have contained foam. Pics would help.
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