Flotation foam

Designs for inboard or outboard power

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weller
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Flotation foam

Post by weller » Sat Jun 22, 2019 7:55 am

I'm building the Atlantic skiff and was trying to decide if I should use flotation foam. It seems like all the ways to figure out how much I need require a masters degree in mathematics. Can anyone help me out here and figure if its even plausible for me to fit enough foam inside to make it float.
"My mind is on a permanent vacation, the ocean is my only medication"

JimmY
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Re: Flotation foam

Post by JimmY » Sat Jun 22, 2019 9:20 am

One cubic foot of water weighs about 62 lbs. Say a cubic foot of foam weighs a few lbs, so estimate about 60lbs of flotation for every cubic foot of foam. If your boat is wood, the wood will be naturally buoyant. So, the flotation just needs to float the non-wood stuff on the boat (e.g., motor, battery, hardware, etc...). Add up the weight of all that stuff and divide by 60 and that will be the number of cubic feet of foam. These are rough estimates and it should keep a swamped boat afloat.

I used plastic, collapsible water jugs and just tucked them in wherever they would fit. They come out easily if I have get at something and don't trap moisture like foam.
-Jim
Nothing says poor craftsmanship like wrinkles in your duct tape!

TomB
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Re: Flotation foam

Post by TomB » Sat Jun 22, 2019 9:41 am

Your build in the Gallery? Nice job.

I'm working through this on my build too.

How much do I need?

Add up the stuff that sinks, plus a bit, that's the minimum I need.

How many cubic feet of flotation do I need?

Water weighs 62 lbs/ cubic foot. Flotation foam goes at about 2 lbs/ cubic foot. So I get about 60 lbs of water displacement (buoyancy) for ever cubic foot of foam.

How much I need divided by 60 = Cubic feet of foam needed.

What are the foam choices?

GlenL sells a two-part foam making 5 cubic feet. -- Cubic feet needed/5 = number of cans needed

or Polyethylene planks come in multiple thicknesses and widths by 9' long. www.foamforyou.com is a source I have used. I am looking at 2"x24"x108" which yields 3 cubic feet so it tucks between frames. Cubic feet needed/3= number of planks needed

Plausible?

I need about 20 cubic feet of foam or 7 planks or 63 linear feet of foam. I have 8 frame spaces to stick foam in, so I need about 8' feet per space, average. Plausible, if I fill it up. Your results may vary.

Good luck,

Tom

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Bill Edmundson
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Re: Flotation foam

Post by Bill Edmundson » Sat Jun 22, 2019 10:04 am

Weller

You need closed cell poly urethane. I like the blocks that I can get from and upholstery supply shop. It may cost a little more. It is easy to cut. I have used the foam in place stuff. It is messy and difficult to work with.

The blocks I try to use are 2"x24"x107". I think that is about 178# of floatation.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
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weller
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Re: Flotation foam

Post by weller » Sun Jun 23, 2019 3:31 am

Thanks guys. I understand that the weight of everything that does float I need foam for. I didn't weigh anything I put in like the engine, transmission, shaft, prop, gas tanks, hoses wires, and whatever else that sinks. The website says hull weight is 2500 and displacement is 5100 so could I say maybe 3000 pounds for flotation so 50 cubic feet of foam would be enough?
"My mind is on a permanent vacation, the ocean is my only medication"

JimmY
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Re: Flotation foam

Post by JimmY » Sun Jun 23, 2019 4:43 am

I believe the displacement includes people, which float, so you don't need foam for them. I would try to estimate the weight of the stuff that doesn't float and add a little extra.

3000 lbs of flotation would be 50 cubic feet. That would be a block 7' x 7' x 1'. That sounds like a lot compared to Tom's 20 cubic feet.
-Jim
Nothing says poor craftsmanship like wrinkles in your duct tape!

TomB
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Re: Flotation foam

Post by TomB » Sun Jun 23, 2019 6:20 am

According to the trucking company, my engine and transmission weighs 1,000 lbs. I didn't weigh anything else and my guess of 200 lbs is probably low. The fishing gear and anchor may go overboard in an emergency. :D :D

You mention the fuel tank. I have a 33 gallon plastic fuel tank. Gas is a couple of pounds lighter than water. So full fuel, 66 lbs of buoyancy offsets the weight of the tank and empty would provide even more buoyancy. Batteries on the other hand...

I am using polyethylene (pool noodle foam) as floatation foam, Bill used polyurethane foam (car seat foam), most closed cell foam will work (chemical resistance gas and oil might take some out of consideration). I will be using polyurethane for seat foam and it will be part of my "safety factor".

Tom

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kens
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Re: Flotation foam

Post by kens » Sun Jun 23, 2019 9:18 am

I have the thought of empty air chambers under the decks.
since we are building a wood boat, with all the plans & patterns, we may be able to pattern a air chamber fitted between the frames, and bolted under the decks. Removeable for inspection and cleaning, and air provides good buoyancy. made out of thin plywood should do well.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

bobinpowayca
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Re: Flotation foam

Post by bobinpowayca » Sun Jun 23, 2019 5:39 pm

Howdy I built the geronimo and used pour in place foam extensively; I finished her (Aagatha) last April and have had her out about thirty times since then, almost always on San Diego Bay which usually has a chop on it.
First reason I did this is for flotation, don't have the numbers handy but I poured the foam between the deck and the hull everywhere except a 2'wide bilge from the forward most frame back to the bulkhead (2lb foam); definitely will float if swamped and we won't have to worry about being eaten by sharks while waiting to be picked up :lol: and it could be towed back.
Second reason - it made a really solid deck; i.e. when you walk on it it doesn't flex, and a neat installation - I got the 3/8 decking as close as I could to the hull sides and then quik-faired them to the hull. I can raise the bow of my boat and hose out the interior and what doesn't run out the motorbox gets pumped out of the bilge - real easy to clean the boat.
Third reason - I can get up to 38mph on the bay and with a slight chop the hull slams the water like you wouldn't believe - I feel better knowing the hull panels aren't flexing as much with the solid foam.
Another reason - if I should ever hit a rock or a piece of flotsam significant enough to puncture the hull - instead of the ocean rushing in and us sinking, I will end up with a "divit" in the hull - a puncture in the wood and divit in the foam- similar to a surfboard divit which can be repaired at home and not a catastrophic event.
So I used the two hole method and did one section at a time, usually between two frames and the bilge wall and hull side. Be careful and don't pour it in too fast or too much, once I did this and the foam reacts so quickly that the force busted the deck off the frame and hull and I had to remove it all and do over, lucky I didn't crack the hull. Bob
Attachments
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no foam can stop a recoilless rifle
IMG_1212.JPG
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only bilge area has no foam
Bob
_______________
Built the Glen-L 17 (1988), Geronimo (2018)
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psychobilly
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Re: Flotation foam

Post by psychobilly » Mon Jun 24, 2019 2:36 am

Any progress pics Weller? Sure would like to see some of the girl.

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weller
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Re: Flotation foam

Post by weller » Wed Jun 26, 2019 6:31 pm

After I get the foam in I'll post some pics. I decided to just make blocks out of the 2lb foam and put them everywhere I can. I think I can fit enough to float 2400# and I hope that's enough. Thanks for the help everyone
"My mind is on a permanent vacation, the ocean is my only medication"

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