I have a home made 16' sail boat. Its made of plywood and is covered with a single layer of glass cloth.No battery,no motor. Weighs about 600 pounds.I want to use 2 liter soda bottles as floation under seats, lazerete and bow area. How would i figure how many i would need to maybe float it about 2". Its a swamper and right now would probably float with only top of cabin above water.Maybe.Iam not sure.Is there a formulia?
Calculate Floation
- Thread starter Tom Erhart
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One liter is 2.2 pounds of water. The boat is 16 feet long and weighs 600 pounds. so it weighs about forty pounds per foot. Determine the average depth of the hull and divide that into 40 and you will have the weight per foot per inch of depth.. Then just figure the number of bottles needed to float that much per foot and multiply by 16 feet.
Tom, you may want to try to use as many 1/2 gal orange juice bottles as you can- they are square and will fit closer together with less lost (non-flotation) space between them. Just be sure they have screw-on lids. -Paul
Tom, I agree with Ross. If you want 10% of the boat above water you will need to supply 60lbs of boyancy. Fiberglassed plywood is about neutral so what is below the waterline can be neglected. 60/4.4 would be around 15 two liter bottle.
BTW, leave them outside your Illinois house with the caps loose overnight, then close the caps to hold positive pressure as they warm, so they don't collapse when under water.
BTW, leave them outside your Illinois house with the caps loose overnight, then close the caps to hold positive pressure as they warm, so they don't collapse when under water.
Spray foam
polyurethane foam fills All the voids and provides about 50 lb/cubic ft. You would need to balance the lift fore and aft but it beats loosing all that cabin space to bottles
polyurethane foam fills All the voids and provides about 50 lb/cubic ft. You would need to balance the lift fore and aft but it beats loosing all that cabin space to bottles
Polyurethane foams, at least the two-part ones, will eventually absorb water... not really a good idea for floatation foam.
Just to throw another monkey in the wrench, I found some high quality closed cell polyethylene flotation material at dollar tree. Fifteen cubic feet costs a shade over $100: http://blizzard.zmm.com/g20/noodles.jpg
I keep hearing people say this so I decided to do a search.
http://www.fomo.com/resources/technical-bulletins/Moisture-Vapor-Transmission.aspx
August, 2004
Moisture Vapor Transmission ("Perm" rating of Handi-Foam Two-Component PU Foam)
Water in its low energy state (liquid) does not permeate through polyurethane closed cell foam, and in its high energy state (vapor) its permeance is retarded significantly. Because of its very low moisture vapor transmission properties, polyurethane foam may be considered a 'vapor retarder', when applied in sufficient thickness, There is not a strict definition of what constitutes a vapor retarder vs. a vapor barrier. Furthermore, the outstanding insulating and air barrier properties of Handi-Foam Two-component Polyurethane Foam, when applied to form a seamless, monolithic coating make it an excellent solution to the problem of moisture condensation and humidity build-up in properly designed construction.
The most common method for evaluating the moisture vapor diffusion rate of a building material is ASTM E-96 (Standard Test Method for Water Vapor Transmission of Materials). E-96 determines the "water vapor permeance" for a given material at a given thickness. The permeance is often referred to as the "Perm rating"; the higher the Perm rating, the faster the diffusion rate of water vapor through the material.
Handi-Foam Two-Component Polyurethane Foam (UL94 Quick-Cure formulation) has been tested according to ASTM E-96 at varying thicknesses, and has a Perm rating of approximately 2.6 at a thickness of 1" (a Perm measures the number of grains of water vapor that pass through a square foot of material per hour at a differential vapor pressure equal to one inch of mercury. The metric equivalent unit of measure is 1 Perm= 57.45 ng/s.m2.Pa). As a point of comparison, open cell polyurethane foams typically have perm ratings between 10 and 50 at 1".
The 2000 IRC building code defines a vapor retarder
From one of the foam manufacturer's websites:
Based on this, it does appear that the material will absorb water if it is immersed in water for any extended period of time. Your quote is from terrestrial building applications, and isn't really relevant to the use of such a foam in marine applications IMHO.
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