Foam under sole?

[Ike]

I used to manage the USCG's flotation testing program, testing new boats for compliance. Over the years I've seen a lot of things. Of course 99.9% had foam or air chambers. But my favorite was milk bottles.



This boat failed, but only because the bottles had metal caps that rusted out. When we flooded the boat, some of the bottles filled up. If they had used plastic caps, glued to the bottles, this would have worked fine. I have seen ping pong balls, microballons, beer cans (yep, aluminum beer cans) air bags, and a variety of other innovative ideas.

Oh yeah, i forgot to answer the other question: in the USA, Canada and the EU the limit is 6 meters (20 ft in the US.) 20 feet and up, flotation is not required. Some builders put in flotation up to about 26 feet but as the boat gets bigger it becomes impractical to provide enough flotation. Besides statistics show that the problem is with the little boats, not the bigger boats. Not that bigger boats don't sink, but the swampings and capsizings are far more numerous in little boats. The exception is France. I have seen 40 foot sailboats from France with flotation. On bigger boats it's easier to put in watertight bulkheads and have bigger pumps, double hulls and other ways of keeping the water out. Also its only monohull power boats. Catamarans, sailboats, inflatables, canoes and kayaks are not required to have flotation.

[alan white]

I'm rebuilding a sailboat right now, 19 ft and 1300 lbs weight (approx. 2000 displ.).
The only flotation will be 64 oz (two liter) plastic bottles. I'm figuring on 2000lbs worth, whic is overkill, but doable under the seats, which are long and deep. each bottle will displace about 4 lbs of water, so I'll need 500 of them. Even buying them for 8 cents (what the redemption centers sell them for), the cost is only $40.
I believe that those bottles are better flotation than foam. The reasons are:
They weigh less than foam.
They are cheaper.
They are easier to fit.
They offer an amazing redundancy--- they do not hold water unless they leak, a one-in-a thousand scenario.
They allow better airflow (bottles COULD be put in the bilge if necessary).
They are the best way to recycle--- through reuse without melting the plastic down.
Why would anyone use foam unless absolutely necessary?

[Ike]

Manufacturers use 2 part foam because it's cheap and easier to install. You can put it in any empty space without worrying about the shape of the space. With block foam or other methods (except air) you have to think about the shape and volume of the space. a 2 liter bottle displaces about 4.5 pounds (2.04 KG) So you would need about 5 bottles per person . To figure the number for the boat and machinery you need to separate the hull weight from the machinery weight. Aslo you do not use the actual weight of the hull or people, or anything that has it's own buoyancy. You need a factor to multiply them by to get the weight to use. the exception is engiens and drives. Then you use the actuall dry weight.

It would be the hull weight times a factor for the material (fiberglass is 0.33) divided by 4.5 to give you the number of bottles. e.g. the boat weighs 900 lb
900 x 0.33 /4.5 = 66)

The machinery would be the actual weight divided by 4.5 (e.g. machinery weight 400, 400 /4.5 = 89 bottles)

You can subtract bottles for things like wood and sealed compartments and foam cushions that won't float free.

see here http://newboatbuilders.com/pages/flotdiag.html

[DianneB]

I decided to forego the flotation for now. When I replace the front half of the sole next winter, I will reconsider the pros and cons.

The rear 2 sections of the sole have now been replaced (sans foam) and for anybody who is interested, there are pictures on my web site

http://diannebest.007gb.com/sylvan/sylvan.html

[missinginaction]

Good for you Diane and best of luck with that restoration. It's really nice to see a woman taking on tasks like these. We need more people like you in this world.

Best regards,

MIA

[DianneB]

Well gee thanks Missing!

"A woman taking on tasks like these....." ????

Well I want it done RIGHT - that's why I am doing it myself!