Flotation Needed?

[dbuffington]

Hi Folks!

I'm working on our 1957 Whirlwind runabout, and while I have some things apart, I could add some flotation. Currently, there's none.

But is it necessary? Here are the details...

The boat is approximately 16 foot long, and it's made of molded plywood. (It's a technique, popular in the 1950s, in which very thin strips of resin coated mahogany are overlapped on a mold and compressed using heat and vacuum.) According to the manufacturer's specs, the hull weighs 525 pounds.

The motor is a 1957 Mercury Mark 55e. I'm guessing the motor and battery weigh no more than 200 pounds.

Throw in another 100 pounds of junk, and you have a total weight of 825 pounds.

Anyone out there capable of doing the calculations?

Thanks!
Dave

 

[Bob_VT]

Re: Flotation Needed?

In the restoration section there are multiple Foam Calculations in this post http://forums.iboats.com/showthread.php?t=288451 I will move this.

 

[erikgreen]

Re: Flotation Needed?

Are you asking about whether you need to install foam, or what, exactly?

You can almost ignore the hull, it's wood and not that dense. A hundred pounds of floatation would probably keep it on the surface. The motor would have to be compensated for obviously. I'd guess you'd need about 350 to 400 lbs of floatation to ensure if swamped the boat would at the surface and let you cling to it.

That's an equivalent volume of 400 lbs of water to displace. Water weighs 62.4 lbs per cubic foot roughly, so doing the math that's 6 1/2 cubic feet of foam you need. Not that much, but do you have space to put that somewhere?

Your boat is old enough to not legally need foam installed.

That construction technique is called "cold molding" and it's still in use for producing certain components today (and in fact to produce plywood, which most of us here use).

Erik

 

[dbuffington]

Re: Flotation Needed?

...so doing the math that's 6 1/2 cubic feet of foam you need. Not that much, but do you have space to put that somewhere?

Your boat is old enough to not legally need foam installed.

Thanks, Erik!

I know it's not legally required, but I don't want my baby to sink either

And best of all, there's a wonderful, unused and concealed space under the rear seat that's probably just about exactly 6 1/2 cubic feet. Heck, I could just stuff it full of swim noodles

Thanks again!
Dave