Also, an oft overlooked point in adding floatation is the upward force
generated by the buoyancy of the foam when the foam is submerged as in a
turtle maneuver. If the foam can break free of its restraints and bob to
the surface all by itself it will. I don't know if the cabin liner in a
Potter is strong enough to restrain 200-300 # of buoyant force; so I'd think
carefully just where I was putting additional floatation.
Regards,
Mac Davis; WWP19#804, Kelpie, Aripeka, FL
-----Original Message-----
From: JBlumhorst@aol.com <JBlumhorst@aol.com>
To: wwpotter@tscnet.com <wwpotter@tscnet.com>
Date: Tuesday, May 04, 1999 9:58 PM
Subject: Re: How much Flotation? And Where?
>- - - - - - - - - - - - - - - - - - - - - - - - - - -
> West Wight Potter Website at URL
> http://www.lesbois.com/wwpotter/
>- - - - - - - - - - - - - - - - - - - - - - - - - - -
>In a message dated 5/4/99 4:35:10 PM Pacific Daylight Time,
>david_kautz@hp.com writes:
>
>> Question #2: If a boat had a lot of addtional flotation, particularly
>> low in the boat as in the bilges and under the cockpit floor (places
>> where Bernie is proposing to add it), could that make the boat MORE
>> prone to turtling and more difficult to right once inverted. It seems to
>> me that if the boat was on it's side and was entering the cabin,
>> flotation in the bottom of the boat would actually _encourage_ the boat
>> to continue over into the inverted position whereupon the flotation
>> would make it very stable upside down.
>>
>> Would it be wiser to place flotation high in the boat, like behind the
>> cockpit seat backs to encourage a "right side up" attitude?
>>
>Hi David,
>
>I think you're on the right track here. A few books I've read have said
that
>positive floation should be located as high up as possible. If you can't
put
>it on the cabin roof (who can spare any of that precious headroom?!?) they
>recommend putting half on each side at the widest beam right under the
deck.
>That way, half of the total foam exerts a righting moment if the boat is
laid
>over 90 degrees on its side and swamped. If it's upside down, it will be
>easier to right it if you can just get it tipped over a little.
>
>As to how much, sea water weighs about 64# per cubic foot. My P19, weighs
>about 1275 and fully loaded with gear, weighs probably 1800#. So about 28
>cubic feet of foam should easily dispalce enough water to keep the boat
>afloat. Bruce at IM told me they put in more than that in the new boats
(32
>cubic feet maybe, I forget). In fact, less than 28 or 32 cubic feet will
do
>the job, since fiberglass is less dense than water (the boat itself
displaces
>water). I'm assuming the crew is wearing PFD's or has them on board and
>therefore requires no added flotation.
>
>When I bought my new/old P19, there was much more than 32 cubic feet of
>styrofoam in it. I measured the volume at the back under the cockpit, and
>under the quarter berths (where the newer boats have sizable shallow
lockers
>for storage) and figured out how much was in there. Then I removed quite a
>bit from under the vberth until the total was a little over 30 cubic feet.
>More than that just takes up valuable storage space without adding any
safety
>to the boat.
>
>Best,
>Judy B
>
>Judith Blumhorst, DC
>HMS18/P19 Fleet Cap'n, Potters Yachters
>1985 WWP19 #266 Redwing
>Sailing on SF Bay, CA
>(5-35 knot winds, 2-4' chop, 2-6' swells, and currents up to 6 knots)
>Visit <A HREF="http://members.aol.com/jblumhorst/HomePage/index.htm">Judy
B's
>West Wight Potter Pages
></A>
>and <A HREF="http://songbird.com/potter_yachter/">The Official Web Site of
>the Potter Yachters
></A>