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West Wight Potter Mailing List maintainer
dfarrell@ridgecrest.ca.us
List hosted by www.tscnet.com
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Alan (or is it Marilyn?)
Virtually all trailer sailboats have capsize screening ratios over 2.0.
According to the screening test, they are "vulnerable in the event of a
capsize" (The number does not imply that they are vulnerable to capsizing,
but vulnerable after capsizing)
The capsize screening formula has nothing to do with the stability of the
boat. It was developed 10 years ago, after the Fastnet Race Disaster - to
screen for boats that wouldn't return upright easily after a 180 degree
knockdown.
It is a "merit" measure of the boat's ability to come back from a 180 degree
capsize. It should be ew-named the "capsize recovery metric" : ) It is a
useful metric for ocean-crossing boats that are likely to get caught in
Force 8 or Force 10 Gales with huge waves (high wind in a storm isn't
dangerous to the good skipper, but large waves can flip any boat). It
really isn't a useful metric for most trailer sailboats intended for coastal
cruising.
Most sailboats depend on a combination of keel ballast and a wide beam for
stability. Wide boats have good initial stability, but once they're upside
down 180 degrees, they are also quite stable in that position due to the
wide beam. That's a characteristic of almost all sailboats under 26-28 feet
long and under 4000 pounds (which would be very lightweight-to-average for a
28 foot cruiser).
The capsize screening formula is:
Beam dimension in feet divided by the cube root of Displacement expressed in
cubic feet of sea water (64 pounds per cubic foot).
Therefore, a 1200 pound boat displaces 18.75 cubic feet of seawater and the
cube root of 18.75 is about 2.65. In order to have a good capsize screening
ratio value under 2, the beam would have to be 5.3 feet. That's too narrow
to for the boat to be comfy or have a usable cabin.
Another way to look at it: Say you want a boat with a beam of at least 7.5
feet. In order to have a "capsize recovery metric" of 2 or less, it would
have to displace 43 cubic feet of seawater and weigh a minimum of 2700
pounds.
Truth is, there aren't too many trailerable boats that can measure up to
this metric. The only one I know of is the Flicka, a 20 foot, 6000 pounder
with a deep, full keel. I'd call that transportable, not trailerable. You
gotta keep that heavy beauty in the water most of the time or have a very
big truck and a crane. In fact, until you get into the 34 foot range (or at
least 28 feet), there are almost no production trailler sailboats that can
pass this "screen".
The Potters aren't true ocean-crossing boats -- and we knew that. They
don't measure up to the capsize recovery metric. Don't sail a Potter in
conditions where you will be hundreds of miles off-shore in 50 knots wind
with 30 foot, breaking seas :)
Fair winds,
Judy B
> -----Original Message-----
> From: Marilyn Dimson-Doyle [mailto:mddoyle@mediaone.net]
> Sent: Monday, February 14, 2000 9:32 AM
> To: potter
> Subject: Form posted from Microsoft Internet Explorer.
>
>
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> West Wight Potter Mailing List maintainer
> dfarrell@ridgecrest.ca.us
> List hosted by www.tscnet.com
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> lengthwaterline=16.9
> lengthoverall=18.9
> displacement=1225
> beam=7.6
> sailarea=135
> category=racer
> capsizeratio=2.84
> speed=5.5
> SailAreaToDisplacement=18.86
> DisplacementToLWL=113
> LengthWaterLineToBeam=2.224
> MotionComfort=7.21
> description=Capsize Ratio: A value less than 2 is considered to
> be relatively good; the boat should be relatively safe in bad
> conditions. The higher the number above 2 the more vulnerable the
> boat. This is just a rough figure of merit and controversial as
> to its use.
> OwnerName=Alan Dimson-Doyle
> BoatType=Potter 19
> BoatName=Still Looking
> mail=wwpotter@tscnet.com
>
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