RE: Maximum efficient displacement hull speed - P19 hull speed

Eric Johnson (eric@theftnet.net)
Wed, 7 Oct 1998 09:24:58 -0700


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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> Basically, the
> Potter is limited by it's displacement to length ratio (DL).
> Being a light
> displacement vessel with an almost flat bottom should
> theoretically allow it
> to achieve and exceed high end of this range (1.6x WLL) for
> extended periods
> of time, while traditional heavy displacement wine glass hulls (Alberg
> Typhoon, Island Packet, Pacific Seacraft, etc.) would wallow in their
> troughs...

>
> With its biaxial glass, a displacement of 1300lbs and a waterline

>Dry< weight is in the neighborhood of 1300lbs. Displacement is another
thing altogether - I'm sure my boat, even when stripped down for racing,
displaces at least 2000lbs (ok, my crew and I are big!) I have to keep the
motor and battery attached since its usually after dark on my returns.

> length of
> 16'9" the P19 has a DL ratio of approximately 80 making it an Ultra light
> displacement sailboat (ULDB). The first ULDB, Windward Passage
> (DL=100) was
> built in 68'. Windward Passage beat every other sailboat of it's time for
> almost 15 years.
>
> If you take out the 1,200 lbs of extra "can't live without" gear
> we stick into
> our Potter19s,

like crew? :)

>throw that Putt Putt in the drink, get rid of that huge
> battery, move the crew forward and put some nice racing sails
> (large spinnaker
> anyone?) and a masthead rig on, it should be a fast performer capable of
> exceeding that 1.6 for long and extended periods...

You have a better grasp around the theory than I do, and I appreciate your
comments. The modifications you describe would make the boat not be a P19 in
anything other than hull shape. In the real world, the empirical data
suggests 5.5 is achievable nearly indefinitely provided a fair wind and
large enough sails (its actually remarkably easy to achieve with the genoa
and a stiff breeze), but I don't think anyone here has held a higher speed
than that for any appreciable length of time. My GPS once reported I was
holding an average speed of 6 knots for about 10 minutes. The long time
period and averaging should be enough for GPS errors to cancel. This was an
add situation where a low spit of land upwind kept the water calm but the
wind stiff.

The difficulty of measuring speed with inexpensive units adds to the
confusion. I might break down and eventually buy one of those fancy
knotmeters that reads to the 100th of a knot.

I'd had a heck of a time getting enough weight forward to help, but I do
agree it does help quite a bit.

> Notwithstanding the safety record of ULDB's (Transpac, Around the
> world) we
> have hundreds of sailors that swear that heavy and slow a la
> "Island Packet"
> is better than light and fast a la "Windward Passage"...

Well, >better< is a subjective term and really requires knowledge of the
purpose for which the boat is intended. The light weight (and therefore easy
trailerability) makes the P19 better for me, but I'd definitely prefer a
heavier displacement boat for any long open ocean voyage, if for no other
reason than seakindliness.

> Since
> many of these
> "sailor's" do most of the writing, in sailing mags, they continue
> to expound
> their "heavy and slow" theories while ridiculing all the speed and safety
> records established by ULDB's. Their gospel remains that the only
> boat worth
> having is a heavy ponderous crab crusher limited to less that
> 1.34 x WL Length
> with a DL of 300 or more... To fit their ends they publicly claim
> no sailboat
> can exceed this limit. They have done this for so long and so loudly that
> almost everyone believes them... Woe to anyone that does not agree...

True. Ever seen a Melges 24 sail? Thats gotta be a ULDB, faster (especially
in acceleration) than anything I've ever seen. Its amazing to watch them
tack at high angles downwind; the increased apparent wind they generate
doing so makes up for the longer distance they travel. This is true for many
boats (though not potters AFAIK), but on the Melges it is taken to an
extreme.

> Now, Off the pulpit, back to the Stock Market and the soothsayers
> of doom at
> CNBC...

heh heh I'd rather discuss sailing! :) I'd love to hear what anyone else has
found to improve speed. I did finally get a genoa, but haven't raced it yet.
I will race across Puget Sound in the Rum Run on Nov. 7th, so I'll get a
chance to try it then.