On Fri, 24 Sep 1999 JBlumhorst@aol.com wrote:
> In a message dated 9/23/99 7:54:34 PM Pacific Daylight Time,
> TillyLucy@aol.com writes:
>
> > In the recent thread on how big a motor to put on a P-19 several folks have
> > mentioned that one should go to a higher horsepower motor if sailing in an
> > area where there are high currents. I'm confused by this, isn't a current
> > just moving water? It seems to me that if the boat is equipped with a
> motor
> > that will drive it at hull speed there would be little benefit in using a
> > bigger, heavier, more expensive one. A hull speed in still water of 5 kts.
> >
> > Dave Kautz
> > P-15 #!1632 Tilly Lucy
> > Palo Alto, CA
> >
>
> There is an online calculator for hull speed (using Dave Gerr's formula for
> displacment and semidisplacment hulls) and horse power at
>
> http://www.yachts4sail.com/hullspeed.html
>
> Accroding to the calculator, it takes 6.7 hp to drive a 2000 pounds (loaded)
> P19 with an LWL of 16.25' at hull speed of 6.3 knots.
>
> To make hull speed with an opposing wind, you'd need more than 6.7
> horsepower. As you pointed out, an opposing current doesn't enter into the
> pciture..
>
> Best,
> Judy B
Let's not forget that "hull speed" is not the boat's maximum speed, just
the speed at which it takes proportionally more power to increase its
speed. For the Potter's flat bottom design, this is probably quite a bit
less (proportionally) than a more typical displacement hull design.
Believe me, when you get into a 7 or 8 knot current, whether it is due to
river current or tides (or both combined, as we have around here) you want
all the power you can muster.
Rich Gort
(Still waiting for that perfect motor to be made available)
WWP19 #202 SAYOKO (Oct, 83)
Lake Stevens, WA
Sailing Northern Puget Sound and North Cascades Mountain Lakes