Not quite. If you get a chance, watch carefully when a tug or pilot
boat approaches a big ship at, say, 15 knots. The tug is hurrying
along like mad, throwing a huge bow wave, while the big ship is just
gliding effortlessly through the water. When the tug gets within a ten
or twenty feet of the big ship, suddenly it, too, is gliding along
effortlessly as it has become part of the big ship's wave pattern.
Tugs have to be careful at this moment because the power required goes
down dramatically.

Your dinghy may not do it, but it is possible to fool the water -- the
Kiwis tried it in the last America's Cup

Now for a standard rant of mine. There is no such thing as "hull
speed". If you look at the math, at tank tests, at rpm curves, or at
actual fuel consumption of displacement vessels, there is no
inflection, change, bump, or anything else in the power versus speed
curve at S/L 1.34. Sure, the power required and fuel consumption are
going through the roof, but it's a smooth curve. If you apply more
power, you will go faster, to the point at which the power applied
exceeds the integrity of the boat or the size of your wallet.

If you doubt this, ask any destroyer sailor. They regularly exceed
S/L 1.34. An Arleigh Burke destroyer is 466' LWL, 32 knots maximum
speed, for an S/L of 1.48. Of course it takes almost 12hp per ton to
get there.

Jim Woodward
www.mvFintry.com



Jere Lull wrote in message .. .
Parallax wrote:

Does towing my hard shell dinghy effecively increase my waterline
length thereby increasing my hull speed?


no

Could you add a lightweight inflatable extension to the waterline of a
boat to increase its waterline length thereby increasing its hull
speed?


probably not, as it has to support the boat. What you're describing
would probably just deform and not change your effective LWL. Its drag
would probably erase any benefits.