This discussion relates to speed limitations of small catsailor hulls.
We all agree that wave drag is one of several components of total resistance. In very light and slender catamaran dinghys, it constitutes a small component at low speeds. However, wave drag does increase significantly when the boat travels faster than the velocity of the waves it generates.
Wouter stated that
“wave-inducing drag it is something like 10-15% of the total”.
He proposed a doubling of wave drag with increasing speed over the wave velocity (“Now, you can easily double 15% and have the beach cat hardly notice much difference”).
Do we really know this number? We do not know whether it actually increases by a factor of 5 at 20 knots
http://www.boatdesign.net/forums/attachment.php?attachmentid=18865&d=1203073097It has been proposed that wave drag is of similar magnitude as viscous drag in kayaks already at 7 knots!
http://www.oneoceankayaks.com/kayakpro/kayakgrid.htmI tend to believe (and agree with Wouter) that surface drag is more important than wave drag in our cat dinghys. But a major question is whether wave drag of displacement hulls constitutes one (of several) significant limiting factor in attaining high speeds.
My experience has been that it is nose diving that has stopped us from sailing faster than 20 knots. Like Wouter, I think T-foil rudders are promising (next X-mas, Santa?)
Attitude:
Wouter, I really do appreciate your contributions to this forum. Many of your posts are helpful.
But why do you always seem to respond in a condescending way?
One example among many:
Quote: “as you gave a typical tortured reasoning that is often expressed by persons who keep clinging on to Froude's law as a predictor for maximum speed”.
This was to a post that did not even mention maximum speed, and to a person who has no interest in defending Froude or any other of his time.
You tend refer to science. This is good, we look for state-of-the-art knowledge. However, a typical characteristic of almost all scientists who publish in leading international peer-reviewed journals, is that they never exhibit condescending or arrogant behavior during scientific discussions.
A respectful approach to colleagues is also very productive in developing better equipment and skills.
When it comes to hydrodynamics of hulls and foils, a lot is empirically derived knowledge rather than formulas.
We need more empirical data.
Stein
