Inertia, Mass, Resistance, Pitching??

Inertia, Mass, Resistance, Pitching??

Postby Admiral » Tue 01 Sep 2009 - 10:40

pitching: the angular rotation of a moving body about an axis perpendicular to its direction of motion and in the same plane as its top side

I've noticed all boats starting to "bob" over the waves, when wavelength is shorter then the boat length.
It would seam that the boats have no inertia turning around the Z-axis (horizontal and perpendicular to its direction of motion). With the VOR-70, the Bavaria 36, DY 40, Valk, and I would say 470 and Laser too, but maybe somebody with some real experience, can give an opinion on that. The pitching (nl: stampen) of a boat means at least half her mass is moving up and down, add to that the mass of the water that has to be displaced by the submerging stern or bow and pitching should be dampened, by inertia and the displaced water.

Also any boat designer will try to absorb that movement by all possible means (loss of energy, in useless movement). I'll make an exception for purposebuild downwind sailing boats there they may have other priorities, as the VOR's breaking up in the chinese sea would proof, but even the VOR 70 in sailsimulator to me seam to pitch too violantly in waves that are around her boatlength or shorter, even sailing downwind ).

I also noticed that the boats can stand a lot of wind without penalty, leading to situations, where when sailing under displacement conditions (as apposed to surfing), boats will start to climb their bow-wave, curiuosly however the stern does not sink away like i would expect from a VOR 70 with water ballast in stern tank and all weight moved to stern, or a 5 and a half ton (empty) Bavaria 36, in effect it looks as if the stern is lifted, where the rudder leaves the water almost completely. I think when a boat starts tilting forward on her bow-wave and the rudder becomes exposed, a very violant broach would be unavoidable.. at the moment i can sail the bavaria 36 for instance with the rear half out of the water quit comfortably, even if it starts to yaw a bit.
A Valk wil start to glide, surf, or turnover, but at no time will she lift her stern out of the water, that i noticed ....

Is anybody else having an issue with the pitching in Sail Simulator 5 up until at least version 5.0.5.4?
"As far as I can remember, there aren't a lot of points of land or holidays named after people who sat at home and criticized Christopher Columbus."
(Paul Cayard, from the Pirates base, in an e-mail to race HQ. 25 Jan 2006 volvooceanrace.org)
Admiral
 
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