I would assume that there must be some relationship between windage, righting moment, steering and leeway resistance that would define if a boat can go upwind in any weather. It is the windage that I would assume becomes the major issue as the wind goes up to gale force or higher. If the driving force of the sail does not exceed the wind drag of the boat, it won't go upwind. So, should I be calculating the maximum sail area for the righting moment at 40 knots of wind, then compare that to the force of the wind on the cross-section of the boat? I don't know the formulas for that.
Your description is nice and shows the boat as safe and comfortable, but I don't see how it can be used to predict if it will actually sail upwind.- Gardner
It can't. There are too many variables to calculate it accurately enough, but could be a fun exercise to try. Assume drag coefficient of 1.1 (this is for a flat plate, will actually be less) for the hulls, crew and the bits of the mast without sails. Align this at 40-45 degrees to the wind (you will be lucky to point any closer than this in 40 knots) and use the formula Drag = Wind speed squared x Cd x density of air x surface area.
Drive from the sail is the same, except with the coeff of lift rather than drag. For a cloth sail in 40 knots, this will be less than 1.
Drag from the hulls and foils, no idea, but in the order of some 10's of kgs.
righting moment is weight in the ww hull x centreline to centre line beam.
Capsize moment is height of coe above the water x sail area. Breeze to fly a hull see Shuttleworth on Seamanship.
Leeway resistance is wind loads on everything above the water, plus the forces from the sails, vs the resistance to going sideways from the foils and hulls.
Remember the wind to use is the apparent, which will be more than the true.
Good luck, be interesting to see the results.
On Tue, Mar 22, 2011 at 9:28 PM, Rob Denney <harryproa@gmail.com> wrote:On mine, I said
UPWIND IN 40 KNOTS
The simple, forgiving rig, very high righting moment, shelter on the windward side and lack of things to worry about should make it as easy as possible for the crew. The large, twin rudders and schooner rig give excellent, low stress control at low speed with no flogging sails or sheets. Windows in the cuddy allow a seamanlike lookout to be kept without exposing the crew. Shunting really comes into it's own in these conditions, particularly if there are big waves as well.
Use what you like, but probably diplomatic not to use an exact copy. I explained about simple forgiving rig, lack of worry, etc elsewhere.
robOn Tue, Mar 22, 2011 at 10:29 PM, Gardner Pomper <gardner@networknow.org> wrote:
Part of the wooden boat design competition is the ability for the design to sail to windward in a gale. How can you prove that from a drawing? I am pretty sure that my design will float, and it should be fast, but I don't know how to calculate upwind performance in heavy weather. Can anyone tell me what criteria might be used to judge that?- Gardner