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post #32 of Old 08-31-2013
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Re: Cat 25

Originally Posted by LakeMi View Post
So does that mean more speed or just more heel
Displacement hulls have a theoretical maximum speed. More sail power means more speed only until the boat hits its "hull speed." Once at hull speed, any additional power (from more sail area, or greater lift of the existing sail area) will just be wasted. There are a few ways a boat will waste energy - its stern could "dig in" and its bow rise, causing it to dissipate the energy through viscous friction; it could dissipate the power through turbulence around the rudder and hull; or it could dissipate by heeling over into a less efficient hull form in the water. Heeling also depowers the sail by reducing the sail area exposed to the weather by a factor of cosine of the heel angle. In other words, your boat is telling you, "if you won't depower your sails yourself, I'll do it for you."

There are several ways to depower, and you should practice all of them together. You can reduce sail area by reefing the main and partially furling the genoa (or putting on a smaller jib if you don't have furling), you can flatten the main sail with a vang and/or dropping the traveler and increasing tension of the main sheet and/or tensioning the outhaul, and you can "spill air" by letting out the boom. There are other ways to that more expert sailors can share.

In the example cited here, a blown out sail can't be sufficiently flattened (depowered) because there's too much curvature from the fabric stretching, no matter how much tension you apply to the sail.

Rick S., Swarthmore, PA
USCG Certified Captain, 50 Ton Master and OUPV
ASA Certified 101/103/104/105/106

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2001 Catalina 34MkII Tall Rig Breakin' Away, Universal Diesel M35B, Mantus 35 lb. anchor, sailing out of Rock Hall Landing Marina

Last edited by TakeFive; 08-31-2013 at 10:04 PM.
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