Ok Neil, Guess you are right about the CB being below the waterline. Had to google it. I was considering the entire hull as having volume and reserve buoyancy beyond the displacement value. I learned that that volume above the waterline doesn't apply to CB until it is wet, like when a wave lifts the stern and turns the boat.
Chuck Resolute 1990 C&C 34R Atlantic City, NJ ----- Original Message ----- From: "Neil Gallagher" <njgallag...@optonline.net> To: cnc-list@cnc-list.com Sent: Thursday, December 5, 2013 10:25:46 PM Subject: Re: Stus-List Now Stability - was List halyards again( 10 alof=1on the rail ) The notion that the CG must be below the CB is completely correct for a submarine, because a submarine has no waterplane, and so the CB does not shift to the low side when it rolls or heels. In that case, the center of gravity is like a pendulum under the CB and that, and that alone, gives a submerged body stability, or more correctly it will roll to the angle such that the CG is under the CB. The difference for a floating boat is that it has a waterplane with vertical or even outward sloping sides; this means that when it heels, the low side picks up more buoyancy while the high side loses some, making the CB shift sideways to the low side. This gives it the righting moment. The more it heels, the farther the CB shifts to the side, up to the point where the deck edge immerses. Actually, now that I think about it, the best example may be a floating cylinder: its waterplane does not change when it heels or rolls, so it will not have a shift of CB, and just like a submarine, it will roll until the CG is under the CB. However, any conventionally shaped hull can, and most do, have the CG well above the CG, including yachts. So it all comes back to the shape of the hull, thus the "form" stability name. Chuck, no offense, but it's physically impossible for CB to be a foot above the waterline, while displacement always equals buoyancy, as per Achimedes. For a racing yacht with a 50% ballast ratio the CG of the keel alone may be 4' below the WL (my 35-1 is 3.5' below WL, per keel drawing), but the CG of the other half of the weight, including rig and sails, is well above the WL, which typically puts the total CG just about at the WL, thus above the CB. There are some yachts that have CG below CB, but it's not a requirement for positive stability. Neil Gallagher Weatherly, 35-1 Glen Cove, NY
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