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Author Topic: The Dole Derby  (Read 117309 times)

Gary LaPook

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Re: The Dole Derby
« Reply #195 on: April 22, 2012, 04:57:06 PM »


A modern, well designed sailboat with a tall, high aspect ratio sail plan can sail within 45 degrees of the true wind. Square rigged vessels could only sail within about 70 degrees of the true wind so do not make much progress against the wind. But what makes sailing upwind possible is a keel that acts like a hydrofoil making lift under water.  So it was not the lateen sail that made sailing close to the wind possible but that in combination with the keel. Life rafts do not have tall sails (if they have sails at all) and they do not have keels which is why they can only sail about straight downwind, more than 170 degrees away from the true wind for large rafts and straight downwind for a small raft.The sail and keel combination extracts energy out of the air/water system which propels a sailboat. A balloon cannot extract energy from the movement of the air mass, the wind, it can only travel with the air mass, straight downwind, just like a life raft. A windmill can extract energy from the  movement of the air because it is anchored to the ground and cannot be blown downwind and a sailboat, with a keel which prevents the boat from being blown straight downwind, can also extract energy from the movement of the air at the interface with the ocean and so be propelled in about 3/4ths of the compass, only excluding the 90 degrees surrounding the direction of the true wind.

gl
To make sure that I had it right about life rafts being blown only straight downwind I decided to ask an expert on the behavior of life rafts so on Saturday I asked:

"So, Mr. Zamperini, based on your knowledge of life raft performance, how much can you make them sail away from straight downwind, ten degrees or twenty or thirty?"

"Don't be ridiculous, you go straight downwind, that's the only way you go. We could tell when we passed by flotsam that we were moving through the water in exactly the opposite direction from the wind."

"Thanks, that helps, and thanks for your service."

gl
« Last Edit: April 22, 2012, 05:00:26 PM by Gary LaPook »
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