# Windmills on a boat

Discussion in 'Projects & Proposals' started by Gravio, Feb 23, 2020.

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### Will GilmoreSenior Member

what if the propeller operated as a pair of sails instead of a fan? Would there be any need to connect the propeller shaft to the wheels? The blades would act as the two sails in the concept video of the sailboats traveling around a cylindrical Earth, but they would be connected and drag the connected vehicle along on their journey. They just need something to act as the lateral resistance of the keels.

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### DejaySenior Newbie

Sorry I'm confused what you mean Will.

In the veritasium video the explanation is at 17:24. The wheels drive the propeller which acts as a fan to push back against the wind, which increases the maximum speed that can be extracted from the wind to something like 2.4 times. So for a boat the propeller would have to drive the windmill as a fan.

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### Will GilmoreSenior Member

Yes, but there is an explanation of the theory that uses a computer animation that shows two sailboats sailing on opposite sides of a cylindrical Earth. They are being driven, as sailboats are, by a wind moving parallel with the cylinder while they sail at a close reach around the cylinder. They have their keels in the water, of course, and their sails look and act like the windmill blades traveling into the wind.

If the two sails were connected through the base of their masts, why would they need the wheels to drive them? Could they simply sail on their close reach in a spiral and drag any vessel attached at their hub along with them?

The vessel being pulled along would see an apparent wind that stopped or came from the head (the VMG), but the rotating sails would see a different apparent wind, that which was typical of the reaching sailboat.

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### Will GilmoreSenior Member

perhaps the difference in apparent wind near the hub and the apparent wind at the tips would be irreconcilable.

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### DejaySenior Newbie

Ah sorry I somehow missed that part. It's at 8:00.

Ok now I understand but I don't know. I believe a sailboat on a broad reach still cannot go faster than the wind speed along the direction of the wind. Even if sees much more apparent wind.

So you would need to connect the wind blades to the propeller to push faster than wind speed. In your example the two keels of the connected sailboats could act as a propeller though.

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