DDWFTTW - Directly Downwind Faster Than The Wind

gonzo said:
Downwind means moving in the same direction as the wind. In that case, the wind speed is the maximum theoretical speed. However, because of friction and the force approaching zero as the vessel approaches wind speed, it is not attainable. Alan's diagram shows a typical technique to increase VMG. That is not the same as going downwind; it is broad reaching.
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By the same logic it is not possible to go upwind because it is impossible to sail directly into the wind, only sailing close hauled is possible.
But if it is possible to sail "upwind" by tacking between alternate close hauled courses it is possible to sail "downwind" by gybing between alternate broad reaching courses.
The important point is it is possible in some boats to make progress in the directly downwind direction faster than the true wind speed.
 
That is correct. However, the ground inputting energy into the system is nonsense. The ground get energy from the system through friction, heat, etc. There is a misunderstanding by several members of the difference between downwind and broad reach. One does not sail upwind, but work upwind tacking. Sailing upwind would be going to windward while in irons.
 
gonzo said:
Since the ground is stationary, there is no energy input from it into the system.
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Gonzo, you are much much smarter than this statement.

'Stationary', as you have pointed out, is just a matter of reference. What does the treadmill model tell us? Where is the energy coming from? Pull the plug.

A floating balloon has no energy nor does it extract energy from the air it floats in. There are no air molecules whipping past. One hour later, the same crowd of atoms are still having their cocktail party together with the balloon. The ground isn't invited to the party.

We crash the party and bring the energy when we impose a frame of reference by comparing the relationship of the air to the ground or to the water.

I'm not saying anything that you haven't already said. Why would you refer to the ground as stationary when someone is trying to change the frame of reference to the air? They are basically converting the problem to the treadmill model. That is very reasonable.

-Will
 
I mention it because they use the air as frame of reference, and then use the cart as frame of reference. That is incorrect.
 
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