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A friend of mine emailed me this question:
Drafting in a car works because the rear car pushes a high pressure area in front of it, partially filling the low pressure area behind the lead car, reducing the drag for both cars. But do you have to be near directly behind for it to work? I'm thinking you do.
Canada Geese (and military aircraft) fly in v formation more for wingtip vortex reduction, iirc.
Boats on the surface work more like supersonic flow (which is what water tables are for), with little to no forward propagation of the pressure waves above a fairly low speed. So that makes me think that unless the boats are close enough for the trailing boat to push the little "pile" of water in front of it close to the lead boat, there will be no effect on the lead boat.
So a boat could ride the trough between waves or surf the bow wave, reducing its own drag while not affecting the lead boat at all. The biggest complication I can think of, though, is the effect of the propulsion. Power boats push water behind them, creating a high pressure zone, so if you sit behind a power boat, you'll be pushed backwards. A dragon boat is paddled, so you'd need to ride the wake far enough away that there is no adverse effect on your boat (or your boat's paddles). Either way, the trailing boat will not help the lead boat unless the trailing boat is so close horizontally that they are both riding each other's wakes.
I can't think of any situation anywhere where a trailer would actually slow down the leader.
Comments?
At first glance, I expected it to be easy, but I'm really not sure what the answer is!
Drafting in a car works because the rear car pushes a high pressure area in front of it, partially filling the low pressure area behind the lead car, reducing the drag for both cars. But do you have to be near directly behind for it to work? I'm thinking you do.
Canada Geese (and military aircraft) fly in v formation more for wingtip vortex reduction, iirc.
Boats on the surface work more like supersonic flow (which is what water tables are for), with little to no forward propagation of the pressure waves above a fairly low speed. So that makes me think that unless the boats are close enough for the trailing boat to push the little "pile" of water in front of it close to the lead boat, there will be no effect on the lead boat.
So a boat could ride the trough between waves or surf the bow wave, reducing its own drag while not affecting the lead boat at all. The biggest complication I can think of, though, is the effect of the propulsion. Power boats push water behind them, creating a high pressure zone, so if you sit behind a power boat, you'll be pushed backwards. A dragon boat is paddled, so you'd need to ride the wake far enough away that there is no adverse effect on your boat (or your boat's paddles). Either way, the trailing boat will not help the lead boat unless the trailing boat is so close horizontally that they are both riding each other's wakes.
I can't think of any situation anywhere where a trailer would actually slow down the leader.
Comments?
Clausius; as always, it's a pleasure to read your posts... especially in areas like this where fluid dynamics are involved. In this case, however, I'm not sure that your analysis matches the original question. Russ was asking about sculls or similar rowed boats. I can't see that gravitational interactions would have much effect. We're not dealing with jet boats or aircraft carriers or anything else exotic. It's probably closer to the interactions among adjacent swimmers.
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