3 ms·

Okay, lot of bad takes here. As a real-world sailor, here is how this works. A flag will only stream forwards in the special case of sailing dead down wind (DDW

Okay, lot of bad takes here. As a real-world sailor, here is how this works. A flag will only stream forwards in the special case of sailing dead down wind (DDW). An even in this case, the flag will tend to be limp as the boat will likely accelerate to close to the speed of the wind (dependent on length/hullspeed of the tall ship relative to wind strength etc.). Sailing ships don't often sail DDW because this is not the fastest point of sail. It is usually advantageous, and common, to sail at a slight angle to the wind. On all these other points of sail, the sails are bending the wind around the boat and there is a generally smooth, attached, laminar flow of air on both sides of the sail (if you are doing it right). Even square sails work like this, even though they are not an ideal airfoil shape. This mean the airflow is parallel to the sails. And the flag would also follow this direction and flow close to parallel to the sails as well. There is a concept of apparent wind. The flags will follow apparent wind which is the vector sum of the true wind plus the boat's velocity. That wind direction, combined with the sails effect of twisting the local wind direction, is the wind that the flag is experiencing. Generally the play testers are right, blowing straight forward is usually wrong. here is a picture of a flag blowing on a tall ship that is sailing across the wind: https://sailtraininginternational.org/app/uploads/2016/06/vessel-niagara-7.jpg https://sailtraininginternational.org/app/uploads/2016/06/ve...

pvillano 4y ago
A Pelton water wheel uses a similar effect as sailing perpendicular to the wind. A normal water wheel moves at nearly the same speed as the water and extracts little useful energy, like sailing DDW. Note that the energy of the wind is kinetic energy, so taking energy from the wind slows it down. A Pelton wheel has bowl shaped paddles that, like a spoon under a faucet, redirect the water into the exact opposite direction. The wheel runs so that the rim speed is half the water speed. From the perspective of a single paddle, the water is moving half as fast. From this perspective, the water hits the paddle and reverses to leave at the same speed. From an outside perspective, water hits the wheel and basically stops, transferring all its momentum to the wheel. Conservation of momentum also explains how Veritasium was able to ~sail DDW faster than the wind with a land propeller craft. The propeller spun fast enough to slow down the wind behind the craft, meaning energy was extracted.

pvillano 4y ago

A Pelton water wheel uses a similar effect as sailing perpendicular to the wind. A normal water wheel moves at nearly the same speed as the water and extracts little useful energy, like sailing DDW. Note that the energy of the wind is kinetic energy, so taking energy from the wind slows it down. A Pelton wheel has bowl shaped paddles that, like a spoon under a faucet, redirect the water into the exact opposite direction. The wheel runs so that the rim speed is half the water speed. From the perspective of a single paddle, the water is moving half as fast. From this perspective, the water hits the paddle and reverses to leave at the same speed. From an outside perspective, water hits the wheel and basically stops, transferring all its momentum to the wheel. Conservation of momentum also explains how Veritasium was able to ~sail DDW faster than the wind with a land propeller craft. The propeller spun fast enough to slow down the wind behind the craft, meaning energy was extracted.