Should be easy:

A river runs straight from West to East at 10 knots. A 10 mile race is held: the boats sail downstream, from West to East. The first heat is held in the morning, when there is no wind. The second heat is held in the afternoon, when there is a 10 knot wind from the West. In which heat are the faster times recorded?

The morning. All motion is relative. In the afternoon you're sitting in the water with no wind and the finish line comes to meet you in 1 hr. In the morning the finish line comes towards your position in the water at the same speed, but you have the option of uphauling and beating into a 10 knot breeze to meet it.

Easy, you were actually in the bar all afternoon cause there wasn't enough wind to have a good sail and you ended up too drunk to care.

OK, so the river runs straight but you didn't say the race was straight so what if the course was a slalom style course down the river. So in the first race the boats may have sailed the course with apparent wind and scored a time. The second race was all DNFs as no-one was able to make it across the river to round the buoys with the zero apparent wind.

Wouldn't bet my shirt but I'll guess the first race.

Gonewindsurfing247 said...

Ok, I'll be the first goose to have a crack....

Both heats record the same time?

Reason: In 2nd heat the wind is blowing at same speed as the current making the apparent wind 0 and therefore identical to the first heat.

Correct

Are we windsurfing or kiting?

Mobydisc said...

If the sailors in the second race are using formula gear they would win.

How Moby, they mst be becalmed, river running at 10 knots and wind blowing at 10 knots same direction?

DL said...

Mark _australia said...

Gonewindsurfing247 said...

Ok, I'll be the first goose to have a crack....

Both heats record the same time?

Reason: In 2nd heat the wind is blowing at same speed as the current making the apparent wind 0 and therefore identical to the first heat.

Correct

Incorrect. Reflex films got it right.

First race has apparent headwind, so you go slower than the water speed.

Answer to puzzle.

The faster heat is the one with no wind. When the wind and the water both move W to E at 10 kt, the boats drift down the river at 10 kt, with their sails hanging limp. In the heat with no wind (as measured on the land), a drifting boat has a headwind of 10 kt. You can tack into that.

Of course, you don't get something for nothing. In the heat with wind, the river does very little work on the boat. In the heat without wind, it exerts much greater force on the boat, in particular on the keel or centreboard. Much of that work goes into disturbing the air downwind of the boat's sails.

Gestalt said...

evlPanda said...

Reflex Films and Gestalt (where you been?) have it.

http://www.physclips.unsw.edu.au/jw/sailing.html

i must admit i googled researched this one.

been having babies.

Aah, good. One day we can race them.

(edit: they may already have raced on little buggies)