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post #21 of 67 Old 02-16-2011
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I get it...this is an example of FUZZY LOGIC.

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post #22 of 67 Old 02-16-2011 Thread Starter
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Fuzzy Logic indeed...... I should never have edited my original post. My goof, wind is from astern , current is flowing in same direction as wind.

So edit is incorrect (well it was until I went back and fixed it ) finishing line is downwind when viewed from the boat with ten knots from astern.

Now stop trying to confuse me will you ? This is supposed to confuse you lot not me. I already knew the answer.

Andrew B

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post #23 of 67 Old 02-16-2011
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Quote:
Originally Posted by tdw View Post
Boats A and B are identical and sailed by equally skilled crew.

Both are same distance from finish line.

Both are in a ten knot current flowing in the same direction as the boats.

Boat A has ten knot true wind from astern, Boat B no wind.

What will be the result ? A B Tie

Why ?

(To be completely clear both boats are directly downwind from the finishing line. Current is also running in same direction as wind.)
If both boats are downwind of the finish line, and the current is identical, both boats are moving away from the finish line. However, boat "B" has no wind behind it, therefore, it is moving into 10 knots of wind created by it's forward motion, thus it is moving slightly slower than boat "A", which has no apparent headwind because it has been nullified by the 10-knot wind coming from astern, thereby allowing it to move forward with less resistance.

It's Margaretta Time!

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post #24 of 67 Old 02-16-2011
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Each boat will win its respective race.

They are sailing in different races - this explains how one boat has wind astern and the other has no wind.

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post #25 of 67 Old 02-16-2011
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I'm casting my vote in favor of B.

Boat A has no choice but to drift with the current. If she somehow manages to alter course and make headway in any direction at all, her apparent wind will always be dead ahead, and so she can never sail.

Boat B can alter course to close-hauled. Let's pretend the finish line is infinite long and forget about Boat B's tacks. Boat B will now make, say, 5 knots over water on her heading 45 degrees away from the set of the current, which is 3.5 knots made good in addition to the current, or 13.5 knots made good toward the finish line. She will experience some leeway, but its component in the upstream direction should be less than her additional 3.5 knots. This beat's A's 10 knots, so B wins.

I don't see how this situation is substantially different from two boats in a sea with zero current, and one (B) has ten knots of wind blowing from the finish line, whereas the other (A) has no wind. There may be some wind-against-tide action affecting B, making her tacks take slightly longer (that's one of the reasons I'm imagining an infinite finish line), but as long as she can average any speed at all upwind, she wins.

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post #26 of 67 Old 02-16-2011
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The plane will take off. The wheels are only turning because of the treadmill...

Oh - Wait.
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post #27 of 67 Old 02-17-2011
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Here is my original PM to Andrew

Quote:
We usually use the term apparent wind as meaning boat speed +/- wind. On a run / broad reach apparent wind would less than true wind. On a beam reach to close hauled apparent wind speed would be higher that true wind speed. In all cases the wind angle would shift forward.

With current, if the boat is moving at the speed as the current the current speed would negate the wind (Boat A). They would get no wind to fill sails so I could not see them generating any speed through the water. Their SOG / SMG would be 10 knots. In the case of boat B, apparent wind would be on the bow and equal to the wind on a run. Friction through the air would slow boat B slightly. They would have a slight negative sped through the water, but a positive SOG / SMG less than that of boat A.

Boat A should finish first.
Another consideration.

Even if Boat B gets 10 knot apparent, they will will lucky to get a 45 degree wind angle. They will have to sail 40% farther than Boat A.

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post #28 of 67 Old 02-17-2011
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(To be completely clear both boats are directly downwind from the finishing line. Current is also running in same direction as wind.)

Now you've gone and done it.
If they are directly DOWNWIND (that means wind blowing FROM the finish line) ... AND boat A has the TRUE wind ASTERN; THEN, Boat A is obviously NOT headed towards the finish line but away from it ... and will on the present course need to travel approximately 22,000+ miles or the entire circumference of the earth to cross the finish line. Since Boat B has NO wind and only current, then boat B will take twice as long of WHATEVER it takes A to go that 22000 nMi distance.

In this case A 'wins'.
;-)
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post #29 of 67 Old 02-17-2011 Thread Starter
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Go back and have a look at the original post in its edited form

Wind is blowing towards the finishing line. Current is flowing towards the finishing line.

So Boat A has ten knots of true wind from astern and ten knots of current towards the finish.

Boat B has ten knots of current towards the finish. Zero wind.

Andrew B

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post #30 of 67 Old 02-17-2011
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This is supposed to confuse you lot not me. I already knew the answer.
Or thought you did
Strange weather over there.
Unless one of the boats is anchored
Safe sailing

The great appear great because you are on your knees. James Larkin, Irish Labour Movement.

Last edited by centaursailor; 02-17-2011 at 01:38 AM.
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