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Board » General Discussion » Sailing TWA vs Compass Course in backing wind

Posted by
Chappo


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2009-04-17 12:00:35
2009-08-11 01:36:37 - Sailing TWA vs Compass Course in backing wind
I would expect the expert IT and yachting technos know the answer and I believe the answer is linked to the polar performance but presuming the polar shows a steady increase in speed as TWA increased. I am interested to know that if you are sailing at say 50 deg TWA and sail into a backing wind, is it quicker to reach a point to sail TWA and then adjust to say 45 TWA to reach the point or to sail in compass increments of 50,49,48,47,46,45 TWA.
Posted by
NZL_PaulR


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2008-07-22 12:21:30
2009-08-11 01:54:28 - Re: Sailing TWA vs Compass Course in backing wind
A definate maybe, becoming a perhaps and possibly developing into "most Likely".

It depends upon the speed of wind change vs the performance drop from large course changes vs the hours available for SOL.

In my case, because SOL is my home page, I can check often, perhaps too often, but then again, when I sleep, I go aground, also far too often!

Look at your VMG when changing courses.

Sailing a cc is necessary if winds are changing and freeing for your current tack because speed is generally improving.

If winds are heading, the same TWA will main tain a speed, but your course will swing.

TIP: It can be a good idea when on a CC course to use the "wheel" and overlay your existing course but then set the TWA.
Now your predicted course will ben "bent", sometimes helpfully, but according to Plato's Rule, 80% of the time it will bend the wrong way.

Forrest Grump said "Shit Happens!"

. . . and then there is sailing

My $0.02c worth
If it breaks, it's not strong enough!
Posted by
Chappo


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2009-04-17 12:00:35
2009-08-11 02:30:30 - Re: Sailing TWA vs Compass Course in backing wind
Thanks Paul, that was more like $5 worth. As you say the VMG is also quite relevant although it changes in slow increments unlike the boat speed which moves quickly. I am also curious when setting a best VMG when working, for the the same VMG number do you choose the highest BS setting, the lowest BS setting (to get best VMG hidden decimal places!!??) or go for a middle setting. I find the middle setting seems best.

What yacht are you helming?

Peter (Chappo)
Posted by
NZL_PaulR


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2008-07-22 12:21:30
2009-08-11 02:41:59 - Re: Sailing TWA vs Compass Course in backing wind
Middle = Highest VMG and hopefully the distribution graph is not skewed too much.

NZL_PaulR
If it breaks, it's not strong enough!
Posted by
Chappo


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2009-04-17 12:00:35
2009-08-11 02:57:30 - Re: Sailing TWA vs Compass Course in backing wind
Thanks for VMG confirmation.

Ahh a Kiwi. I was born in Greymouth (well described as the least pretty town in NZ) but left in a flying boat when old enough to fly at 6 weeks so now officially an Aussie. Been back a few times for skiing, yachting, gliding at Omarama.

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