True Wind Speed and Direction - Page 2 - SailNet Community
Old 11-28-2008
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Jim,

the ST60 is NOT to be used to tell you where, as in which magnetic direction, the wind is coming from..it's used to tell you, in relatiion to your bow, where is the true/apparent wind and how strong they are...

It's a sail realted instrument, not a navigation instrument.
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Old 11-28-2008
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Just be aware that it will only give you an approximate true wind and direction. The reason I say this is that the ST60 wind instruments, like those of most brands, will use the boat's speed through the water (STW) for the calculation, and the speed through the water may or may not be accurate, since the speed transducer can be affected by things like current. It would far more accurate for the wind instrument to use GPS derived SOG and heading.

For instance:

Say the boat is sailing a course of 0˚ at 10 knots, and the true wind is 10 knots at from the east @ 90˚. If there is no current affecting the knotmeter—the knotmeter shows a speed of 10 knots, and the apparent wind will be 14.14 knots at 45˚. The wind speed indicator will calculate a true wind of 10 knots @ 90˚—which is the true wind speed in this case.

However, if the boat is moving at 10 knots with a heading of 0˚, with a five knot northerly current—the knot meter will only show a speed of FIVE knots. The boat is still moving at 10 knots SPEED OVER GROUND, the apparent wind will still be 14.1 knots at 45˚... but will calculate the true wind to be 11.14 knots at 63.5˚, which is wrong.

Sailingdog

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Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 11-28-2008
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I'm not aware of any instrument sets that use SOG to calulate true wind. is anyone?
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SD, thanks for the caution, but I understand the effect of current and the difference between hull speed and speed over ground. In the places we'd use the device, current would be mostly a non-issue, because there's not much current, if any. Most times our speed log and GPS SOG agree with one another to within one or two tenths of a knot, if not right on. (Other than when we're under motor in rivers or canals, where there are currents.)

Jim
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Old 11-28-2008
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I wonder how it copes with leeway? If I am side-slipping, how does it know? I trust it makes an allowance for that too?

The boat never really sails the way it is heading. It could be compensated for, I suppose.
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Old 11-28-2008
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This subject piss me off .....

Jim,

we had this discussion some time ago ( I fully disagree to Raymarine ..... ). And still in the same position. Raymarine requires the wrong SOW information (Speed Over Water provided by that damm dirty paddle that goes into log inst.) to calculate TRUE wind. This is an aberration from an engineering stand point, as the only info rasonably accurate for TRUE (any true) calculation is SOG (Speed Over Ground) which any ordinary GPS can provide with far good accuracy. Although Raymarine agree with that, they insist in to use SOW, instead. OK, they could use both (precedence to SOG of course), but seems this is the only way to force users to BUY the damm log. I still love Raymarine technology, but every time I go through this I get pissed !!!!

Nave Rara
Beneteau Oceanis 43
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Old 11-28-2008
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I'm unclear; can the ray st be used with gps only or not?
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Old 11-28-2008
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look guys..I don't think I understand why this is deacying like this..there is even a guy with a blood clog about to burst over this...

It is nothing more than a sailing aid...NOT a navigational instrument...

It's better than nothing....it is what it is..I've been using them for decades....

besides..I use tell tales and the windex...both are apparent wind indicators...

True wind is to prove if the BFS merda de boi is true or not...

Who the hell sails on true anyway???
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Old 11-28-2008
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Nope... doesn't account for leeway at all. If your boat is side slipping that much, you're probably doing something wrong.
Quote:
Originally Posted by Rockter View Post
I wonder how it copes with leeway? If I am side-slipping, how does it know? I trust it makes an allowance for that too?

The boat never really sails the way it is heading. It could be compensated for, I suppose.

Sailingdog

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Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 11-28-2008
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Giu,

I'm don't know if you take merda de boi at any price. Despite refusing daily offers, here, we try like hell don't pay for it! It is the principle/concept behind, not the fact itself. 'Cmon .... we're not discussing if boating is essential to living or not ....

Xort, No, it doesn't work !! If you have Raymarine, the only way to display the "almost true" wind is to install the ST speed.

Nave Rara
Beneteau Oceanis 43
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negrini is offline

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