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The Admiral and I once thought we wanted a Raymarine ST60 wind speed and direction instrument. To me, though, such an instrument would be less useful than it could be without the ability to also yield true wind speed and direction. Talking to a fellow club-member a few days ago, he asserted the ST60 wind speed and direction instrument could do that. I just looked at Raymarine's site and, sure enough, it claims the instrument can do it. Curious: I downloaded the PDF of the user's manual. Yup: It says it does it. But here's the thing I don't get: Perhaps my mad math skillz are rusty, but ISTM that for the instrument to yield true wind speed and direction, it would have to know boat speed and heading. But the instructions for the device don't indicate having to hook up Seatalk connections to devices that will provide that. So how the heck can it calculate true wind speed and direction without knowing boat speed and heading? :confused:

Jim
 

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I believe that they are assuming that you have the speed log and the flux-gate compass installed already. One of my bones of contention with these companies, of particular concern in internet sales, is that it like pulling hen's teeth to get the details you need pre-purchase. Whether this stems from a history of customers purchasing primarily through a knowledgeable dealer and not direct, I do not know. But it would be hardly the first time one opened the box to find the "installation" manual only to discover facts that no one seemed to know pre-purchase.

The West Marine catalog usually has more information than the manufacturers provide within their technical articles and this case is no exception; you need velocity information, either from GPS or speed log and electronic compass.

Now as to what is compatible......
 

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SEMjim :

It can't. You are right.
The central processor must know true boat speed and true heading before it can make that correction. If there is a tide running, even boat water speed will not do it, it has to be groundspeed, so a GPS feedback is needed.
Happily, relative wind speed and direction are more important.
 

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The boat speed I understand, and that I agree if you are using speed over water you won't get an accurate reading, although if you're not in an extremely strong current you should be able to get a pretty good reading of the true wind speed.

The compass connection is not necessary if you are just looking to get a true wind direction that is in relation to your current boat heading. And if you really want to know what the compass direction of the wind is, just look at your compass and the true wind direction in relation to your boat and you should be able to get a pretty accurate reading of the compass heading of the wind.
 

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Jim


the ST60, when connected to the ST60 Tridata or ST60 speed log WILL indicate TRUE WIND speed and direction, as well as APPARENT wind and direction.

If you disconnect the seatalk cable it will only indicate apparent wind speed and direction.

Your speed log must also be calibrated correctly to allow the true wind to be calculated accurately.

The ST60 mainly measures apparent wind only and calculates true by compting boat speed..IT DOES NOT NEED a compass connected to it..

Now..if ypu are into or down a current, boat speed over ground changes, and as a consequence, the true wind direction and sopeed will change accordingly...

A current smaller than say 2 or 3 knots is not going to make a big difference.

but it does do all that..needs a speed log and a connecting cable...NO COMPASS needed
 

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My ST60 reads both apparent and true wind speed. I also have the ST60 knotmeter too. There is definably a difference in the reading, direction etc when on apparent vs true.

I do not have it hooked to a GPS, which might yield something slightly different when I am in a tide running here in puget sound, but there is a difference in what it reads as is.
Marty
 

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Discussion Starter #10
Jim


the ST60, when connected to the ST60 Tridata or ST60 speed log WILL indicate TRUE WIND speed and direction, as well as APPARENT wind and direction.
Happily, we have an ST60 speed log.

The ST60 mainly measures apparent wind only and calculates true by compting boat speed..IT DOES NOT NEED a compass connected to it..
I guess my mad math skillz are rusty, because you and CalypsoP35 are correct--something I could've determined from a trivial bit of research. For example: True and Apparent Wind Speed Calculator (sailingusa.info).

Cool :)

However: By "true wind direction," I meant as a compass heading. Wind compass heading is another thing, as CalypsoP35 noted. The ST60 device doesn't provide for that, in any event, and the necessary addition/substraction even I should be able to handle :p.

Thanks, Alex, everybody else!

Jim
 

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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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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. :)
 

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Discussion Starter #14
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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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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This subject piss me off .....

Jim,

we had this discussion some time ago ( http://www.sailnet.com/forums/gear-maintenance/41946-i-fully-disagree-raymarine.html#post294906 ). 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 !!!!:hothead :hothead :hothead
 

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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....

never had any issues...

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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Nope... doesn't account for leeway at all. If your boat is side slipping that much, you're probably doing something wrong. :)
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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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.
 
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