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Discussion Starter · #1 ·
I contacted Raymarine support many times, but couldn't get a good answer. So, although I'm still a good Ray's customer, I'd like to share this. Raymarine's wind instrument shows TRUE wind only if you have speed over water information (i.e from the "paddle thing" installed). I refuse to make another hole to get wrong measurement anyway, and argue that TRUE wind could be calculated correctly only using SOG (speed over ground). Raymarine gave me several explanations (foolish ones) and I believe the only reason for that is to PUSH the market to purchase that "paddle thing". In critical situations (downwind with a spi, for instance), the wrong information could lead to wrong decisions and threaten your safety. Have you ever considered that ?
 

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Then get one of the paddle thingy's that mount on the transom.

And, if you want to derive true wind, you're going to have to make a determination of vessel speed somehow; by estimate or empirical input. But then, as the Rock says, who cares what true wind is?
 

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Negrini-

You can get a triducer, which gives you the speed, depth and temperature in a single unit. It requires a slightly larger through-hull than your current depth transducer, but would solve the problem.
 

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negrini

Welcome to sailnet. I'm going to disagree with you on this. Current and set will affect the truewind reading which is why you need SOW. Of course if your sailing on a lake or non-tidal area, that's different.
 

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Speed through the water is an unnecessary and potentially misleading input when calculating true wind speed, just as Negrini is arguing.

Take this example: You're entering the San Francisco Bay with a true following wind of 20 knots. Your boat speed though the water, as derived by a paddle-wheel, is 5 knots. You have a flood current of 5 knots behind you. The apparent wind reading is 10 knots (20 knots minus 5 knots boat speed minus 5 knots current speed).

If you're just reading boat speed through the water, you'd conclude -- incorrectly -- that the true wind speed was 15 knots (10 knots apparent wind plus 5 knots boat speed).

The only way to calculate true wind speed is to know the speed of the boat over ground (SOG) and the true course over ground (COG), and to reconcile this with the apparent wind speed and direction. SOG could be derived from, e.g., a GPS input but certainly not from a paddle-wheel device.

And, yes, in a lake or low-current situation it wouldn't matter much.

And, yes, if the helmsman had both GPS speed info and apparent wind info he/she could calculate true wind speed easily enough. I was in just such a situation last week, when singlehanding with a following wind of up to 28 knots true and a following current of just over a knot. Example: with an apparent wind speed of 18 knots behind me, and a GPS-derived speed over ground of 8.5 knots (including an estimated following current of 1 knot), I could easily estimate the true wind: 18 knots apparent plus 8.5 knots COG = 26.5 knots true.

Why did I care about true wind speed? Easy. Because I was alone, sailing in relatively restricted waters, having to make significant course changes which involved gybing. Jibing a full main on a 40+ foot vessel in 26 knots of wind is no fun, and must be done very carefully if you're not going to break something. So it was very important to me to know that although my apparent wind was, e.g., only 18 knots, the true wind speed was over 26 knots.

Bill
 

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Discussion Starter · #7 ·
Breezing, let me beter clarify

Regardless the current, TRUE wind is a measure of speed over ground, not over water !! Suppose you're sailing dead downwind at 6knots against a counter-current of 6knots: your wind instrument will show you ZERO true wind, but reality is, since your are still relative to the ground (SOG is zero in this example), the reading should be the real 6knots of wind. So, your Raymarine instrument will fool you exactly by the current. And for the others not caring about this, I always read the instrument to decide for a spi, and as a single handed, I push my engine along with wind to create a 1-2 knots apparent. This makes setting the spi a breeze, and once I'm done, I just kill the engine and the spi fills; very safe right ? Unless you use Raymarine instrument. Since GPS is a commodity for boats nowadays, SOG is plenty available over the cables. Why simply Raymarine doesn't take SOG instead of SOW for true wind calculation ?
 

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Good points from both of you. I guess I was meaning to say Raymarine uses both in order to get an instrument reading of accurate truewind. That SOG won't do it independently which is how I read the original Post. I'm not disagreeing with you. I'm just saying that for the Instrument to display an accurate Truewind, it does the math so you don't have to.
 

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I find it easier just to have a masthead wind speed indicator and to do the math in my head. The sea state tells me in most cases the true wind speed if I'm on a run holding a candle in my hand (grin). Frequently, I have been on a broach reach in rolly stuff doing six or seven knots cool as a cucumber...and then I see some similar boat rail down, bone in her teeth, beating toward us with the occasional bucket of green chucked back to the cockpit... That's when I think..."ah, best roll in the jib and lose a knot before we have to make that turn...dear, would you fetch me my foulies?"
 

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Brezzin-

The "TRUE" wind reading on Raymarine instruments is only an estimate... it really isn't ACCURATE IMHO, since a current could easily throw it off.
 

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None that I know of yet... Maretron might be, but I'm not sure...
 

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Discussion Starter · #14 ·
Well, I agree to you that good sense is ....

unvaluable, and many has developed a 6th sense to that. I red people heading navigation based on wave shape, I personally saw an experienced sailor finding our way through a foggy afternoon just looking to the dirt milky water to find a channel entrance. But, if you often navigate in unknown grounds, that could pose some threat (minimized by your long run experience). Waves shape, sea state, wind gusts, etc .. are all dependent on the environmental conditions (sea bed, coast profile, latitude, pressure, etc ...) and your location IS the major condition. So, getting used to a familiar ground save a lot (I barely turn on my E80 on a typical day sailing). Aftermost, Raymarine drive me nuts by not recognizing their mistake (unforgivable) and my only explanation is to force you buy that #$$%##@ "paddle thing" !!
 

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Negrini, I think you are forgetting that the simplest answer is usually the most likely one.

Simple, as in, these instrument systems and processes have been in place way before GPS was available, or even LORAN. And the first and most basic instrument on any boat is usually the paddlewheel speed log.

There's no great conspiracy to force you to buy anything, they are simply calculating true wind (or what they consider true wind) by the same means they have done so for the past 30? 40? years. Which is by taking a wind sensor and adding it to the paddlewheel that already was installed on almost every boat interested in any kind of instrumentation.

Old, simple, crude, lazy, incorrect, might all spring to mind. But forcing you to buy more of anything? I don't think so. Raymarine only "forces" you to use their rayspeak-gear for everything, rather than making everything work with NMEA. That's enough "forcing". (Either you buy their gear, or their converter boxes, either way, that's proprietary enough to be a stopper for some boats.)

Now, instead of trying to make Raymarine change their ways, why not find some sailors who have computer skills, and let them set up a freeware program that runs on cheap laptops, integrating universal masthead wind sensors and GPSes to produce real true wind and other data? You could cut Raymarine out of the picture entirely that way, it should be a simple (ha) exercise.

Of course without the paddle thingy, you may know SOG but you'll never know what currents you are in. I'd call a boat without a knotmeter "hopelessly impaired" for racing navigation, no matter how good the GPS was.
 

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Had the same argument with Raymarine tech people at the Annapolis show a few years ago. Same crappy excuses. The SOG is on the data bus but would require a firmware upgrade to use it in the calculation of true wind speed and angle and they had no interest in the upgrade.
 

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Had the same argument with Raymarine tech people at the Annapolis show a few years ago. Same crappy excuses. The SOG is on the data bus but would require a firmware upgrade to use it in the calculation of true wind speed and angle and they had no interest in the upgrade.
I bet this is a trivial fix that someone could even do on their own. It would likely literally require searching the firmware binary and replacing STW with SOG. I think the format of data is the same, so that would be the only thing.
 

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Discussion Starter · #20 ·
Thanks Hello ! This reminds me how good sense can drive us back to the rails. You're right, and I don't wanna make this a battle horse. I'm an old "lab rat" computer engineer, and should have avoided such trap a long ago. Brack, your search is correct STW and SOG have the same NMEA sentence format, and once you have a SeaTalk bridge, you can easily translate into whatever you want. My boat has 4 parallel nets for reliability (NMEA, SeaTalk, HSBus and Wireless) and using my StandardHorizon Plotter, I think I could bridge it. When spoke to Ray's engineer, I suggested to look first at SOG sentence, then STW, but you know how they care about it. Anyway, I like the idea to dump the firmware and change the setence match, that would be interesting, fixing and very very very very fun to me ..... once I have the time and the courage to split a ST60 appart, will share with you all.
Thanks guys. As my first post, I feel this is THE forum to be in !!!
 
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