True Wind without speed transducer

[tanglewood]

Regardless of which you find more useful, True wind is sea surface referenced, where ground wind is ground (or lat/lon) referenced.


Without speed and course through water, you can't calculate true wind from apparent wind. And likewise, without COG and SOG you can't calculate ground wind.


That said, I wouldn't be at all surprised if devices confuse the two, or calculate with whatever they can get their hands on, call it whatever you want to name it, and deem it good enough. After all, the two are usually pretty close to the same... except when they aren't.

[StoneCrab]

I have this straw hat which is pretty frayed. It tells me how strong the wind is and where it is coming from. If it blows off my head, it is really windy!

[CarinaPDX]

I find it a bit odd that the OP wants true wind but not speed through water. As others have noted, one sails to apparent wind and this can be ascertained by a masthead wind indicator (illuminated by the masthead tri-color). While I am considering buying a masthead weather sensor the next time the mast comes down, I never felt I needed it during many years of cruising. STW is a bit useful as it eliminates leeway as an effect and tells how well the boat is moving through the water. TBH my paddlewheel was jammed more often than not and I found SOG to be adequate. Racing is another matter entirely, and for that AW, TW, STW, SOG, COG, heading, and calculated leeway are required to be competitive in many situations. But for cruising this stuff is "nice to have", not essential.

Greg

[Oceanride007]

Wish there was a switch, my log speed is crap, it changes too much with tack because of turbulance around keel. For that matter my Heading is out because of Deviation in a steel hull.
(Neither of these matter a great deal, but was trying to make Polar diagram, using NavmonPC)

My instruments are Ray. The way I recall, True wind has a particular meaning that needs accurate speed and heading, the difference to Ground wind is due to current & leeway.

[mjgill1]

I have a similar set up on a Seaward 32RK. Axiom 9 RV, new autopilot and the I60 wind with anemometer on the mast. I just finished the install and in my case, after much phone time with tech support, there is no way to get TWS without an added or different transducer. Too expensive to justify. If we were long distance cruisers, maybe, but for S. FL, the Bahamas and our lake, we'll be just fine.

[The Perfessor]

Thanks for all the input. To answer a couple of the questions posed; I consider myself still a novice though I've been sailing about 10 years recreationally. I don't race. The reason I like true wind is that forecasts for wind is, based on what I've learned here, "ground wind". It helps me to to get a feel for some reliability of forecasts, and to give me some indication as to what may lie ahead. But given my apparent wind can really change based on my heading, I struggle to know if the forecast is correct and this situation is what I can expect next time a similar forecast is made. I guess I'm trying to make the connection from what the forecast wind is, to what I'm seeing, to what the conditions feel like.

To another members point, the speed over water is useful to help me understand currents. Sailing back from Cuba I was doing 9kts SOG, but I didn't know how much of that was current other than an educated guess. So SOW would certainly be helpful.

Also, a minor point, when I complete my log, I record true wind direction and speed as it seems less subject to variation in heading. Though, now I'm questioning that!

Last, it really is a nice to have, not a need to have, as another member pointed out.

I always learn a lot from you people! Thanks!

[sailjumanji]

You need speed thru the water to calculate true wind. Speed thru water is also good for ascertaining current. We are racers and cruisers, and I find speed thru water and true wind beneficial in both situations. You cant get speed thru water without a paddlewheel or some high-end transducer.

[StuM]

Originally Posted by tanglewood

Without speed and course through water, you can't calculate true wind from apparent wind. And likewise, without COG and SOG you can't calculate ground wind.

You don't need course to determine TWS and TWA. Just AWS,AWA and STW.


(Obviously you do need it to determine Ground Wind Speed and Direction.)

[sailorphil9]

Originally Posted by StuM

Knowing TWS and TWA is useful when you are planning a course change especially when going from a downwind to an upwind heading.

+1 to that


If you don't know the TWD/TWS it's difficult to relate what you're experiencing to what the forecast says. That's important to me ocean sailing.

[noelex 77]

Originally Posted by sailorphil9

If you don't know the TWD/TWS it's difficult to relate what you're experiencing to what the forecast says. That's important to me ocean sailing.

Ground wind rather than true wind is better for that application, although if the current is low then true wind will be close enough.

This is one reason I prefer a display of ground wind.

[barnab]

We have 60 series instruments and at some time a PO decided to eliminate the speed transducer. I was annoyed by having to calculate true wind all the time (and I feel it's really asking too much when sailing with an inexperienced crew).



The way to get a true wind reading is not necessarily to have a speed transducer. The instrument requires a VHW NMEA sentence (Velocity and Heading through Water). So if you can inject this information you'll get true wind without speed transducer.


If this is less work/cheaper is another question...We had a NMEA to WiFi dongle (from YachtDevices) anyway and a Raspberry Pi so I programmed it to relabel a VTG sentence (speed and course over ground) as VHW and ever since we have a true wind display. I know VHW and VTG are not the same, but I'm totally happy with the setup.

[GILow]

Originally Posted by meirriba

It will show TWS ONLY if you have speed through water transducer. If you dont, toggling to TRUE will show APPARENT data...

I'm not sure that's right. My ST60 + uses the SOG reading.

I know this, because more than half the time my water transducer is not working due to the large amounts of seagrass we have floating around here.

It's very rare for my water speed to read anything other than zero. And yet the true/apparent mode always works.

Maybe it's a 60 PLUS feature?

Edit: Or maybe it's a terminology thing? Reading here, it seems my ST60+ may be giving apparent vs GROUND wind, though it labels it apparent vs true.

Edit again: Maybe it is right... I am now less sure. My ST60+ has both sources available to it, perhaps it chooses SOG if the transducer is snagged and reading zero at the time?

Edit yet again: Now I am really confused. This article (https://forum.raymarine.com/showthread.php?tid=98) on the raymarine web site does support your statement. They say it needs the paddle wheel, but I am (reasonably) sure mine works even when the wheel is jammed. I shall have to go for a sail and check.

[noelex 77]

Originally Posted by GILow

I'm not sure that's right. My ST60 + uses the SOG reading.

I know this, because more than half the time my water transducer is not working due to the large amounts of seagrass we have floating around here.

It's very rare for my water speed to read anything other than zero. And yet the true/apparent mode always works.

If the paddlewheel is fouled, the true wind reading will still display a “true wind” speed and direction, but the result will be inaccurate. Likewise if the paddlewheel is poorly calibrated, or reads differently on port and starboard tacks. If the paddlewheel is completely jammed, the displayed true and apparent wind will be the same.

Is the “true wind” display accurate?

If you have accurate “true wind” despite a jammed paddlewheel (with some STW) , this must indeed really be “ground wind” and you have a solution to the OP’s problem. What other equipment is connected and did you select “ground wind” or “use “GPS data for true wind” in any of the menu options?

[GILow]

Originally Posted by noelex 77

If the paddlewheel is fouled, the true wind reading will still display a “true wind” speed and direction, but the result will be inaccurate. Likewise if the paddlewheel is poorly calibrated, or reads differently on port and starboard tacks. If the paddlewheel is completely jammed, the displayed true and apparent wind will be the same.

Is the “true wind” display accurate?

If you have accurate “true wind” despite a jammed paddlewheel (with some STW) , this must indeed really be “ground wind” and you have a solution to the OP’s problem. What other equipment is connected and did you select “ground wind” or “use “GPS data for true wind” in any of the menu options?

To be honest, I really don't know for sure now.

The paddle wheel is reasonably accurate from about four knots and greater, below that, it's pretty hopeless.

It's binary though. It is either working ok or completely jammed, thanks, as mentioned, to the seagrass that floats around here. Something about seagrass strands and the shape of my boat seems to force the little buggers down to the considerable depth of the sensor.

Anyway, I'll go for a sail ASAP and pay closer attention to what is happening. I rarely use the true wind speed function, it's usually just to confirm my estimates before tacking or making a sail change.

Either way, I'm no help to the OP.

[CarinaPDX]

Paddlewheel transducers can have significant errors as a result of mounting location. Newer "smart" speed transducers from Airmar can be calibrated over multiple speed ranges. It does require an MFD that can send the calibration sentences to the transducer. It might be possible to do this with PC-based software through a USB-N2K interface, IDK. The smart depth transducers can similarly have the keel offset programmed into the transducer, so that the data on the N2K bus is already corrected for all displays.

Greg