I have a WS310 wind sensor at the top of the mast. It displays wind angle and speed. To get True Wind Direction, I think I also need a heading sensor, maybe the Garmin as it's the least expensive and I don't need it to be insanely accurate, +/- 3 degrees as specced is ok....what other sensor do I need for TWD to calculate and plot wind shifts for the purpose of racing tactics? Thank you!
Sensors Needed for obtaining TWD so I can display wind shifts on B&G Vulcan 9.
- Thread starter justin.hendo
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I think there should be a pair of settings to use Speed Over Ground and Course Over Ground for true wind calculations. At least on the Zeus series those settings are available. By using those you should be able to get TWS and TWD calculated with just the wind sensor and GPS course/speed.
Are you doing the calculations by hand, or will your existing instrumentation take care of it once it has the proper inputs? I think GPS speed and heading should be all you need.
Edit: Oops, typed too slow.
Edit: Oops, typed too slow.
I'll look into the settings, I find the Vulcan user manual to not be very detailed in the setup and the millions of options available...
That would be nice to use COG to derive TWD. Otherwise, I'll have to buy a $150+ heading sensor and run that into the NMEA2k network.
I don't intend to do the calculations by hand as I sometimes short hand the boat and want the system to show me the Median and Current wind plot as shown below so that I can predict what phase the wind is in. This is a screenshot from the interwebs. My advanced wind plot doesn't show any data because TWD is blank.
That would be nice to use COG to derive TWD. Otherwise, I'll have to buy a $150+ heading sensor and run that into the NMEA2k network.
I don't intend to do the calculations by hand as I sometimes short hand the boat and want the system to show me the Median and Current wind plot as shown below so that I can predict what phase the wind is in. This is a screenshot from the interwebs. My advanced wind plot doesn't show any data because TWD is blank.
I may be a bit confused, but I think you need only boat speed and apparent wind direction to get true wind direction; but I'm not sure B&G allow this with GPS SOG.
Heading is necessary for radar/chart overlays, though, so if it's in the budget I highly recommend it.
Heading is necessary for radar/chart overlays, though, so if it's in the budget I highly recommend it.
You can get true wind angle (relative to the boat) with just boat speed and apparent wind speed and direction. To get true wind direction (direction of the wind over the earth) you need the boat’s heading or course. The time plot that the OP is showing is for wind direction, not angle, so you do need the boat course or heading.
Technically speaking, if there is current then the wind speed and direction over ground does not match wind speed and direction over water. Using Speed Through Water and Heading gives you the true wind over the water (plus or minus leeway, which the computer may or may not compensate for). Using SOG and COG gives you true wind over the ground. B&G defaults to wind over water, as that’s what racers care about, but should be able to be switched to ground-referenced, as they do on the Zeus series.
...which you can get from the compass.
My TWD shows true wind relative to my heading.I don't think that's correct in the case of a current. Course and heading will not be the same.
B&G differentiates between “true wind direction” and “true wind angle”. Direction is the actual magnetic direction of the wind relative to earth. Angle is relative to the boat’s bow. See this from the Zeus manual for example -...which you can get from the compass.
They call out TWA in their explanation of the graphic, but you can also see TWA and TWD listed separately in data boxes on the left of the screen. The plot that the OP is referring to uses TWD.
Concur that in the case of current COG will not match heading. Using heading for the calculation gives wind relative to the water. Using COG gives wind relative to the ground.
Here’s an example - Say there is a river flowing to the south at 4 knots. The wind is blowing over the earth from north at 2 knots. Say you motor directly into the current at 3 knots through the water, which means you’re actually going backwards at 1 knot over ground. Your heading is 0 degrees. Your COG is 180 degrees. Your apparent wind is 1 knot on your bow.
You calculate true wind over the ground by adding the apparent wind speed vector to the boat speed and course over ground. Those vectors total to 2 knots from the north, which is correct.
You calculate true wind over water by adding the apparent wind speed vector to the boat speed through water and heading. That’s 1 knot from the north plus 3 knots from the south, which nets 2 knots from the south. That accurately represents the wind speed over the flowing water.
Sounds like I need at least one more sensor to make my dreams of laylines and wind shifts to be graphically displayed on the Chart Plotter.
Update, I called B&G and technical support said I need the following for this to work....another $800 worth of transducers and won't be possible until I haul out in the fall
Depth, Speed, Temperature Triducer (B&G) -$400
GPS Antenna w/ Compass (B&G) -$300
These things being NMEA2k I'm thinking I can find Similar or good enough sensors...I don't need Gucci Gear for this, I'm in a pearson 26 that has more money in electronics than the rest of the boat and sail inventory is worth and I don't want to tip the scales too much further in that direction to be honest.
Garmin Speed Sensor - $160
Garmin Heading Sensor -$140...$300 bucks total for the same data... am I crazy? I have an existing depth transducer that reads on a dedicated display, I don't really need another depth sounder on the hull...
Update, I called B&G and technical support said I need the following for this to work....another $800 worth of transducers and won't be possible until I haul out in the fall
Depth, Speed, Temperature Triducer (B&G) -$400
GPS Antenna w/ Compass (B&G) -$300
These things being NMEA2k I'm thinking I can find Similar or good enough sensors...I don't need Gucci Gear for this, I'm in a pearson 26 that has more money in electronics than the rest of the boat and sail inventory is worth and I don't want to tip the scales too much further in that direction to be honest.
Garmin Speed Sensor - $160
Garmin Heading Sensor -$140...$300 bucks total for the same data... am I crazy? I have an existing depth transducer that reads on a dedicated display, I don't really need another depth sounder on the hull...
Note that B&G, Simrad, and Lowrance are all the same stuff, with different price points and features in the MFD's. Lowrance sensors are marginally less expensive than B&G.
It’s sad that the Vulcan can’t do the calculations with just the SOG and COG the way the Zeus can. I’d still look for those settings in the menu. I wouldn’t be surprised if the functions were there and the tech just didn’t think about it that way.
My guess is that the Garmin heading sensor would work. Does the Garmin speed sensor report speed over ground or speed through the water? If the B&G tech is right you’ll need something that reports the speed through water sentence, not just speed over ground.
The other advantage of sticking with the B&G recommended gear is that if/when it doesn’t work you have more recourse with B&G. If you mix the Garmin equipment in B&G will happily point fingers at them for any incompatibility.
My guess is that the Garmin heading sensor would work. Does the Garmin speed sensor report speed over ground or speed through the water? If the B&G tech is right you’ll need something that reports the speed through water sentence, not just speed over ground.
The other advantage of sticking with the B&G recommended gear is that if/when it doesn’t work you have more recourse with B&G. If you mix the Garmin equipment in B&G will happily point fingers at them for any incompatibility.
There is another option too, but it’s quite a bit more DIY. You could put a Raspberry Pi in the boat with an NMEA 2K adapter. The Pi could do the calculations and inject TWD onto the network. (I assume that if the TWD were being provided over NMEA the Vulcan could plot that, but I’m not 100% sure.). Worst case the Pi could just read the SOG and COG and echo them back on the network as speed through water and heading for the Vulcan. Pi’s are really hard to find right now, but if you could find one the total cost of parts would probably be similar to the Garmin option. And once you have a Pi on board it opens up options for more cool things like logging and monitoring.
Justin, I agree with you regarding the cost of these components.
I once pined for all this information but when I finally got some of it - it turned out to not be as great as I hoped. For one thing the boat speed is, at best, inaccurate. The paddle wheel becomes fouled and unless you clean it before every race it will be hard to get repeatable results. And you can set your boat speed to a knot or more of your speed thru calibration. I know the B&G software is very powerful but you can do without it. Preparation of the boat and buying good sails will yield better results.
There is also the phenomenon of "Getting your head out of the boat." I firmly believe that fledging racing sailors need to look away from their instruments and keep their minds on what's happening on the race course. If you are steering you will feel lifts and headers on the tiller. You will see them on the tell tails. More over you should look at the boats ahead to determine what the wind is doing. It is developing those skills that will improve results. More time sailing your boat will get you there.
I once pined for all this information but when I finally got some of it - it turned out to not be as great as I hoped. For one thing the boat speed is, at best, inaccurate. The paddle wheel becomes fouled and unless you clean it before every race it will be hard to get repeatable results. And you can set your boat speed to a knot or more of your speed thru calibration. I know the B&G software is very powerful but you can do without it. Preparation of the boat and buying good sails will yield better results.
There is also the phenomenon of "Getting your head out of the boat." I firmly believe that fledging racing sailors need to look away from their instruments and keep their minds on what's happening on the race course. If you are steering you will feel lifts and headers on the tiller. You will see them on the tell tails. More over you should look at the boats ahead to determine what the wind is doing. It is developing those skills that will improve results. More time sailing your boat will get you there.
I would like to do this, I'm an automation integration engineer, so it's up my alley. I wasn't aware pi's are hard to find, I'll keep that In mind.
The Garmin speed sensor reports speed through water. The thing that I hesitate with buying more expensive paddle wheel sensors is, I think they're all made in the same place, and they all report over the same standard addressing via NMEA2k I believe. I get that the speed through the water is needed for live current data, but like you said it should be able to approximate it w/ COG and give me fairly accurate TWD data.
Thank you for this. I agree, I get my head in the boat quite a bit, sailing to VMG sometimes instead of using tell tales that are telling me I'm pinching. I find it hard to resist pointing up to 30-32 degrees apparent and watching the VMG number climb climb climb...(note, I'm in a Pearson 26, the 30 degrees is way high for me I believe....maybe if my sails are trimmed perfectly with the deepest draft forward a bit)
I've recently invested in stripping and fairing the keel, I put burnishable hard ablative bottom paint on her, and a new 155% G1 sail from Fries Sail Design. I might go for a #3 sail but other than that I'm feeling fairly good about the sail inventory.
I do think I'm trying to make up for my lack of sailing knowledge as far as sensing headers and lifts goes, with my engineering ability...I do need to learn to sense the puffs, lifts, headers, you name it....and spend more time on the course head into the wind to try to time the wind phase shifts...that's the real goal for me...I'm trying to play the conservative game of sailing to lay line percentages and tacking only when an advantageous wind phase is present or another good tactical reason to tack.
Sometimes I put the covers on the wind/speed/depth gauges and turn off the MFD and just sail the boat by the wind on my face and the wheel in my hand....
I'm sure its possible, but couldn't you get heading from the fancy 6 axis accelerometer that is in your smartphone?
It has the right data, but I don’t know any way to put it on the NMEA network. MFD’s often provide NMEA0183 streams via Ethernet or wifi for devices like phones and tablets to consume, but I don’t think they accept incoming data except via NMEA2K input.
Unfortunately for a pretty significant markup. The resellers buy up any available stock and resell it on Amazon for close to $200. MSRP is $35-$50 depending on model.