Ultrasonic wind sensor [CV7]

[smiagol]

Hi guys !

I want to buy the LCJ Capteurs CV7 wind ultrasonic sensor to get wind direction, speed and baro for my boat, but I'm not sure in few things and I will be very happy if some one can help me
because there is some lack of information on the website...

Does this sensor has a compass built in? how it calculates the wind angle that relative to the North? or it's relative to to my alignment point?...

The boat always in move so it's hard to understand how static wind sensor can calculate the right angle without a flux-compass inside or something similar...

[billknny]

I am confused... on the website I see that the instrument outputs the following data:

IIMWV: angle, wind speed and checksum
WIXDR: wind temperature
PLCJ: manufacturer data
PLCJE: manufacturer data

None of which require a compass, and would be typical of any mechanical wind sensor.

[hoolie]

I think it measures relative wind, just like most wind sensors. You need to calculate true wind using heading data in your MFD or computer.

If you want the wind sensor to do all the calculations you'll need to buy an Airmar 220WX or equivalent that has compass, 3-d gyro and GPS. More expensive of course!

[nauticalnomad]

Ive got one. It only seems to work through my autopilot. I need to set up the laptop program for it. I bought it as i was sick of hearing the cups falling off the Nasa ones etc. It works so far.

[smiagol]

Originally Posted by billknny

I am confused... on the website I see that the instrument outputs the following data:

IIMWV: angle, wind speed and checksum
WIXDR: wind temperature
PLCJ: manufacturer data
PLCJE: manufacturer data

None of which require a compass, and would be typical of any mechanical wind sensor.

Correct man, but the IIMWV angle is relative to what? how i'ts gettig the heading? in case its only connected to PC

[smiagol]

Originally Posted by nauticalnomad

Ive got one. It only seems to work through my autopilot. I need to set up the laptop program for it. I bought it as i was sick of hearing the cups falling off the Nasa ones etc. It works so far.

So it's getting the heading from the autopilot or from itself?
I want to connect the CV7 direct to PC and affraid that it will not get the right wind angle because the heading is missing...

[brodiej]

Smiagol, wind angle from these instruments is relative to the device itself. That is, if mounted to the top of the mast, the wind angle is AWA/Apparent Wind Angle. The wind, relative to your vessel.

To gather AWD/TWD (Apparent wind direction, True wind direction) you will indeed need a compass onboard. If your boat can interpret the IIMWV sentance and provide you TWD will require a compass, and the right sort of instruments.

The comment previously about their's working with their autopilot is very possible since it would itself have a gyro/compass for heading. If you system is all networked and all the NMEA feeds into your PC then this may still be viable.

I will however mention that youll typically find AWA of more benifit than TWD unless your a performance racer seeking shifts.

[ChrisseH]

I agree that the most common reason for being interested in TWD in sailboats is for seeking shifts during racing. Another reason could be to follow the behavior of TWD as a part of meteorological observations. The interest in barometric pressure would indicate that this perhaps is the main interest in Smiagol's case.

There are a few wind sensors with integrated compasses in the market. It is however important to acknowledge that the best place of a compass is not in the mast top and that also a built-in compass needs to be compensated for magnetic deviation and declination. Also heeling has an impact on both the compass and the wind measurement. To what degree these compensations are done automatically in these sensors I don't know. Personally I prefer to use separate sensors for the various parameters and to make the compensations and true wind calculations in the software I have in my PC.

[boatman1]

I installed the Airmar Wx 220 system in 2012, using a Furuno RD-33 for display. Brand new it performed as advertised. In fairly short order the temperature sensor failed, then one by one all gave up the ghost, with the GPS antennae last to go, which failed in 2016. Dissappointing, as the device was/is not inexpensive. Great concept, but I wouldn't buy anything similar unless the warrantee is better than the Airmar (by a shot). As a comparison, the Signet analog stuff still works after 38 years.

[Jman]

In order to get true TWA (true wind angle and TWS (true wind speed)) you need boat speed, apparent wind speed and apparent wind angle. To get TWD (true wind direction) you need to add heading. The device the OP is looking at only has apparent wind speed and apparent wind angle.

[lolly08]

3 Types of wind:

Apparent: You need a Wind transducer only.

True Wind Direction: Wind & Speed transducer (calculates speed thru the water)

Real Wind Direction or Magnetic Direction: You a Wind, Speed and Fluxgate Transducer;

The GPS can be used for Speed but the accuracy will be less.

[ronstory]

yes, I have the CV7.

It is a simple device, just wind velocity relative to the sensor (speed & direction). The MFD does the cool math to map the sensor data to true wind and place the apparent wind on the graphic and speed.

If you won't have heading sensor, the MDF (at least Raymarine) will use the COG from the GPS to calculate true wind angle. Also, I've noticed that sometimes when i'm in the slip, and the tide is right... I'll sometimes get a like a 0.1 Knot SOG from the hull sensor. that will cause the apparent the true wind angle to diverge a tiny bit.

Also, there is some hysteresis in the system for sensor's sampling rate to keep the swing effect down so it seems like true wind angle will lag behind a change in direction of the wind, even with the boat tied at the slip.

All in all, I'm happy with the CV7 accuracy and response.

[seandepagnier]

What about side slip through the water?

This seems to often be ignored, but I don't see how true wind (over water) can be calculated without it

[Jman]

Originally Posted by boat_alexandra

What about side slip through the water?

This seems to often be ignored, but I don't see how true wind (over water) can be calculated without it

Winds

[ronstory]

Well the new Airmar DX900+ ultrasonic hull sensor will measure the true velocity through the water, and not just the component of you velocity your paddle can measure inline with the longitude axis of the boat.

http://www.imarineusa.com/Airmar44-216-1-03.aspx

but they are expensive, over $1k.

The MDF should be able to determine the slip with the modern high precision GPS, but I have not been able to determine that. Does anyone know?