Simrad IS20

Does the IS20 Graphic calculate the TWS and TWA based Nmea data sent to it or is it just a repeater for wind data sent to it?

Regarding the discussion about using Speed Through Water, Speed Over Ground, Compass heading or Course Over Ground:

In IS20 the Speed Through Water and compass heading is regarded as one  speed vector measurement. Speed Over Ground and Course Over Ground, measured by the GPS, is considered another speed vector measurement. The difference between these two vector measurements is the Set and Drift vector.

The paddlewheel and compass must be aligned to get a correct measurement of the speed vector. The masthead wind sensor and the paddlewheel must be aligned to get a correct true wind angle/speed calculation. The compass must be aligned with the masthead wind sensor to get the correct wind direction calculations.

Course Over Ground and Speed Over Ground is never guaranteed to be aligned with the masthead wind sensor and therefore will not give a correct true wind calculation, but it's a fairly good number two measurement.

The problem with measuring the apparent wind is the inertial forces acting on the wind sensor on top of the mast. If the wind sensor is not well balanced, then you will get incorrect measurements when the boat is heeling, and you will also get a noisy measurement. IS20 uses the compass measurements to filter the apparent wind measurements without loosing the dynamics in the measurement. To check this you can see, when you are tacking, that the apparent wind angle is passing 0deg measurement in the same moment as the fore sail is shifting side.

To check the quality of the true wind calculations (how well the sensors are aligned, compass calibration and the balance of the wind sensor), you can look at the difference in wind direction measurement on port and starboard tack.

Øyvind

Are there any way of checking your SW version in the instrument?

I understand you can connect the instruments to a PC for upgrades’ but only dealers have the equipment, software and cable, other vendors lets the customers do this with a SD card or over a data link and it actually works i know. PC connection is a great thing to have also for navigation in the cabin.

Thanks for the bird picture.  Mine was a wren or something like that.  It wasn't immediately apparent (no pum intended) why the wind was rotating around the boat.

I have now connected the Garmin GPSMAP4008 using the NMEA2K and connecting it to the Simnet bus and to my surprise it worked immediately. I got all the wind data to the plotter and also waterspeed and depth. The IS20 multifunction instrument displays the plotter COG and so on. I made my one cable to connect the Garmin to the Simnet just by following the cables colours and using one part of a Simnet Cable and the other part of a Garmin cable to get the correct connectors.