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Old 24-05-2015, 13:28   #1
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Join Date: Apr 2012
Location: Cruising Mexico
Boat: 50' Herreshoff Ketch
Posts: 969
Faking Speed through water

At some point in the multitude of upgrades for our Raymarine e series chart plotter, I was able to use True Wind Speed and True Wind Angle using SOG (GPS Speed, no paddle wheel). A later update "fixed" this so it doesn't work that way anymore.

So I get that it won't be entirely accurate, but it would be a closer approximation than having nothing at all. Now they've added lay-lines, but it appears these are totally disabled without speed thru water.

I've got my PC setup on NMEA, could I get my PC to listen to NMEA and repeat the speed over ground as speed thru water, to trick my raymarine in to giving me TWA/TWS/Laylines?
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Old 24-05-2015, 14:56   #2
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Boat: Valiant 42
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Re: Faking Speed through water

This is a common question. IMO Raymarine are being bull headed about not permitting SOG to replace STW for true wind computations. There are some after market devices that will "spoof" the STW from the SOG data. I think this device can do it:

But you have to talk to the developer to be sure. It does a lot of things so it may be overkill for what you want.

There is another device that I can't recall the name that takes SOG data and outputs pulses to fake the Raymarine speed instrument into thinking it is connected to a paddlewheel. Then it outputs STW data because it doesn't know any better.
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