Hello,

I took at look at the AP44 manual ( https://ww2.simrad-yachting.com/Root/Simrad-Documents/AP44_docs/AP44_OM_EN_988-11189-002_w.pdf) and it looks like trip logs should be able to accomplish the distance logging you're hoping to retain.  Have you checked those out?  Is there a problem with the way they're implemented?  

As far as speed I'm not sure the process of changing the source but the manual indicates the autopilot will move from using STW to SOG if STW is unavailable. 

Use SOG as boat speed
If boat speed is not available from a paddle wheel sensor, it is
possible to use speed over ground from a GPS. SOG will be
displayed as boat speed and used in the true wind calculations and
the speed log.

I have a feeling the issue is that switch may only happen when the STW paddle-wheel sensor leaves the network.  I also suspect you're probably using a paddle wheel that is also providing water temp and possibly depth info such that you wouldn't want to disconnect it.  Given the manual's clear mention of the capability to switch from STW to SOG it may be worth an inquiry to Simrad.

Good luck!

Ben

Hi Ben,

Thanks for your reply. I got a "similar" reply from SIMRAD support (only similar because they gave me a wrong path to this setting). Here is the right path:

Settings>Calibration>Boat Speed>Use SOG as boat speed

Unfortunately, I fear this will apply to all calculations (true wind, tide, autopilot rudder response, etc.). While this is a nice back-up solution for when the paddlewheel is fouled, that is not exactly what I wanted.

Still no reply from SIMRAD concerning the distance log. I have the 2 trip logs working (they both accumulate time and distance) but the distance log does not move. When I check the network configuration, in the source list there is a 'distance log' entry, when I enter there, I can only see 'no devices available' for this (even after updated the sources).

When I compare AC42 and NAC3 manuals, I do see that PNG 128275 is no longer handled on NAC3 (arrrg). We have quite a long list of instruments on board and none can do distance log??

I can set a distance log value manually (it does not move when sailing) but it does not disappear between reboots... so it is stored somewhere for sure. Maybe it is a bug?

Hi Ben,

Thanks for your reply. I got a "similar" reply from SIMRAD support (only similar because they gave me a wrong path to this setting). Here is the right path:

Settings>Calibration>Boat Speed>Use SOG as boat speed

Unfortunately, I fear this will apply to all calculations (true wind, tide, autopilot rudder response, etc.). While this is a nice back-up solution for when the paddlewheel is fouled, that is not exactly what I wanted.

Still no reply from SIMRAD concerning the distance log. I have the 2 trip logs working (they both accumulate time and distance) but the distance log does not move. When I check the network configuration, in the source list there is a 'distance log' entry, when I enter there, I can only see 'no devices available' for this (even after updated the sources).

When I compare AC42 and NAC3 manuals, I do see that PNG 128275 is no longer handled on NAC3 (arrrg). We have quite a long list of instruments on board and none can do distance log??

I can set a distance log value manually (it does not move when sailing) but it does not disappear between reboots... so it is stored somewhere for sure. Maybe it is a bug?

Best regards,

nibheis

Hi, some news!

I got the confirmation from SIMRAD that 'Use SOG as boat speed' only applies to true wind calculation, which is what I wanted. When this is active, tide is still calculated with SPD, and autopilot computer uses in order: SPD, SOG or the manual override. I confirm that it seams to work that way on my system.

Concerning the distance log, SIMRAD just ignores my questions for the last 2 weeks. On my side, I kept searching and I discovered that my DST800 transducer keeps a distance log (PNG 128275). I can see it (and it logs the miles) when I am digging into the network and I ask for detailles information on the DST800 from my SIMRAD instruments.

So, the data (distance log) is there... I have a device that can handle it... why cannot I see this device (DST800) in the source selection menu?!? Why is SIMRAD so silent about that?

Best regards,

nibheis

I spent a long time reading through manuals, talking to people on forums, and emailing tech support for both Raymarine and Navico (Simrad) around TWA and TWS. Recently I replaced an old wind instrument with the LCJ Capteurs CV7 and WindyPlug during my major mast work and I wanted to understand how true vs. apparent wind direction and speed were calculated. 

It turns out each manufacturer does it just a tiny bit differently than the others, but on the whole, they all rely on STW from some source as the primary method to calculate these.

I had originally thought that TWA and TWS were actually values created on the NMEA 2000 network, but I found that very rare with configurations. In fact, the only devices I could find that did this were all-in-one units like the Airmar WeatherStation ultrasonic units, which have a GPS and wind detection combined together, and as such they use that info to create TWA and TWS internally, and actually send those PGNs onto the NMEA 2000 network. Some would argue that using GPS for this is not as accurate as STW (and I found plenty of those arguments in my research) but regardless of that, there are very few devices that actually produce that data and put it on the network.

For both Raymarine and Navico, I found that the instruments themselves use STW + AWA/AWS to produce TWA & TWS. I tested Raymarine MFD's, i70s and p70s instruments, B&G Vulcan MFDs and Triton instruments. All of them produced pretty similar results, but never put any of their data on the network - only displayed it on the device.

Both Raymarine and Navico have the configuration option you found, which is to force it to use SOG if STW is not available. On both, I found that you have to manually choose to use SOG, and that it won't fall back to SOG if STW is missing. I didn't have Garmin to test, but someone said it does fall back in certain situations - I can't confirm that.

The weird thing is that even within a single vendor setup, such as a Raymarine Axiom, several i70s instruments, and a p70s autopilot instrument, each of them calculates TWA and TWS on their own, and can be configured differently. I suppose that could be nice if you wanted one unit to use SOG and one to use STW, but it seems like that could cause some confusion if you forget!

This conversation started with another sailor who was considering replacing their wind instrument, but was concerned that they would lose TWA and TWS based on manuals and support communication from a vendor.

At least for the more modern instruments, it appears those calculations are done internally, even between shared vendor equipment. Older instruments definitely have more requirements/limitations, but the newer ones should be pretty compatible with changes/upgrades.

At the risk of sounding cranky, let's please acknowledge that the "True Wind" being calculated by only applying STW to AWA/AWS is a misnomer. It would be far more precise to call it Sailor's True Wind, True Wind relative to Water, or simply Sailing Wind. That's because the True Wind I'm interested in as a powerboater -- which is also what meteorologists and everyone else ashore think of as True Wind -- is properly calculated on a boat by applying SOG, COG and Heading to AWA/AWS.

Some boat instruments use at least part of that calculation to produce what's often called Ground Wind, as in True Wind relative to Ground. Sailor's True Wind is only true at that moment on their boat, unlike, say, True North, which is constant for all of us. So in my view, boat electronics True Wind is only what it is because sailors got there first, and Ground Wind is True True Wind.

Harumphf 😉

PS Many Panbo conversations on this topic, including:  https://panbo.com/the-equinox-celestial-mechanics-pesky-true-wind/