Log problem with Raymarine plotter

[DrBob]

Anyone help with an annoying problem?

I have tactic instruments (log, wind etc) but wired into a Raymarine E120 and autopilot. Worked great for 2 years.

This summer without warning the boat speed the plotter is showing is much higher than the reading on the tactic instruments. The instruments are calibrated well - set up with zero tide and calibrated against on shore mile markers on the coast north of Eyemouth!! The instruments are still correct - ie the speed on a beat with a good wind is still high 6's.

At this speed though the plotter shows a boat speed of 10 or 11 knots. The SOG is the 6 + or - the tide. Whilst I normally dont bother with the boat speed on the plotter - I usually just use SOG - it is a pain as the calculation of tide by the plotter is based on boat speed so is way out. I think this is also wrecking the true wind angle on the plotter.

Today I also checked out the boat speed by connecting a PC to the Raymarine kit and on the Raytech software the boat speed was again too high at 10+ knots.

It looks to me that the tactic is feeding the correct boat speed into the Raymarine plotter but the plotter is now not understanding the value and registering something different. The high value does change up and down with increasing and decreasing "real boat speed".

Anyone got any ideas or suggestions which dont include chucking it all overboard and starting again!

/forums/images/graemlins/confused.gif

Dr Bob

 

[Danny]

The numbers suggest it may be a confusion between knots and kph - though I don't see how it could happen as the VHW sentence from the log gives the speed in both kn and kph.

 

[DrBob]

Danny,

is it possible to delete the log reading from the sentence received by the plotter and then re-instate it?

My plan is to connect up the PC running the Raytech software to the system and run it without the plotter and then without the auto pilot to see if the log reading on the PC returns to normal.

You are right that the difference in the numbers seems to be knots on the tactic and KPH on the plotter!

Dr Bob

 

[malcp]

DrBob, you say that the system (I assume including E120 and Tacktick) used to work ok, but then somethiing has changed 2 years ago. Is this correct?

Have you loaded any new s/ware on either the E120 or Tacktick in the last 2 years? If you have upgraded the E120 s/ware it is usually best to perform a factory reset before use, but you should backup your routes/wpts/trks etc beforehand and you will need to re-setup the plotter pages/screens/units etc again afterwards.

Suggest checking the speed / distance units on the E120 via the setup menu, if you haven't already.

You can see the NMEA sentences that the E120 is receiving, but you need to interpret the NMEA sentence yourself (not difficult). From the setup menu goto system diagnostics => external interfaces => NMEA and look at the buffer sub-menu. This should show a popup of the NMEA sentences received (and sent) by the plotter scrolling up the popup in real time. If you look at the received VHW sentences (probably prefixed $IIVHW) you then see a string of comma separated values. If you look at the correct value (field 5) in the format shown below you should be able to check what the Tacktick is actually sending.

VHW - Water speed and heading

1 2 3 4 5 6 7 8 9
| | | | | | | | |
$--VHW,x.x,T,x.x,M,x.x,N,x.x,K*hh<CR><LF>

Field Number:
1) Degress True
2) T = True
3) Degrees Magnetic
4) M = Magnetic
5) Knots (speed of vessel relative to the water)
6) N = Knots
7) Kilometers (speed of vessel relative to the water)
8) K = Kilometers
9) Checksum

Unfortuneately the field numbers above get misplaced when the post is displayed. The field numbers count from the left, using the commas as separators. Alternatively view this and scroll down to VHW.

Your plan to use the Raytech in place of the plotter is another alternative, but make sure Raytech is actually receiving the NMEA data signal from the Tacktick directly, not not bridged by anything else (I assume from your mail you bridged the Tacktick NMEA via the plotter? If so it doesn't exclude the tacktick outputting wrong data, as the plotter will just repeat what it receives).

Hope this helps

 

[Danny]

[ QUOTE ]
is it possible to delete the log reading from the sentence received by the plotter and then re-instate it?

[/ QUOTE ]Possible - but not at all easy! You'd need to catch the sentence, parse it and extract the field you want to change, change it and re-build the sentence and then re-calculate the CRC. Wouldn't bother - there must be an easier solution. I'd try malcp's suggestions first to see if you can pin down the problem a bit more.

 

[DrBob]

Thanks to both of you. Malcp, I will pm you to follow up.

Dr Bob