Changing source of distance log on Raymarine plotter from paddle wheel to GPS

[tudorsailor]

First off, let me say that I have read the manual and cannot find the answer to this question.

I have a Raymarine C125 Multifunction display running Lighthouse II. I recently noticed that the trip distance does not show if the paddle wheel log is not spinning when we start off. I am aware that the speed through the water tends to under read compared to Speed Over Ground which comes from the GPS. As a result the trip and total distance shown are less than the true distances
I see in the manual that one can select sources of GPS data but I cannot find how to change the source of distance travelled between paddle wheel log and GPS in the manual. Could someone tell me how to do this?
Thanks
TudorSailor

 

[AntarcticPilot]

I asked a similar question a couple of years ago, and the answer was "you can't", at least, not without delving into microprocessors and software. It's on here at Can the ST60+ wind instrument be adjusted to use COG and SOG

 

[Sandy]

Don't be deceived by GPS distances! They rely on the number of data points you record. Back in the early days of handheld GPS some mountaineering pals were a tad pissed off when one had walked 2 km more that the other and they had walked the same path side by side all day. Once I looked at their GPS I saw that one had it set to record the position every 5 mins and the other was auto based on time and distance. I have my Garmin CP set to one datapoint every 6 mins, 10 an hour, and don't get hung up on knowing that a passage was 50.38 or 55NM.

There will always be a difference between STW and SOG as the tide has an affect. I usually motor at 5.5 knots STW but my SOG can range from 3 - 7.5 knots.

 

[fredrussell]

Don't be deceived by GPS distances! They rely on the number of data points you record…

…I have my Garmin CP set to one datapoint every 6 mins, 10 an hour, and don't get hung up on knowing that a passage was 50.38 or 55NM.

What? Do you mean to say that you have made your chartplotter less accurate than it might otherwise be? A modern gps ‘powered’ device should be more accurate than that surely?

 

[Sandy]

What? Do you mean to say that you have made your chartplotter less accurate than it might otherwise be? A modern gps ‘powered’ device should be more accurate than that surely?

No. The GPS accuracy cannot be adjusted.

I have reduced the number of datapoints that are stored as I have found that when set to Auto I run out of storage space in RAM and on passages greater than five days. The last thing on my mind is to remember to backup to data card and clear the memory. It is from the stored data points that the distance and average speed are calculated.

I find it interesting that people are so hung up about the accuracy of their GPS. I am a huge fan of the MK I eyeball and tend to use that when doing close quarter work.

At a talk by the Royal Institute of Navigation, I'm an ex-member, on GPS and how accurate is was I raised the question, 'Was it any use when the survey date on some of the charts I use is in the 18th Century'. There was a very pregnant pause in the speakers reply. By the way if you can get to a RIN talk on GPS they are well worth attending.

 

[Refueler]

First off, let me say that I have read the manual and cannot find the answer to this question.

I have a Raymarine C125 Multifunction display running Lighthouse II. I recently noticed that the trip distance does not show if the paddle wheel log is not spinning when we start off. I am aware that the speed through the water tends to under read compared to Speed Over Ground which comes from the GPS. As a result the trip and total distance shown are less than the true distances
I see in the manual that one can select sources of GPS data but I cannot find how to change the source of distance travelled between paddle wheel log and GPS in the manual. Could someone tell me how to do this?
Thanks
TudorSailor

First - I have to comment about : "I am aware that the speed through the water tends to under read compared to Speed Over Ground which comes from the GPS" ??????? That is not the case. Its quite easy for STW to be greater than SOG ... all you need is to be heading into a current ... then your STW is still your boat speed in water but the water you are in is moving opposite way to you ... so SOG is LESS.
If the current is WITH you - then STW will less than SOG.

OK - Distance run ... does your Plotter not keep a running 'Track total' ?? OK - maybe not displayed - but it should have somewhere a running total track ?

 

[tudorsailor]

First - I have to comment about : "I am aware that the speed through the water tends to under read compared to Speed Over Ground which comes from the GPS" ??????? That is not the case. Its quite easy for STW to be greater than SOG ... all you need is to be heading into a current ... then your STW is still your boatts speed in water but the water you are in is moving opposite way to you ... so SOG is LESS.
If the current is WITH you - then STW will less than SOG.

OK - Distance run ... does your Plotter not keep a running 'Track total' ?? OK - maybe not displayed - but it should have somewhere a running total track ?

Since I sail in the Med, significant currents are not common. I am aware that if I am going with the current then SOG will be greater than STW.
TS

 

[fredrussell]

No. The GPS accuracy cannot be adjusted.

I have reduced the number of datapoints that are stored as I have found that when set to Auto I run out of storage space in RAM and on passages greater than five days. The last thing on my mind is to remember to backup to data card and clear the memory. It is from the stored data points that the distance and average speed are calculated…

.

Ah, I see. It’s of interest to me as I have the same brand chartplotter as yourself.

 

[RupertW]

Since I sail in the Med, significant currents are not common. I am aware that if I am going with the current then SOG will be greater than STW.
TS

But they do exist - half a knot surface current between islands or around headlands is not uncommon after a few days of a strong Bura/Mistral/Meltemi and I can think of places even in Greece where tidal flow is significant.

 

[Refueler]

No. The GPS accuracy cannot be adjusted.

Correct but the positional calculations based on the GPS rec'd data can be affected.

Many GPS sets can have iterations / averaging user adjusted. So you can have unit calculating over extremely short intervals or you can set it to longer intervals. The increasing of time between can lead to positional fixes being inaccurate at times ... whereby more frequent can improve positional accuracy ...... because all data given to you is based on 'averaging'. As I say - some sets allow you to not only alter the time interval of positional calculations - but also the averaging .....

OK - I accept that most that yotties come across may only allow one of those to be altered ..... as to what its called on 'your' plotter - I cannot advise.

 

[dunedin]

First off, let me say that I have read the manual and cannot find the answer to this question.

I have a Raymarine C125 Multifunction display running Lighthouse II. I recently noticed that the trip distance does not show if the paddle wheel log is not spinning when we start off. I am aware that the speed through the water tends to under read compared to Speed Over Ground which comes from the GPS. As a result the trip and total distance shown are less than the true distances
I see in the manual that one can select sources of GPS data but I cannot find how to change the source of distance travelled between paddle wheel log and GPS in the manual. Could someone tell me how to do this?
Thanks
TudorSailor

I simply use Ground Trip 1 as the log. (There are also another 2-3 Trip registers, I think, but never needed to use them). This gives the total distance since last reset, and is based upon GPS not the paddle wheel.
Used successfully so far for 8 seasons and over 15,000nm so far.

EDIT: Page 269 of my Lighthouse 2 manual refers - it lists all data types for Distance. Perhaps Ground Log could also be used

 

[PaulRainbow]

I have reduced the number of datapoints that are stored as I have found that when set to Auto I run out of storage space in RAM and on passages greater than five days. The last thing on my mind is to remember to backup to data card and clear the memory. It is from the stored data points that the distance and average speed are calculated.

I don't think that's correct Sandy. If you turn tracking completely off the plotter still logs speeds and distances.

 

[dunedin]

I don't think that's correct Sandy. If you turn tracking completely off the plotter still logs speeds and distances.

Paul, you are Correct. I think Sandy has muddled the Track function with the Distance functions

 

[Pye_End]

Calibrate log so that it is correct?

 

[john_morris_uk]

Calibrate log so that it is correct?

My first thought.

Since I sail in the Med, significant currents are not common. I am aware that if I am going with the current then SOG will be greater than STW.
TS

Or is it simply that your log isn’t calibrated?
I haven’t seen a measured mile in the med but they must exist?

 

[Sandy]

I don't think that's correct Sandy. If you turn tracking completely off the plotter still logs speeds and distances.

Yes, you are correct. I use my plotter data in a different way and clear down the total distance, average speed and moving time after each trip.

I'll need to leave the total distance sailed for a few hindered NM and see if there is a difference between the CP and the saved data on my spreadsheet next year. Not that it is of any use to man.

 

[tudorsailor]

I simply use Ground Trip 1 as the log. (There are also another 2-3 Trip registers, I think, but never needed to use them). This gives the total distance since last reset, and is based upon GPS not the paddle wheel.
Used successfully so far for 8 seasons and over 15,000nm so far.

EDIT: Page 269 of my Lighthouse 2 manual refers - it lists all data types for Distance. Perhaps Ground Log could also be used

View attachment 144487

That might do it! I will set the distance to use ground log and trip and see what happens. Hopefully it will not reset the log to zero.

Slightly frustrating that I am not on board till April. THanks

 

[dunedin]

Calibrate log so that it is correct?

Clearly it is worth the water log being calibrated - not least to get an accurate Speed Through Water.

BUT, is the Distance Through Water (DTW) the best figure for the primary Log recording these days?
Fifty or more years ago there was no alternative to the DTW for the ships log - though, unless doing a transatlantic with a towed log, most of the mechanical through hull or GRP rod on the stern based logs were laughably inaccurate.

Nowadays we have the choice of DTW or GPS based Distance Over Ground (DOG) as the primary log reading.

For me it is definitely DOG as primary. I do route planning based on a chart, and measure courses (True) and distances on the chart which are DOG. Hence I record the distance sailed based upon the distance actually travelled. This give me the best indication of where I am, and matches best to the reciprocal of the distance to go (DTW).

I have both if I needed them, but it is only the GPS Log reading that gets referred to and recorded in my hand written ships logbook.
Interestingly, after 15,000nm or so the DTW Log is around 1,200nm less than the main log.
A bit of this will be due to occasionally the log impeller needing a nudge at speed to clear harbour debris. But the majority reflects the fact that in strong tidal waters, a sensible skipper generally goes with the tide, so the DOG will be greater than the DTW.

 

[GHA]

BUT, is the Distance Through Water (DTW) the best figure for the primary Log recording these days?

As ever - it depends .... unless you are on a web forum where the universe is completely black and white & one size fits all....?
Offshore passages I usually check the log against a walker trailing log for 5/10 miles in the hope that will be fairly accurate. . Then every midday boat time is great excitement to see what the days run has been & do we have the current with us.
Best so far has been 100Nm on the log, 170Nm GPS distance ?
But day to day after Biscay, GPS distance works fine, water log is nice but not the end of the world when it's stopped working. Again. ?

 

[Refueler]

For me .....

STW is good to tell me the ability of the sails and or engine as they are pushing through a body of moving water.

SOG is good to know when I can go prop up the bar !!