Raymarine Log

Blue5

Blue5

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Went out yesterday for the first time with the log in since our haulout and noticed I was getting some serious over reading figures. On going out of Portsmouth 1 hr after low water I was getting 11kts, I would have expected to see 6kts and returning 2hrs before hw I was still seeing 10.5kts where I would have expected to see the log reading below the SOG.

To complete the picture, ground trip for the sail was 11nm, log 25nm !!

I realise I need to recalibrate the log but why should I be getting such a large discrepency, what affects the calibration? all other functions, depth, wind speed, temp seem OK.
 
When did you last calibrate the log? Was the log impeller 'clean' when it was last calibrated?

If the log was calibrated with a 'dirty' impeller and the impeller is now clean, that may account for the difference.

It is a big difference, though.
 
NDH said:
Went out yesterday for the first time with the log in since our haulout and noticed I was getting some serious over reading figures. On going out of Portsmouth 1 hr after low water I was getting 11kts, I would have expected to see 6kts and returning 2hrs before hw I was still seeing 10.5kts where I would have expected to see the log reading below the SOG.

To complete the picture, ground trip for the sail was 11nm, log 25nm !!

I realise I need to recalibrate the log but why should I be getting such a large discrepency, what affects the calibration? all other functions, depth, wind speed, temp seem OK.
Click to expand...

Are you sure it's reading knots and not kilometres per hour?
 
Crazy log?

You don't say what model it is BUT IMHO it needs to be cleaned and calibrated every couple of years by running a measured distance.
Don't be misled by the remains of markers near Gilkicker: the nearest official distances are in Chichester Harbour and up Southampton Water, both are on the charts.
 
Playtime said:
When did you last calibrate the log? Was the log impeller 'clean' when it was last calibrated?

If the log was calibrated with a 'dirty' impeller and the impeller is now clean, that may account for the difference.

It is a big difference, though.
Click to expand...

The log was last calibrated about 12 months ago, I do not leave the log in and I have not cleaned it since it was was used prior to lift out when it appeared to be OK.

Ken - Definitely NM
 
NDH said:
The log was last calibrated about 12 months ago, I do not leave the log in and I have not cleaned it since it was was used prior to lift out when it appeared to be OK.

Ken - Definitely NM
Click to expand...

I wondered, because 12 kph is 6.5kts. And my old Raymarine windspeed sometimes used to switch, all by itself, from kts to metres per second.
 
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