Navman Speed Log being over optimistic

[SP2]

We have a Navman Log on Galadriel with a through hull paddle wheel. Last year it appeared to be fine - this year with the paddle wheel all cleaned and polished it is reading probably about twice the likely speed we are doing (let's face it, a 36 year old 25 foot fin keel boat with 9 HP on tap is unlikely to be hitting 8 knots when the tap isn't even full on).

Before I invest in a replacement, has anyone any ideas?

 

[ianat182]

The only time we've hit 9 knots was reading our Navman GPS en route for Yarmouth with a F3-4 on the beam, cruising chute and about 2kts of tide beneath us, but we didn't need to adjust a thing the whole journey from Calshot Spit - Brilliant!

Are you able to compare the reading with your GPS? we don't have a log and use GPS for our speed checks.(We are also a W.Tiger - T182 )

As you are getting a reading I guess the little magnetic blob on the paddlewheel is still there,I don't know if it is a metal or metallic paste but it can be knocked off. Usually the problem is the reverse, where weed and marine life make their home in there,so under-reading or nothing registering at all.

ianat182

 

[SP2]

Hi Ian,

Yes we have a Garmin GPS and a Standard Horizon Chartplotter so have good speed over ground data. The paddlewheel was fouled but cleaned before our first trip this season.

Its not really a problem as from last season we have a pretty good idea of speed through the water and with some tidal calculations can work it out.

 

[SJF]

Assuming you have the Navman Speed 3100 you need to run its speed calibration which can be found on page 8 of the manual http://www.plastimo.com/pdf/SPEED3100(English).pdf

The other Navman models also have calibration settings that you can use to adjust the speed reading and their manuals are available for download from http://www.plastimo.com/uk/services/notices.php if you don't still have your paper manual.

 

[SP2]

SJF comes up trumps!

SJF,

Thanks - I've not got the instructions for this instrument (fitted to Galadriel by the last owner) - so now I know what to do.

The Forum does it again...

I will have a fiddle in the week when I go out and get it reading more accurately.

No more 8 knots for us, then