Lazy Log

[TiggerToo]

TT's trusted ST50 Log is getting a bit "slow". What I mean is: it "under-reads". I have tried the calibration procedure, to no avail (it has reached the "top"?).

There is no evident crud stopping its rotation when taken up from the hull.

Any ideas?

 

[Stemar]

A missing magnet in the impellor?

 

[Refueler]

I'm with Stemar if its a dual magnet impellor ... but if its a single magnet like most - maybe the magnet has lost most of its 'power' ... you can easily prise out old and epoxy in a new rare earth magnet ... eBay is full of all sizes of Neodynium rare earth magnets.

 

[Mistroma]

I'm with Stemar if its a dual magnet impellor ... but if its a single magnet like most - maybe the magnet has lost most of its 'power' ... you can easily prise out old and epoxy in a new rare earth magnet ... eBay is full of all sizes of Neodynium rare earth magnets.

I also thought that most had a single magnet. It could well have rusted away, I've seen that happen with windlass rotation sensors. Log sensors are usually quite simple with limited problem areas.

1) Paddle wheel doesn't spin rapidly enough due to build up of crud on sides or sometimes close to the shaft.
2) Sensor doesn't work at all, they used to be reed switches and either worked or didn't. I used to re-pot one every 4-5 years on an older boat
3) Magnet falls out or corrodes away

Option 1 and 3 are the best fit for the OP's problem. A freely spinning paddlewheel would encourage me to check out the magnet with a small piece of steel.

It's easy to check the older sensors by simply connecting a multi-meter and rotating the wheel slowly. Put the meter in a continuity test mode (beeps when probes touch) and you get a beep for each wheel rotation.

 

[prv]

I’ve had inaccurate speed before when the instrument head was sending a slightly under-spec voltage to the sensor. I don’t remember the proper figure off-hand (it’s not 12v) but the service manual is online and it’s easy to put a meter on the connections. I replaced the head unit and the log suddenly became reliable for the first time in years.

Pete

 

[TernVI]

Slime on the hull ahead of the paddle wheel can have a noticeable effect.

 

[TiggerToo]

Slime on the hull ahead of the paddle wheel can have a noticeable effect.

maybe it is me hoping... but I think I will try to correct this one, first!