Another speed log question....

[MarcJ]

Hi,

I've just read the other thread with the speed log questions. I think that I have one of these fitted - here's a pic of the where it goes through the hull and the wire end that's attached:
View attachment 31719
View attachment 31720

Thank god I didn't undo that bolt, which I pondered - it would have been panic, I was on on my own with no mobile signal!

My question is - can I check to see if there's a paddle wheel or some sort of transducer underneath by checking for signals whilst moving? Is that a daft idea, in which case should I have a look first? - with a suitable plug ready (I'd have to make one).

Oh I should say, I have a Humminbird 383 combo sounder and GPS so I don't "need" the speed log, but it would be nice to know if there's one there, and maybe get the right display for it, in case the GPS fails. Also I have a basic TV signal detector that you would use to attach to an aerial cable, to tell you when the aerial is aligned, I wondered if that might show something...

 

[William_H]

I don't recognise the transducer and indeed it does not look like it is meant to come out. Often there is big plastic nut onto the outer casing that holds the removable transducer. Hopefully also you would have a plug made to fit in the hole and lock in. Not just a wooden conical plug. In fact it may even be a depth sounder transducer rather than speed log.
Speed log usually has a paddle wheel which rotates in slip stream. This has magnets around the outer periphery which either interact with a reed switch or a hall effect transistor magnetic field sensor. The red switch gives a short circuit or open circuit across 2 wires alternating as it rotates. The hall effect transistor type need a 5v supply an earth and signal output so 3 wires.
No a TV reception strength meter would be of no value at all.
Your best bet is to either try to find a way to withdraw the transducer. Be careful it may not be designed to come out. Failing that get someone underneath with mask and snorkel or dry the boat out to see what it looks like from underneath. As said it may be a depth sounder transducer which may not even come out to the surface of the hull.
Lastly it may be a doppler effect type ultrasonic speed transducer although I think they normally have 2 transducers.
If indeed it has a paddle wheel and no readout don't be surprised. Many of us have given up on paddle wheel type as they just foul up too easily so seldom work. So IMHO not worth pursuing. good luck olewill

 

[MarcJ]

The hall effect transistor type need a 5v supply an earth and signal output so 3 wires.
No a TV reception strength meter would be of no value at all.

Thanks Olewill, yes never thought it could be a depth sounder transducer.. sounds right! In case it's relevant the nut on the top felt like a plastic one..

 

[jwilson]

Looks to me to be an old Seafarer or similar spinning-dial depth transducer, internally mounted in a glassed in bit of plastic tube. Is there anything actually on the outside of the hull?

 

[prv]

I reckon depth sounder too. The internal fitting doesn't look right for something that screws down to keep the water out (that nut will just be the gland where the wire goes into the unit, not something you should unscrew to get the unit out) and the plug looks like a Belling-Lee ("TV aerial") connector so the cable is presumably coax. Older depth transducers used coax, I don't think logs did.

Pete

 

[john_morris_uk]

I reckon depth sounder too. The internal fitting doesn't look right for something that screws down to keep the water out (that nut will just be the gland where the wire goes into the unit, not something you should unscrew to get the unit out) and the plug looks like a Belling-Lee ("TV aerial") connector so the cable is presumably coax. Older depth transducers used coax, I don't think logs did.

Pete

I agree totally. Almost certainly a depth sounded transducer. If you have another one you can remove the whole gubbins. Otherwise why not use the glassed in tube to fit a new depth sounder transducer in. Castor oil was the traditional liquid used, but almost any oil will do.

A sailing school I worked for once, used to use washing up liquid.

 

[Fantasie 19]

I reckon depth sounder too. The internal fitting doesn't look right for something that screws down to keep the water out (that nut will just be the gland where the wire goes into the unit, not something you should unscrew to get the unit out) and the plug looks like a Belling-Lee ("TV aerial") connector so the cable is presumably coax. Older depth transducers used coax, I don't think logs did.

Pete

Looks exactly like the transducer I found on mine last year - same coax fitting as well....

Something like this... note, no hole through hull

The transducer should look a bit like this???

 

[MarcJ]

Thanks for the replies! I didn't check if the nut on top was actually plastic, I think it was though, which would make sense it being a transducer. (I'll be cursing if I get face full of water! )
Unfortunately I don't think my transducer will fit - but the good news is that my transducer does fire through the hull, thanks to Vic for getting me to try. I'll try the fit and see..

 

[William_H]

A friend bought a NASA depth gauge and removed the old rotating Seafarer depth sounder. He asked me to help install the new one. I found that the old transducer had the same plug as the new and worked quite well. So give it a go before you remove it.
Sorry I did not see the characteristic belling Lee plug first time. good luck olewill