Broken Impeller Testing?

[Simon F]

Hi All,

My Clipper Duet depth/log has stopped displaying speed (it shows 0.0knt) Handily I was able to remove the impeller without any water coming in and it seems to turn, although perhaps not all that confidence inspiringly, is there any way to test it before I buy a replacement? Is there anything else it could be, besides a faulty impeller?

All the best

Simon.

 

[neil_s]

My ST30 does that sometimes. It's always a tiny bit of barnacle shell hidden somewhere around the paddle wheel. It must spin with no friction in order to register correctly. Try giving it a good wash with hot soapy water and a toothbrush.

 

[Stemar]

How easily does it turn? If you can't blow it around, it's probably too stiff. The other possibility is that there should be magnets in the tips of the vanes. I can't remember if it's all the vanes or just some, but it isn't unknown for them to go AWOL, but it would be unusual for them all to bugger off at once

 

[MarkCX]

Fairly certain it’s one magnet from when I had a Nasa log. My magnet disappeared and and I bought a new impeller, with the added benefit that it spun much better than the old one.

 

[Simon F]

My ST30 does that sometimes. It's always a tiny bit of barnacle shell hidden somewhere around the paddle wheel. It must spin with no friction in order to register correctly. Try giving it a good wash with hot soapy water and a toothbrush.

Thanks Neil, I'll try that. S

 

[neil_s]

Another possibility is a barnacle on the hull fitting - you might have to jump overboard to check that, though!

 

[Simon F]

Another possibility is a barnacle on the hull fitting - you might have to jump overboard to check that, though!

Fine with me!

 

[knuterikt]

My ST30 does that sometimes. It's always a tiny bit of barnacle shell hidden somewhere around the paddle wheel. It must spin with no friction in order to register correctly. Try giving it a good wash with hot soapy water and a toothbrush.

Aftewards you can test by spinning it by hand while your crew check the instrument.

 

[William_H]

Yes on my Smiths paddle wheel I could get an indication over 10 knots with a hearty blow on the wheel. ol'will

 

[vyv_cox]

The magnet on Nasa log impellers corrodes and falls off after a few years. It has happened to me and is probably doing so as we speak with my boat locked away.

 

[cloud-nine]

Two of the paddlewheel vanes should contain magnets. Bring a steel screwdriver close and it will cause the wheel to move. You can remove the wheel by carefully pushing
out the axle with suitable pin. Growths on the axle (which can cause the wheel to stick) can be removed with a pan scrubber. The body of the unit just contains a coil of wire. To check it electrically you need
a meter connected across the terminals of the coax plug. It should read between about 50 to 100 ohms.