Prop update

Firefly625

Firefly625

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For those that are interested, and for MarieK who particularly asked....

Well here it was;

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...and now fine for another season, camera flash has highlighted imperfections but blade surfaces are actually now pretty smooth and certainly whatever anyone else thinks I'm happy to stick this on my boat for another season...or two;

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I dont want to be a kill joy or anything but I think you've got an electrical problem.
Probably a poor galvanic connection between your props and the anodes.
Where are the anodes?
Are there shaft anodes?
Are there brushes between the shafts and main bonding system - inside side of the glands?
 
Looks a great job Firefly. I agree, stick it on for another season, or ten.

Hurricane, keep up chap :-), see earlier threads, the pitting was caused by an earlier electrolysis problem that has been diagnosed and cured, so shouldn't recur

Firefly, your pics are too wide. 600/640 pixels is about right :-)
 
jfm said:
Looks a great job Firefly. I agree, stick it on for another season, or ten.

Hurricane, keep up chap :-), see earlier threads, the pitting was caused by an earlier electrolysis problem that has been diagnosed and cured, so shouldn't recur

Firefly, your pics are too wide. 600/640 pixels is about right :-)
Click to expand...

Thanks jfm, a lot of effort but certainly enjoyable.. :)
...........and thanks for photo advice, I will try to amend!!

Hurricane, thanks but as jfm says I have sorted electrolysis issue, but FYI this damage was done in a 5 month period...
 
Firefly625 said:
Thanks jfm, a lot of effort but certainly enjoyable.. :)
...........and thanks for photo advice, I will try to amend!!

Hurricane, thanks but as jfm says I have sorted electrolysis issue, but FYI this damage was done in a 5 month period...
Click to expand...

Sorry, I missed the earlier thread.
I had a similar problem when we bought a previous boat.
Fixed the problem - shaft brushes
And bought some new props.
Kept the old ones and one day decided to see if they could be cleaned up.
Hamble Props did a great job so the boat was sold with two working sets of props.
So, as jfm says - they should now last - now that the root cause is fixed.
Our old (repaired pair) were as good as the new ones.
 
Hurricane said:
Sorry, I missed the earlier thread.
I had a similar problem when we bought a previous boat.
Fixed the problem - shaft brushes
And bought some new props.
Kept the old ones and one day decided to see if they could be cleaned up.
Hamble Props did a great job so the boat was sold with two working sets of props.
So, as jfm says - they should now last - now that the root cause is fixed.
Our old (repaired pair) were as good as the new ones.
Click to expand...

Hi Hurricane, ...well funny you should say that, the shaft brushes on my Hardy were knocked to one side and probably 3" away from from the prop shaft when I got the boat..! re-fitted them but to be honest old set (probably original) had lost their spring (got a bit seized due to rusty spring) so although resting on shaft quite well didn't clamp on as they should have so renewed shortly after getting boat. Tested connection between prop shaft and anode when boat was pulled out the water and now 100% OK, so shouldn't experience the same issue.
Therefore for this reason I have taken the time to refurbished the old prop as I would hate to buying a new prop and have the same issue, however unlikely that would seem, but just in case I have missed something!!!
 
I've always had these shaft brushes and kept them well maintained for good measure, but I gotta say, I dont really understnad them. The idea is to earth the prop shaft and prop to the ship's earth and the anodes. But the propshaft is bolted to the crankshaft via the gearbox, and the engine block is earthed. So why have these brushes? Is it because the film of oil in the gearbox and in the crankshaft bearings acts as an insulator, hence the shaft and prop are not connected to earth with a sufficiently low resistance? I dunno.

If it's because of the plastic sacrificial connector twixt prop shaft and gearbox (that smashes if you prang a rock, to save the gearbox) you can just connect the metal to metal, bridging over the plastic, using a very short link cable between the boltheads

Firefly you can test the continuity twixt your prop and the anodes with a good multimeter, to check it is all well bonded, as a rough and ready extra check. Of course, you want almost zero resistance, not merely "continuity", so you gotta use the multimeter correctly to determine this
 
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Firefly625 said:
Hi Hurricane, ...well funny you should say that, the shaft brushes on my Hardy were knocked to one side and probably 3" away from from the prop shaft when I got the boat..! re-fitted them but to be honest old set (probably original) had lost their spring (got a bit seized due to rusty spring) so although resting on shaft quite well didn't clamp on as they should have so renewed shortly after getting boat. Tested connection between prop shaft and anode when boat was pulled out the water and now 100% OK, so shouldn't experience the same issue.
Therefore for this reason I have taken the time to refurbished the old prop as I would hate to buying a new prop and have the same issue, however unlikely that would seem, but just in case I have missed something!!!
Click to expand...

Our boat was a Sealine
Our shaft brushes were held on with a flimsy "castle shaped" plastic fitting which was simply attached to the gland fitting with a jubilee clip - totally useless.
So, we had a bar shaped bracket made up and fitted to one of the gland bolts thus providing a really rigid fixing for a new set of brushes.
There's a place on the industrial extate up behind the RYA's offices that has a load of brush type fittings - cant remember their name but I might be able to find them if you need to know.
I would definately try and get a really good connection between the shafts and the bonding - worth spending a few quid to get this right - and its only a few quid as well - make sure that the springs are all tight and that you are getting a good robust electrical connection. The currents in this circuit are very small and driven by a very low voltage so the connections must be really good.

This definately fixed our problem.
 
jfm said:
I've always had these shaft brushes and kept them well maintained for good measure, but I gotta say, I dont really understand them.
Click to expand...

jfm, sorry, just wanted to pick you up on this statement....have I at last found something you don't know about? I don't believe it! :D

Firefly you can test the continuity twixt your prop and the anodes with a good multimeter, to check it is all well bonded, as a rough and ready extra check. Of course, you want almost zero resistance, not merely "continuity", so you gotta use the multimeter correctly to determine this
Click to expand...

Well I did check with a good multimeter and do have almost zero resistance... if I was using it correctly..:o


...but as for indeed why the prop and shaft is not earthed through gearbox.... no idea!
 
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