placement of anodes on shafts...

[vas]

talking to the 85yo father of the yard owner, one of the last traditional boatbuilders left in Greece, he spotted the anodes on the shafts of my boat and noted that I should never fit them halfway along the shaft but v.close to the P bracket. His explanation was that a weight (no matter how well balanced it is!) in the middle of a fastish rotating shaft will stress the bearings as it tends to turn slightly off centre ever so slightly...

Made sense as I heard it, will move the anodes 1 to 2 inches from the P bracket but was thinking what are the panel's opinion.
Obviously shaft dia vs free length are to be considered!

cheers

V.

 

[gravygraham]

We've fitted some shaft anodes for the first time this winter - and what you say makes sense. Might check mine before she goes back in.

 

[Divemaster1]

Never had the shaft anodes further away than 2" from the P bracket for those reasons..... Slightest un-even anode wear will cause imbalance... and I'd rather have it close to P bracket then far away...

 

[Bandit]

I use shaft anodes but I have seen them on other boats ride up the hull and damage hull by stern gland and also drop down on shaft to damage P bracket.

You dont want to obstruct the water flow over the cutless bearing in the p bracket or you will overheat the P bracket bearing.

Anodes can work loose when they start to reode and will move I always put a stainless jubilee clip above and below the anode to stop this with the tail of the clip tail trailing when the shaft is running ahead.

I place my anodes midway along the shaft as i thing the odds of the anode trapping a rope or net and getting jammed is much greater if its close to the p bracket.

I average 100 hrs a year and cutless bearings are 5 years old so probably in need of replacement anyway, but no serious noise vibration issue on 2 inch shafts. I can see how on a yacht with a 25mm shaft this could cause whipping.

 

[Robert Wilson]

I wish you had posted this on Monday!! Replaced two annodes on Tuesday. (last year's dropped off somewhere/sometime)
I placed this years' in the middle of the shaft, as previously, and I think I felt vibration going back to the mooring.

Bummer, I'll have to give the boat a run and most likely take them off and move them aft. And I'll have to get some more Loctite as I used the last drops on Tuesday. That means a trip to Inverness 70 miles away !!
On the other hand Bandit's post makes me wonder if I'm correct (and the vibration was caused by something else). Boat's should be simple!!

 

[Bandit]

RW

What condition are your cutless bearings in ?

You should have pretty well no movement when you lift them or at least no more than a mm.

Give it a decent run first to see if it settles down.

 

[Robert Wilson]

Good morning Bandit
I didn't make a detailed examination ( I shall in future! ), but whilst working on the prop I didn't notice any movement at all.
As far as I can recall there was no vibration in the last two years.
You're right, I'll give the boat a good run and check.
At least it's not a major problem to dry-out up here, I have a choice of two good quays and there's never a queue!
Thanks

R

 

[Neil_Y]

Makes sense to me, but there are many other factors that allow or encourage shaft whip/flex so probably not that significant in most boats.

 

[Bertramdriver]

Makes sense to me, but there are many other factors that allow or encourage shaft whip/flex so probably not that significant in most boats.

Replaced mine September after experiencing vibration at higher revs. Old ones were halfway down shaft and pretty degraded. Put the new ones immediately after P bracket. Now no vibration. What more can I say.