Shaft anodes in tandem?

[alan_d]

My shaft anode is part worn and I intend to fit a new one. Being something of a skinflint, I wondered about leaving the old one in place and fitting the new one next to it (there is plenty of room on the shaft). That way I reckon I would get some benefit from the remains of the old one until it drops off, at the same time reducing the rate of wasage of the new one.

I have never heard or read of anyone doing this. Is it a sensible thing to do, or am I missing something?

Alan

 

[tcm]

nope, sounds fine to me. You could have a whole load of them i reckon.

Advanced skinflinting involves making an over-the side anode from discarded lumps of anode found in the shipyard and melted down in a reasonably clean sawn-off paint tin. Completely free!

 

[Bajansailor]

I have often seen propeller shaft anodes in tandem on the large twin screw sportsfishing boats here, and it does seem to make sense.
However they usually have a significant gap between the anodes - I would have thought it would be better if the anodes were literally butting together (that should reduce turbulence, and hence resistance a wee bit?).
Extending this way of thinking, then if you put the new one ahead of the old, then the resistance should be less (?), re less turbulence, as the new one should be relatively smooth, whereas the old one is probably quite rough and bumpy.
The resistance difference (if any) would be rather small though.

There is discussion re how you can over-protect a boat with zincs - but could this also apply to a propeller shaft where there is such a variety of metals to be protected (re the prop and the shaft), with lots of surface area exposed (hence rapid rate of anode erosion), and a relatively small anode (or two) to do the job?
I am thinking that 'the more the merrier' re prop shafts - what do other forumites think?

Re TCM's advanced skinflinting above, I have collected up old disc anodes (discarded from trim tabs and rudder blades, often with very little wear), threaded them on to a long eyebolt, and attached the new 'anode' to mooring chain with reasonable results - I am sure it would also work reasonably well if hung over the side.

 

[PCUK]

If your shaft happens to be 1.5 inch diameter I have a new shaft anode on the For Sale Forum at half list price!
Just a thought!!!

 

[ex-Gladys]

It's what I did last year. I have a prob wher the shaft anode goes quite quickly, I couldn't get a big MG Duff anode so put two of the little ones on and they were hanging by a thread (only about 30% left). This year I have two MG Duffs, which I will put on, and if they aren't too bad next year hope I can leave them alone.

 

[dombuckley]

As anodes erode, they will eventually loose grip on the shaft. When this happens, they will move down the shaft and grind against the P-bracket and cutless bearing. If you keep the old one on, therefore, you should fit the new one "downhill" of the old one.

 

[alan_d]

[ QUOTE ]
If your shaft happens to be 1.5 inch diameter I have a new shaft anode on the For Sale Forum ...

[/ QUOTE ]

25mm, I am afraid.

Thanks to all who responded.

Alan

 

[Borden]

"As anodes erode, they will eventually loose grip on the shaft. When this happens, they will move down the shaft and grind against the P-bracket and cutless bearing".

To avoid grinding your P bracket try this simple tip. Fit a quality hose clip on the shaft either side of the anode. This will stop it attacking the P bracket when it wears. The anodes wear from the inside out so become loose when worn. The hose clips will just act as stoppers. Bear in mind that a loose anode is almost a useless anode as good contact with the shaft is vital.

Coin

 

[vyv_cox]

<<< The anodes wear from the inside out>>>

Do they? I've been using shaft anodes for several decades now and I've never seen one wear from the inside. Here's one that has seen some service, still firmly attached to the shaft.

If your anodes come loose and rattle on the shaft, it's because they weren't attached properly in the first place. Fit them to the shaft, tighten the bolts, then knock each half together using two hammers. Tighten the bolts and repeat the process, until they don't tighten any more. The anode will remain locked in place by the steel insert collar until there is no zinc left.

 

[PCUK]

Vyv, what happened to the locking part of your Stripper? Mine got ripped off by a 20 metre fishing net!

 

[vyv_cox]

I picked up a length of blue polypropylene rope, about 14 mm diameter, coming out of Pollensa Bay. It seemed like it was part of a mooring, as the other end disappeared into the bottom and was very reluctant to come out. We started sailing shortly afterwards and could see the rope trailing behind. Arrived in Menorca it took me about half an hour to get it off, when I was able to prove the old story that a carving knife is by far the best way to do it.

Subsequently I replaced the P-bracket. There was a little dezincification around the screw threads but none elsewhere, I cut it up to check.