Prop Shaft anode

[Crinan12]

Hi

Does it matter that the prop shaft anode I'm about to fit doesn't clamp completely round the shaft? There is a gap as you can see from the photo

It's a 1inch shaft and a 1 inch anode.

It's just I'm sure the last anode fitted right round the shaft with no gap.
Thanks

 

[VicS]

A small gap wont matter.
It's better that there is small gap than the two halves coming together before they are really tight on the shaft.

Are you familiar with the "2 hammer" technique of ensuring that the two halves are really tight against the shaft?

 

[V1701]

That's shrinkflation for you...

 

[Crinan12]

Great thanks. And yeah I know about the 2 hammer thing actually. Last anode I fitted fell off pretty quickly and it's only when I research it I found out about that trick.

 

[Bodach na mara]

I'll be fitting one soon myself. The last one lasted two (?) years and fitted with less of a gap than the one in your photo. Mine is a 1 inch shaft as well.

 

[Crinan12]

Apparently I don't even need a shaft anode (according the manufacturer of the propellor).

But the previous owner told me it was essential.

So I thought I might as well just keep fitting them.

 

[vyv_cox]

Could be worth abrading the shaft for good electrical continuity. It looks a bit coated.

 

[Tranona]

Apparently I don't even need a shaft anode (according the manufacturer of the propellor).

But the previous owner told me it was essential.

So I thought I might as well just keep fitting them.

I could well be you could do without it. What propeller is it? and does the anode erode? That arrangement is not ideal as there is a lot of overhand. Normally with that type of stern gear the propeller is closer to the stern tube - about 15mm gap. If an anode is needed then one is mounted cclose by on the hull and bonded to the shaft, usually tthrough the gearbox. A shaft anode is meant for boats with a P bracket and exposed shaft between it and the hull.

 

[Crinan12]

I could well be you could do without it. What propeller is it? and does the anode erode? That arrangement is not ideal as there is a lot of overhand. Normally with that type of stern gear the propeller is closer to the stern tube - about 15mm gap. If an anode is needed then one is mounted cclose by on the hull and bonded to the shaft, usually tthrough the gearbox. A shaft anode is meant for boats with a P bracket and exposed shaft between it and the hull.

It's a bronze propellor. Yeah the anode does wear away, lasts 2 seasons. The supplier of the propellor and shaft said an anode was required, they said a lot of boat owners just fit them anyway though.

I have a hull anode as well, a wire goes from it to the stern tube and another one to the engine.

I wasn't sure what the one to the engine was actually doing as my beta engine has a pencil anode. The hull anode doesn't really seem to wear much at all.

Thanks

 

[vyv_cox]

It's a bronze propellor. Yeah the anode does wear away, lasts 2 seasons. The supplier of the propellor and shaft said an anode was required, they said a lot of boat owners just fit them anyway though.

I have a hull anode as well, a wire goes from it to the stern tube and another one to the engine.

I wasn't sure what the one to the engine was actually doing as my beta engine has a pencil anode. The hull anode doesn't really seem to wear much at all.

Thanks

An engine cannot be protected by an external anode. The anode must be in line of sight of the object being protected. It is unlikely that the anode can 'see' the stern tube, in which case your hull anode is doing nothing. My own boat had the same arrangement, plus a wire to the P-bracket, when I bought it in 1994. I removed the anode and filled the bolt holes.

 

[Crinan12]

Thanks.Do you think my hull anode has just been wired to my engine and stern tube because it was installed by someone that wasn't sure what they were doing?

Would have there ever been any point in it do you think?

The boat yard manager said it should be wires to my bronze sea cocks- but I looked into that and that sounds wrong.

 

[Tranona]

It's a bronze propellor. Yeah the anode does wear away, lasts 2 seasons. The supplier of the propellor and shaft said an anode was required, they said a lot of boat owners just fit them anyway though.

I have a hull anode as well, a wire goes from it to the stern tube and another one to the engine.

I wasn't sure what the one to the engine was actually doing as my beta engine has a pencil anode. The hull anode doesn't really seem to wear much at all.

Thanks

The stern tube does not need connecting to an anode. The connection to the engine is based on there being a path to the shaft through the gearbox and the coupling, but may need a bridge over the coupling if it is a flexible type. That is very common on stern gear like yours where a shaft anode is not ideal. However as the shaft anode is eroding then the hull anode is probably not doing anything.

Bronze props on stainless shafts do not need anodes IF they are really bronze. My 1979 boat never had anodes with the original prop. However many props today are actually made of an alloy with zinc and do need anodes.

 

[vyv_cox]

Thanks.Do you think my hull anode has just been wired to my engine and stern tube because it was installed by someone that wasn't sure what they were doing?

Would have there ever been any point in it do you think?

The boat yard manager said it should be wires to my bronze sea cocks- but I looked into that and that sounds wrong.

Yes, that is exactly what I think. Builders and yards seem to install anodes because that's what they have always done, with no thought of the science.

Bonding of seacocks is a case in point. Not only is it impossible for the anode to 'see' all the seacocks but there is good evidence that one seacock can be corroded while protecting another. Look up Random Harvest, a fishing boat sinking. Bonding in USA seems to be more about lightning protection than corrosion.

 

[Tranona]

Thanks.Do you think my hull anode has just been wired to my engine and stern tube because it was installed by someone that wasn't sure what they were doing?

Would have there ever been any point in it do you think?

The boat yard manager said it should be wires to my bronze sea cocks- but I looked into that and that sounds wrong.

Yes. Definitely no need to wire to seacocks in a GRP or wood hull. "Traditional" thinking to attach anodes to any metal underwater without understanding the principles.

 

[Crinan12]

Good to know thanks for the info. My hull anode was on my list to replace but I'll just get rid of it then.

Presumably new fibre glass boats are no longer built with hull anodes. I'm going to have a wander about the yard actually and see how many boats have them out of interest.

 

[Tranona]

Good to know thanks for the info. My hull anode was on my list to replace but I'll just get rid of it then.

Presumably new fibre glass boats are no longer built with hull anodes. I'm going to have a wander about the yard actually and see how many boats have them out of interest.

It varies. Many modern boats have saildrives which have their own anodes. With shaft drives, if they have P brackets then shaft anodes, if stern tubes then commonly prop anodes on the back of the shaft. Folding and feathering propellers usually have their own anodes. More recently small hull anodes have been used as grounds for the 240v system. You will no doubt see many boats with hull anodes because that is the "conventional" way of protecting a propeller. Does not mean of course that they are always used correctly!

 

[RD60]

About to fit new shaft anodes (zinc) and notice a big variation in prices.
Is there any merit in fitting 2 anodes per shaft rather than just one?

 

[colind3782]

About to fit new shaft anodes (zinc) and notice a big variation in prices.
Is there any merit in fitting 2 anodes per shaft rather than just one?

That’s what I do and they last longer.

 

[vyv_cox]

About to fit new shaft anodes (zinc) and notice a big variation in prices.
Is there any merit in fitting 2 anodes per shaft rather than just one?

Painting the prop will double anode life by reducing the size of the cathode.

 

[Graham376]

An engine cannot be protected by an external anode. The anode must be in line of sight of the object being protected. It is unlikely that the anode can 'see' the stern tube, in which case your hull anode is doing nothing. My own boat had the same arrangement, plus a wire to the P-bracket, when I bought it in 1994. I removed the anode and filled the bolt holes.

We have a hull anode connected to the engine and shaft via bridge wire plus the P bracket and rudder bottom bearing, it lasts a couple of years. My shaft also has an anode which lasts about the same. The Featherstream prop anode now lasts about 3 years since using a shaft one.
As the hull anode is obviously working, I see no point in removing it.