Do i really need a prop shaft anode?

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Crinan12

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I've always fitted a prop shaft anode. Never really been sure if I actually needed one or not.

The only reason I would need to lift my boat this year is to replace the anode. If I knew for sure i didn't need an anode I would just lift next year.

I have a stainless steel shaft and bronze prop (details attached).

Can anyone say for sure if I need an anode or not?

Thanks
 

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you have dissimilar metals so likely the answer is yes. How quickly does it erode / disappear? It is unlikely that you have to change it every year but your past experience of the boat is very relevant (and absent in your post). If there are some maintenance posts near you this is an easy job for one tidal cycle.
 
There is galvanic potential between the propeller and shaft due to their differing metallurgies. Left without protection the propeller will corrode in trying to protect the shaft. Introducing an anode causes it to corrode instead of the propeller (and shaft).

There is nearly half a volt between 300 series stainless steel and most copper alloys, which is a significant corrosion risk. So yes, an anode is needed.

A good way to extend the life of the anode is to paint the propeller, reducing the size of the cathode. My anode life doubled after painting my Bruntons prop. See Propeller antifouling with Velox
 
See my post on “prop moths”. No shaft anodes, and a fault on the internal bonding, caused both my prop a rope cutter to be wrecked. So a bill of circa £2500 compared to the cost of a shaft anode. No contest.
 
Thanks. At least I know I need to change it. My boat is at Crinan and I don't think there is anywhere around there to dry out so I'll just go to ardfern and lift it.

I usually replace the anode every 2nd year.
 
vyv_cox said:
There is galvanic potential between the propeller and shaft due to their differing metallurgies. Left without protection the propeller will corrode in trying to protect the shaft. Introducing an anode causes it to corrode instead of the propeller (and shaft).

There is nearly half a volt between 300 series stainless steel and most copper alloys, which is a significant corrosion risk. So yes, an anode is needed.

A good way to extend the life of the anode is to paint the propeller, reducing the size of the cathode. My anode life doubled after painting my Bruntons prop. See Propeller antifouling with Velox
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Thanks. I'll give the painting a go this time as well.
 
Crinan12 said:
I've always fitted a prop shaft anode. Never really been sure if I actually needed one or not.

The only reason I would need to lift my boat this year is to replace the anode. If I knew for sure i didn't need an anode I would just lift next year.

I have a stainless steel shaft and bronze prop (details attached).

Can anyone say for sure if I need an anode or not?

Thanks
Click to expand...
There is no room on our shaft for one, so since 2008 there has never been a shaft anode. The rope cutter takes preference.

Just hauled out and done the underwater prep, bronze prop, S/S shaft, rope cutter and shaft all perfect. Not bad for 17 years with no shaft anode.
 
rotrax said:
There is no room on our shaft for one, so since 2008 there has never been a shaft anode. The rope cutter takes preference.

Just hauled out and done the underwater prep, bronze prop, S/S shaft, rope cutter and shaft all perfect. Not bad for 17 years with no shaft anode.
Click to expand...
Do you have a hull anode? Shaft anodes are only one way of protecting the propeller, and mostly only relevant on boats with P brackets which have an exposed length of shaft where the anodes can be mounted. With "conventional" stern gear there is usually no real exposed shaft - just enough 15-20mm) to let water in and out. If a rope cutter is fitted there is still a need for this gap.
 
Having a long keel often means no room for a shaft anode. I disconnected my flexible shaft coupling which had wires across it and neglected to reconnect them.
Some time later i dried out and discovered how bad my prop had become... i already needed a new shaft as it was very badly worn due to a loose cutlass bearing insert.
New prop and shaft (20 yrs ago) and remade the electrical connection across the uj joint and today the prop is still good so from my experience a shaft anode is not needed.
A friend has a carbon brush set up on his shaft which connects to whatever...
 
Rappey said:
Having a long keel often means no room for a shaft anode. I disconnected my flexible shaft coupling which had wires across it and neglected to reconnect them.
Some time later i dried out and discovered how bad my prop had become... i already needed a new shaft as it was very badly worn due to a loose cutlass bearing insert.
New prop and shaft (20 yrs ago) and remade the electrical connection across the uj joint and today the prop is still good so from my experience a shaft anode is not needed.
A friend has a carbon brush set up on his shaft which connects to whatever...
Click to expand...
Your account suggests that the prop is obtaining protection from somewhere else. Shaft anodes are not always a possibility as you say, but as Tranona points out, there are other options. Do you have a hull anode?
 
vyv_cox said:
Do you have a hull anode?
Click to expand...
I have two of the large mcduff type under the stern. They last a good 3 to 4 years. The prop is electrically connected via the engine and probably to the anode due to all the steel within the hull.
 
Rappey said:
I have two of the large mcduff type under the stern. They last a good 3 to 4 years. The prop is electrically connected via the engine and probably to the anode due to all the steel within the hull.
Click to expand...
That is a common way to protect propellers. Hull anode placed close to the pro and bonded via the engine/gearbox to the shaft with the all importantly wire bridge over the flexible coupling. The latest R&D couplings have a bridge built in. What does the other anode do? Normally no need for more than one.
 
I found the prop anode fell off before a year was up , so painted the prop and installed a hull anode with crossover wire , it's connected to the block and the gearbox.
 
Nothing to add apart from a yes, I have one and it lasts 4 years (kept in the Canal which is fresh water, and due to change next season.

@Crinan12 How’s things as haven’t seen you for few years?
 
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Crinan12 said:
I've always fitted a prop shaft anode. Never really been sure if I actually needed one or not.

The only reason I would need to lift my boat this year is to replace the anode. If I knew for sure i didn't need an anode I would just lift next year.

I have a stainless steel shaft and bronze prop (details attached).

Can anyone say for sure if I need an anode or not?

Thanks
Click to expand...
When you say that you're at Crinan, is that in the fresh water of the canal, or outside in the salt water? I imagine that would make a big difference.
 
My 2p's worth as above no room for a shaft annode , duff teardrop hull anode, crude home made crossover on the uj and all fine for 5 years so far.
 
billyfish said:
I found the prop anode fell off before a year was up , so painted the prop and installed a hull anode with crossover wire , it's connected to the block and the gearbox.
Click to expand...
careful application of some paint or hard antifoul around the securing bolt points (which are invariably the thinnest part of the anode) will enhance their life considerably and have little effect on their performance
 
ctva said:
Nothing to add apart from a yes, I have one and it lasts 4 years (kept in the Canal which iOS fresh water, and due to change next season.

@Crinan12 How’s things as haven’t seen you for few years?
Click to expand...
Yeah all fine chris thanks - we'll pop in to bellanoch to say hi next time we see you. Hope you and Tracey are good.
 
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