Anodes ??

[waynes world]

Hi all.

My mate has gone a bought a GRP boat as below



He has had it delievered and the yard check it ver and cleanned it etc etc ands found that the Anodes have all corroded away.

Now he noticed there wasnt any on the prop shaft or rudders.

Would it best to fit some aswell as replace the others in the hull ?

Cheers

Faffer

 

[Tranona]

The ones in the hull will be wired (bonded electrically) to the propellers and the rudders - that is what they are for. The fact that they are wearing is an indication that the bonding is sound. There is a lot of metal there to protect!

His surveyor should have reported on the soundness (or otherwise) of the bonding system as it is pretty important on a boat like that.

 

[waynes world]

The ones in the hull will be wired (bonded electrically) to the propellers and the rudders - that is what they are for. The fact that they are wearing is an indication that the bonding is sound. There is a lot of metal there to protect!

His surveyor should have reported on the soundness (or otherwise) of the bonding system as it is pretty important on a boat like that.

well i have just found he has ordered some more anodes for the props, is it a benefit to fit hem now he as bought them ? Am i correct in thinking that they would last longer if more fitted.

 

[penfold]

They're supposed to erode, without knowing the timescale of the erosion there's no means to decide if there is a problem or not. What are the rudders made of?

 

[waynes world]

They're supposed to erode, without knowing the timescale of the erosion there's no means to decide if there is a problem or not. What are the rudders made of?

yes i know they erode, was wondering if more would be better. i dont know what the rudders are made from.

 

[penfold]

More isn't better; the anodes are sized to protect exposed metal, mainly the shafts.

 

[Tranona]

well i have just found he has ordered some more anodes for the props, is it a benefit to fit hem now he as bought them ? Am i correct in thinking that they would last longer if more fitted.

Not necessarily. I would guess the boat has been around for many years with the current arrangements and if there is no sign of dezincification of the props and rudders then can't see any reason to change. The hull anodes will be located close to the stern gear so that they can "see" the yellow metal they are protecting. You don't say what sort of prop anodes he has ordered - there are 2 types, the most common are those that clamp around the shaft just forward of the P bracket. If these are fitted then they will wear first because they are closer to the props. When they have gone then the hull anodes will take over so overall the combination will give a longer potential life . This may be useful if he wants to extend the interval between lift outs. The second type is attached to the nut, but it needs a special nut and generally not fitted if it is possible to fit a shaft anode.

However rather than just sticking on more anodes, perhaps better to find out if there really is a need. Just replace the ones that are there - normal to replace them if they are 50% down by weight after a normal period in the water between haulout. But if it is not known how long the current ones have lasted replace them with new and, crucially have an electrician check for continuity between the anodes and the props and rudders.

If previous owners have not seen the need to add shaft anodes, then best not to do so now until he has a better understanding of whether there really is a need.

 

[waynes world]

Not necessarily. I would guess the boat has been around for many years with the current arrangements and if there is no sign of dezincification of the props and rudders then can't see any reason to change. The hull anodes will be located close to the stern gear so that they can "see" the yellow metal they are protecting. You don't say what sort of prop anodes he has ordered - there are 2 types, the most common are those that clamp around the shaft just forward of the P bracket. If these are fitted then they will wear first because they are closer to the props. When they have gone then the hull anodes will take over so overall the combination will give a longer potential life . This may be useful if he wants to extend the interval between lift outs. The second type is attached to the nut, but it needs a special nut and generally not fitted if it is possible to fit a shaft anode.

However rather than just sticking on more anodes, perhaps better to find out if there really is a need. Just replace the ones that are there - normal to replace them if they are 50% down by weight after a normal period in the water between haulout. But if it is not known how long the current ones have lasted replace them with new and, crucially have an electrician check for continuity between the anodes and the props and rudders.

If previous owners have not seen the need to add shaft anodes, then best not to do so now until he has a better understanding of whether there really is a need.

Thanks for that info, Ill tell him later. i know he has got the clamp on type anodes ordered though.
He is sort of worrying a bit as this is his first proper boat so wants to be fully prepared as much a she can.

thanks again