Hull Anode?

[Quandary]

Another question, hope I am not boring you but I respect the advice and enjoy the dialogue.
Our Moody with a saildrive and a fresh water cooled engine, VP2020, has anodes on the leg and on the prop. (at present I am using aluminium because the boat stays in fresh water).
I have been told I need to fit a hull anode but not why. I always assumed an anode had to protect something, but the only external metal is protected and the engine only has sea water as far as the heat exchanger which is mainly expelled by the exhaust. There is one bronze skin fitting just above water level discharging both sinks and another buried in the hull layup for the head, do I perhaps need to wire this external anode to those?
The easy thing is just to fit one rather than argue but not if it has no purpose.

 

[pvb]

If the saildrive and prop have their own anodes, there's no need for a hull anode. You certainly don't need to wire bronze skin fittings to an anode.

Some boats have a hull anode as an earthing point for electrical installations.

 

[PaulRainbow]

I'd ask the person that told you to fit the hull anode "what should i connect to the anode" ?

In days of olde through hull fitting were often wired to anodes, but this is now considered not necessary, in fact, it's a bad idea.

If your shore power installation needs to be earthed to the water, then a hull anode can be used for this. If an inverter is fitted it will require a connection to the water, a hull anode can be used here too. If your shore power is currently not connected to the water and you don't plan to fit an inverter i cannot see any reason to fit a hull anode.

EDIT: Typed while PVB was posting

 

[vyv_cox]

My boat had a hull anode wired to the P-bracket. Complete waste of effort, as an anode cannot protect from dezincification and there is no other likelihood of corrosion. I took it off.

 

[Quandary]

The person who asked for it is a professional, I was using this question to help establish his level of expertise.
To be fair to him he may just be behind the times, long after Moody started using saildrives they were still fitting hull anodes, but that was toward the end of the last century, they were still adding fore and aft lowers to masts with twin swept speaders too, even to fractional rigs, old habits die hard.

Thanks to you guys for taking the time to respond, I have confidence in each of you.

 

[PaulRainbow]

The person who asked for it is a professional, I was using this question to help establish his level of expertise.
To be fair to him he may just be behind the times, long after Moody started using saildrives they were still fitting hull anodes, but that was toward the end of the last century, they were still adding fore and aft lowers to masts with twin swept speaders too, even to fractional rigs, old habits die hard.

Thanks to you guys for taking the time to respond, I have confidence in each of you.

Without knowing why he thinks you need a hull anode, you cannot tell anything.

 

[Bodach na mara]

Interesting thread. I also had this problem when I bought my last boat in 1997. The surveyor noted that there was no anode and one of the recommendations was that one should be fitted and connected to the engine block, stern gear, rudder stock and tube and all seacocks should be bonded to it. I asked whether the cast steel keel should also be bonded and was told not to as if I wanted the keel protected I should mount a separate anode directly onto it which I didn't, as it had not been mentioned in the survey report. The only reason I fitted one at all was that the insurance company required me to certify that 'all surveyor's recommendations have been followed".

So as the anode on Sea Hawk is now at renewal level and it seems to be bonded only to seacocks is it now better to remove it and all the bonding wires?

 

[PaulRainbow]

Interesting thread. I also had this problem when I bought my last boat in 1997. The surveyor noted that there was no anode and one of the recommendations was that one should be fitted and connected to the engine block, stern gear, rudder stock and tube and all seacocks should be bonded to it. I asked whether the cast steel keel should also be bonded and was told not to as if I wanted the keel protected I should mount a separate anode directly onto it which I didn't, as it had not been mentioned in the survey report. The only reason I fitted one at all was that the insurance company required me to certify that 'all surveyor's recommendations have been followed".

So as the anode on Sea Hawk is now at renewal level and it seems to be bonded only to seacocks is it now better to remove it and all the bonding wires?

I would remove all bonding wires to the rudder stock and tube and all seacocks.

Is the boat shaft drive or sail drive ?

Is there a shore power earth cable going to the anode ?

Is there an inverter (or are you likely to fit one)?

 

[Bodach na mara]

Thanks Paul, I will need to check whether the shore power is earthed to it. The drive is via a shaft through a Volvo Penta lip seal and the only inverter on board is a small one with a single 13 amp socket outlet that is connected to the battery with crock clips when required.

 

[PaulRainbow]

Thanks Paul, I will need to check whether the shore power is earthed to it. The drive is via a shaft through a Volvo Penta lip seal and the only inverter on board is a small one with a single 13 amp socket outlet that is connected to the battery with crock clips when required.

I would replace the anode, but remove the bonding wires as per post #8. Leave the wire connected to the gearbox, if the shaft coupling is solid it will be a backup for any shaft/prop anodes (if fitted ?), if it's a flexible coupling fit a bridging wire to one bolt on the gearbox side and one on the shaft side.

 

[Moodysailor]

On an alternative train of thought, if I had a boat with a saildrive, I would probably fit a hull anode connected solely to this.

The reason is becuase the S/D anodes are marginal at best and I have seen these eaten away in half a season before now, so the hull anode would simply provide an additional resources to protect the leg & prop.

I would echo the recommendations of others regarding bonding through hulls, rudder tubes, grannys knickers, etc - don't bother.

 

[Quandary]

My experience has been different, the sail drive anode hardly degrades at all, even the aluminium one, while the prop anode is the one that struggles to last two seasons even with the prop painted. I did take quite a bit of care with priming, spraying and then antifouling the leg while it was out for a hull seal change. it included two coats of special metals primer plus several of car paint. I have been using Hempel Ecopower prop. aerosol spray on it each year and am meticulous about touching up any primer or undercoat chips.

 

[vyv_cox]

Interesting thread. I also had this problem when I bought my last boat in 1997. The surveyor noted that there was no anode and one of the recommendations was that one should be fitted and connected to the engine block, stern gear, rudder stock and tube and all seacocks should be bonded to it. I asked whether the cast steel keel should also be bonded and was told not to as if I wanted the keel protected I should mount a separate anode directly onto it which I didn't, as it had not been mentioned in the survey report. The only reason I fitted one at all was that the insurance company required me to certify that 'all surveyor's recommendations have been followed".

So as the anode on Sea Hawk is now at renewal level and it seems to be bonded only to seacocks is it now better to remove it and all the bonding wires?

Surveyors often seem to be confused over bonding seacocks. This is common practice in USA but more for lightning protection than corrosion resistance, particularly since bronze seacocks are almost universal over there.

Bonding can actually cause corrosion, by creating galvanic couples. Apart from that the items being protected need to 'see' the anode, almost always impossible on a hull.

 

[pvb]

On an alternative train of thought, if I had a boat with a saildrive, I would probably fit a hull anode connected solely to this.

The reason is becuase the S/D anodes are marginal at best and I have seen these eaten away in half a season before now, so the hull anode would simply provide an additional resources to protect the leg & prop.

Half a season would seem to indicate something's wrong! My current boat is the first I've had with a saildrive. As I routinely only lift the boat once every 2 years, I was initially cautious about the life of the saildrive anode. However, I lifted in July and the anode - then 4 years old - was still fine, so I refitted it.

If you routinely use shorepower, a galvanic isolator could be beneficial, as well as checking that your saildrive is electrically insulated from the engine.

 

[Tranona]

On an alternative train of thought, if I had a boat with a saildrive, I would probably fit a hull anode connected solely to this.

The reason is becuase the S/D anodes are marginal at best and I have seen these eaten away in half a season before now, so the hull anode would simply provide an additional resources to protect the leg & prop.

I would echo the recommendations of others regarding bonding through hulls, rudder tubes, grannys knickers, etc - don't bother.

While it is true that some saildrive anodes go quickly, particularly the small ones on the old 110 and 120 style legs, many last for years. My first saildrive, a 120 barely wasted in 7 years in the Med and even after reducing the bulk to fit a Stripper did 4 years in the UK. The later 130 and 150 with split anodes have over twice the bulk. My latest 130 was changed after the first 5 years and it was less than half gone by weight.

Unfortunately adding a hull anode does not do much. While a hanging anode has value if you go into fresh water as you can use a magnesium anode directly connected to the saildrive housing inside the boat. However a hull anode, again bonded to the saildrive housing will only come in when the one on the drive is completely gone. The normal anode is direct to the housing and erodes first and then the hull anode, which is further away is "seen" . There is perhaps some value in adding one if the boat has a 120 drive and there are plans to keep it in the water for a long time and it has a history of high wastage. but for normal annual or even biannual haulouts not worth it.

 

[dunedin]

My experience has been different, the sail drive anode hardly degrades at all, even the aluminium one, while the prop anode is the one that struggles to last two seasons even with the prop painted. I did take quite a bit of care with priming, spraying and then antifouling the leg while it was out for a hull seal change. it included two coats of special metals primer plus several of car paint. I have been using Hempel Ecopower prop. aerosol spray on it each year and am meticulous about touching up any primer or undercoat chips.

That’s what we have found - saildrive anode only loses 10% or so in a year, prop anode barely lasts a season.

And no hull anode - so agree with others about the wrong advice

But if selling the boat, surely none of this applies. Sold as seen. If the surveyor wants to suggest to a buyer that they fit an anode (even if bonkers), that is something for them to do post purchase surely. Not for seller to do?

 

[stuartwineberg]

Interesting. From my Moody 36 owners manual (1998)
Craft fitted with standard stern gear are fitted with one hull mounted sacrificial anode, craft fitted with a saildrive unit are fitted with an additional anode mounted on the saildrive leg. The hull mounted anode is wired in circuit to the fuel tank, engine and AC shore support system including the distribution panel and the AC socket earth circuit.

I am no electrical expert so interested in comments. I have fitted a galvanic isolator. The hull anode lasts a season

 

[Moodysailor]

Half a season would seem to indicate something's wrong! My current boat is the first I've had with a saildrive. As I routinely only lift the boat once every 2 years, I was initially cautious about the life of the saildrive anode. However, I lifted in July and the anode - then 4 years old - was still fine, so I refitted it.

If you routinely use shorepower, a galvanic isolator could be beneficial, as well as checking that your saildrive is electrically insulated from the engine.

While it is true that some saildrive anodes go quickly, particularly the small ones on the old 110 and 120 style legs, many last for years. My first saildrive, a 120 barely wasted in 7 years in the Med and even after reducing the bulk to fit a Stripper did 4 years in the UK. The later 130 and 150 with split anodes have over twice the bulk. My latest 130 was changed after the first 5 years and it was less than half gone by weight.

Unfortunately adding a hull anode does not do much. While a hanging anode has value if you go into fresh water as you can use a magnesium anode directly connected to the saildrive housing inside the boat. However a hull anode, again bonded to the saildrive housing will only come in when the one on the drive is completely gone. The normal anode is direct to the housing and erodes first and then the hull anode, which is further away is "seen" . There is perhaps some value in adding one if the boat has a 120 drive and there are plans to keep it in the water for a long time and it has a history of high wastage. but for normal annual or even biannual haulouts not worth it.

Hey, don't shoot - I said I have seen it happen. I worked as a marine engineer for 20+ years, many of those at a VP main dealer (later centre). The areas I worked (UK south coast) were synonymous with anode depletion on sterndrives, and often saildrives.

The hull anodes were something I've seen done in these areas, and I would do the same on my own boat if we have one with a S/D. It does no harm, and provides additional protection to an expensive, underwater aluminium part.

As always, anyone else is free to do what they like with the advice on this forum ??

 

[yotter]

I once made the error of not checking/changing my SD130 anode. On hoisting at the end of a season, I found corrosion on the SD130 where the bearing housing connects, fortunately this was fixable (with good valuable advise from this forum). The takeaway was to check the continuity between anode and saildrive, some horrible white powder had formed where the anode connects to the bearing carrier which I did not see causing a poor electrical contact. The anode lasts quite a while since the propeller is a Kiwi prop and contains very little metal. I have not started to hang an anode over the side when moored, this is connected to a stud on the SD130 gearbox, I consider this as belt and braces.

 

[stuartwineberg]

I would remove all bonding wires to the rudder stock and tube and all seacocks.

Is the boat shaft drive or sail drive ?

Is there a shore power earth cable going to the anode ?

Is there an inverter (or are you likely to fit one)?

Hi Paul
as per my post it seems older Moodys are earthed through the anode. I don’t understand this. Is it good or bad and does it need action?