S34 Galvanic Protection

K

kalanka

Well-Known Member
Joined
21 Jan 2005
Messages
273
Location
North West Scotland
Visit site
Sadler 34 1988. There is a stud inside the hull near to the seawater intake that is the connection point for the wires connecting the skeg, gearbox etc for anti-corrosion purposes. I have just noticed that the other end of the stud appears to be flush with the hull on the outside.

Is this part of the arrangement? Does it need to be exposed so as to be in contact with seawater or can I cover it with epoxy or anti foul? Should it have a sacrificial anode on the outside? There are anodes on the prop shaft and on the keel.

Thanks
 
No takers on this one all evening, so will bump it up and post something for others to disagree with

Must admit to being puzzled

The stern gear is protected by the shaft anode........ unusual to have anodes on the keel.

As you describe it the wiring to skeg and gearbox is doing nothing if not connected to an anode..... Concerned though by what you may be meaning by "etc", not skin fittings I hope.

The only suggestion I can make is that there was a hull anode at one time, but they usually have two studs.

If the stud is flush with the outside of the hull what is holding it in place ?
 
There must be an anode on the outside otherwise you will quickly find the stud eroding away and a hole in the bottom of the boat. I had a very similar situation last year and only just lifted out of the water in time.

Yoda
 
DavidBolger said:
I have a Sadler 34 and there should be an anode on the exterior of the hull.
Click to expand...

+1

I used to have a Sadler 34 of 87/88 vintage and she had a stud just where Kalanka says. It was there to secure a 'doughnut' anode on the outside of the hull and to provide a terminal for the wires running in the bilge to the anode. Possibly Kalanka yours is the stud remaining after the anode has gone and it has been tightened up to neaten it or a previous owner had the original fixing bolt replaced with a short one. Either way I think you need the anode and as you have the wiring already in place the obvious thing to do is replace the anode and use the existing bolt or a longer one if necessary.

Once you've fitted the anode you need to check the integrity of the circuit between the anode and the other underwater metalwork, but I guess you know that already.

Incidentally I didn't have a keel anode. One thing I learned about Sadlers was that what I saw on one didn't necessarily apply to mine as the builders used to do lots of one-offs for special customers (specially where they were buying several boats), and they went bust and reopened. And 25 years is long enough for owners to make plenty of modifications to the original boat.

Having said all that, my Sadler was a great boat and gave me lots of fun and taught me a lot . . .
 
jbweston said:
+1

I used to have a Sadler 34 of 87/88 vintage and she had a stud just where Kalanka says. It was there to secure a 'doughnut' anode on the outside of the hull and to provide a terminal for the wires running in the bilge to the anode. Possibly Kalanka yours is the stud remaining after the anode has gone and it has been tightened up to neaten it or a previous owner had the original fixing bolt replaced with a short one. Either way I think you need the anode and as you have the wiring already in place the obvious thing to do is replace the anode and use the existing bolt or a longer one if necessary.

Once you've fitted the anode you need to check the integrity of the circuit between the anode and the other underwater metalwork, but I guess you know that already.

Incidentally I didn't have a keel anode. One thing I learned about Sadlers was that what I saw on one didn't necessarily apply to mine as the builders used to do lots of one-offs for special customers (specially where they were buying several boats), and they went bust and reopened. And 25 years is long enough for owners to make plenty of modifications to the original boat.

Having said all that, my Sadler was a great boat and gave me lots of fun and taught me a lot . .
Click to expand...

Why?
 
VicS said:
Why?
Click to expand...
A little grumpy this morning, are we, VicS?

Assuming you aren't just trolling . . .

Because:
1. He has wires going to a stud which might well corrode away instead of the non-existent anode (depending on what metals he's got underwater), always assuming the bolt is wired up in the bilge to other underwater metalwork - thus leaving a nasty bolt size underwater hole in the hull.

2. The boat was designed and built to have galvanic protection and if some earlier owner was relying on the other keel anode it looks as if he didn't know what he was doing as he hasn't bothered to remove the bolt and wiring in question. Anyway we don't know how/if the keel anode is wired properly.

3. I belong to the school of thought that isn't impressed with the 'no anodes' approach. I prefer my bronze skin fittings and sterngear to last more than a season and a half! But perhaps this isn't the place to argue about whether boats need galvanic protection . . .

4. Using the existing bolt appeals to my sense of neatness where a boat has everything in its place.
 
My Sadler 34 had an anode on the port side in the engine compartment. It had clearly been fitted poorly by a previous owner. It was connected to the P-bracket and to the engine seawater skin fitting, which the anode could not 'see' as it is on the starboard side. I removed the anode as one of the first jobs I ever did on the boat, before we launched for the first time. That was getting on for 20 years ago. All my skin fittings and seacocks are the same ones that were fitted when I bought the boat, with the exception of the P-bracket that was damaged. I have epoxy coated that to avoid dezincification.
 
jbweston said:
A little grumpy this morning, are we, VicS?

Assuming you aren't just trolling . . .

Because:
1. He has wires going to a stud which might well corrode away instead of the non-existent anode (depending on what metals he's got underwater), always assuming the bolt is wired up in the bilge to other underwater metalwork - thus leaving a nasty bolt size underwater hole in the hull.

2. The boat was designed and built to have galvanic protection and if some earlier owner was relying on the other keel anode it looks as if he didn't know what he was doing as he hasn't bothered to remove the bolt and wiring in question. Anyway we don't know how/if the keel anode is wired properly.

3. I belong to the school of thought that isn't impressed with the 'no anodes' approach. I prefer my bronze skin fittings and sterngear to last more than a season and a half! But perhaps this isn't the place to argue about whether boats need galvanic protection . . .

4. Using the existing bolt appeals to my sense of neatness where a boat has everything in its place.
Click to expand...

Just because a boat is fitted with an anode either by the builder or a subsequent owner does not mean it needs one. Not sure where you get the idea that "underwater fittings" will only last a season and a half without one. If they are made from the correct material (bronze or DZR) as the vast majority are, they do not need anodic protection. Seacocks are not in contact with any other metal (in a GRP boat) so there cannot suffer from any galvanic action. If they are corroding then it is usually dezincification because they are brass and not the more common DZR.

The only parts that may require anodic protection are in the stern gear, particularly the prop which is in contact with the stainless steel shaft and possibly a rudder if it is made of mixed metals. The prop can be protected by a hull anode mounted in sight of the prop and bonded to the shaft/prop assembly, usually through the gearbox, or a shaft anode. There is no point normally in putting an anode on a cast iron keel as there is no possibility of galvanic action. Any corrosion of the keel is usually old fashioned rust.

So, the answer to the OP is that he may need a hull anode for the stern gear if the shaft anode is insufficient. It does not need to be connected to anything else.
 
Agree with both vyv_cox and Tranona. I fact I have a friend with a Ben 50 that had a total of 14 sea cocks. He was told that he must connect all of then together and to an anode. After 3 month his sea cocks started to get a white growth which had not happened in the previous 12 months. He then disconnected and cleaned the fittings and in the next 4 years had no problem.

I think the fittings of anodes unnecessary was due to lack of knowledge/miss understanding and/up the promotion of anodes by the anode manufactures.

IMHO anodes are only needed where different metals are electrically connected or metal hulled boats. On my steel boat I have steel hull with stainless steel sea cocks and prop shaft. The only other metal I have is a bronze prop and bow thruster gear box.

The last time I inspected my anodes (6 month ago) there was a small amount of erosion on the hull anodes (after 3 1/2 years) and on the prop shaft anodes. The erosion on these prop shaft anodes are about twice the hull anodes and may need changing next year but I have fitted a fabricated stainless steel prop so will see what effect this has on the prop shaft anodes next year.
 
jbweston said:
A little grumpy this morning, are we, VicS?

Assuming you aren't just trolling . . .

Because:
1. He has wires going to a stud which might well corrode away instead of the non-existent anode (depending on what metals he's got underwater), always assuming the bolt is wired up in the bilge to other underwater metalwork - thus leaving a nasty bolt size underwater hole in the hull.

2. The boat was designed and built to have galvanic protection and if some earlier owner was relying on the other keel anode it looks as if he didn't know what he was doing as he hasn't bothered to remove the bolt and wiring in question. Anyway we don't know how/if the keel anode is wired properly.

3. I belong to the school of thought that isn't impressed with the 'no anodes' approach. I prefer my bronze skin fittings and sterngear to last more than a season and a half! But perhaps this isn't the place to argue about whether boats need galvanic protection . . .

4. Using the existing bolt appeals to my sense of neatness where a boat has everything in its place.
Click to expand...

Grumpy? No more than normal for 0800 GMT

Trolling? No. Wondering what reasons you have for thinking that the OP needs a hull anode.

Its a strange idea that the boat has been designed to have cathodic protection... It may have been built using components made of materials that are not corrosion resistant and therefore needs cathodic protection as a consequence but the OP mentions no corrosion problems without the hull anode that would lead to that conclusion.
 
Well, kalanka, there you have it.

A choice of opinion from people of varying degrees of expertise, both real and claimed, and varying amounts of dogmatism.

Personally, if I had your boat I'd put an anode on and wire it back to the engine block (which I hope is where your existing wires go), test the circuit with a meter and then rest easy because if there's electrolytic action, you're sterngear is covered, and if there isn't you'll see a pristine anode at the end of the season. I never saw my anode pristine and she'd had the start of some dezincification of the cooling water inlet in the previous ownership which is why I think it's a sensible investment of time and money to fit one, particularly where it has been thought necessary in the past.

Talk of wiring the anode back to seacocks that are electrically isolated is a red herring - no sensible person is going to advise that. It's the sterngear and engine (and any through-hull fittings that are electrically connected) that you are protecting or not, depending on whose line you follow.

I think I'll steer clear of anode threads in future as plainly the subject is a bit of a red rag. Like anchor threads, it's hard to tell if the vehemence of opinion bears any correlation to the the knowledge of the poster. But beware the anode police, because it does seem that fitting an anode is a serious misdemeanour in their book. You could always fit one and keep it a secret from them, I suppose . . .
 
jbweston said:
Well, kalanka, there you have it.

A choice of opinion from people of varying degrees of expertise, both real and claimed, and varying amounts of dogmatism.

Personally, if I had your boat I'd put an anode on and wire it back to the engine block (which I hope is where your existing wires go), test the circuit with a meter and then rest easy because if there's electrolytic action, you're sterngear is covered, and if there isn't you'll see a pristine anode at the end of the season. I never saw my anode pristine and she'd had the start of some dezincification of the cooling water inlet in the previous ownership which is why I think it's a sensible investment of time and money to fit one, particularly where it has been thought necessary in the past.

Talk of wiring the anode back to seacocks that are electrically isolated is a red herring - no sensible person is going to advise that. It's the sterngear and engine (and any through-hull fittings that are electrically connected) that you are protecting or not, depending on whose line you follow.

I think I'll steer clear of anode threads in future as plainly the subject is a bit of a red rag. Like anchor threads, it's hard to tell if the vehemence of opinion bears any correlation to the the knowledge of the poster. But beware the anode police, because it does seem that fitting an anode is a serious misdemeanour in their book. You could always fit one and keep it a secret from them, I suppose . . .
Click to expand...

It is not dogmatism, nor a red herring. If a seawater inlet is dezincifying it is probably because it is brass, not because of galvanic action and being wired to an anode won't stop it.

The vast majority of boats do not have their seacocks connected to an anode and do not have problems if the fittings are made of DZR or bronze.

Connecting to the engine block per se is potentially ineffective as there is nothing in the engine to protect except possibly in a heat exchanger when the engine has its own anode. The connection is required to the shaft and prop and this is often done by using the gearbox as a pathway. However, this becomes ineffective if there is a flexible coupling which will then need a bridge. That is why shaft anodes are popular because there is a direct electrical connection to the prop.

Suggest you read up on galvanic corrosion and the material on the MG Duff website to gain a better understanding of the subject. You may also find Vyv Cox's website (see his earlier post) useful.
 
Perhaps one or two of us need to lighten up a bit and not behave as though they are the founts of all knowledge and everyone else some sort of educationally challenged ignoramus in need of a good lecturing at?

It must be a whole load of fun sharing a long night watch with some of you . . .

Why not get back to advising kalanka what to do with his anode bolt and wires rather than trying to prove how much more you know than I do. It's just rude and must give people new to the forum the impression that sailors are all arrogant know-it-alls. We aren't. Really we aren't. Many of us are quite nice guys . . .
 
I've often wondered what purpose the hull anode serves on our boat. It's wired to the common earth - engine - but not to anything else. The 230v mains earth isn't connected to the 12v neg so what's the purpose of the hull anode? The steel rudder has two disc anodes and the shaft has a ring anode.
 
kalanka said:
Sadler 34 1988. There is a stud inside the hull near to the seawater intake that is the connection point for the wires connecting the skeg, gearbox etc for anti-corrosion purposes. I have just noticed that the other end of the stud appears to be flush with the hull on the outside.

Is this part of the arrangement? Does it need to be exposed so as to be in contact with seawater or can I cover it with epoxy or anti foul? Should it have a sacrificial anode on the outside? There are anodes on the prop shaft and on the keel.

Thanks
Click to expand...

You must do something with that stud ! It is almost certainly the remains of a fixing stud for an anode ..There is probably nothing much holding it in place apart from the old sealant and as it was probably only a zinc plated mild steel stud it will slowly corrode away even if it does not become dislodged.


Personally, and I suspect Vyv might do the same, I would remove it and make good the hole.

If there is any indication of galvanic corrosion that an anode might cure then by all means fit a new anode but remember that items to be protected must be near, "in line of sight of" and properly bonded to the anode.

You could fit an new anode anyway but its another job you will have to add to the list to do as and when it is corroded away

Please check the other wires on that stud to ensure that there are no connections to through bronze or DZR hull fittings. Do this whether or not you fit an anode
 
Last edited:
jbweston said:
Perhaps one or two of us need to lighten up a bit and not behave as though they are the founts of all knowledge and everyone else some sort of educationally challenged ignoramus in need of a good lecturing at?

It must be a whole load of fun sharing a long night watch with some of you . . .

Why not get back to advising kalanka what to do with his anode bolt and wires rather than trying to prove how much more you know than I do. It's just rude and must give people new to the forum the impression that sailors are all arrogant know-it-alls. We aren't. Really we aren't. Many of us are quite nice guys . . .
Click to expand...

Suggest you reread your previous post before you make judgements. What you have been saying is mostly incorrect or misleading and one or two people have made polite suggestions as to why and where you can get more information on the subject from both theoretical and practical perspectives.

Kalanka has received good advice by several people - not surprisingly all the same, and different from yours, about what he might do.
 
Lazy Kipper said:
I've often wondered what purpose the hull anode serves on our boat. It's wired to the common earth - engine - but not to anything else. The 230v mains earth isn't connected to the 12v neg so what's the purpose of the hull anode? The steel rudder has two disc anodes and the shaft has a ring anode.
Click to expand...

It has been probably fitted to protect the stern gear ....... any flexible coupling in the shaft should also have been bridged to ensure a circuit all the way. With a shaft anode it should not be necessary ...... in fact if you have a decent manganese bronze prop the shaft anode is probably not doing anything useful either!

I hope you have an RCD in the incoming shorepower connection.
 
Lazy Kipper said:
I've often wondered what purpose the hull anode serves on our boat. It's wired to the common earth - engine - but not to anything else. The 230v mains earth isn't connected to the 12v neg so what's the purpose of the hull anode? The steel rudder has two disc anodes and the shaft has a ring anode.
Click to expand...

The hull anode is probably intended to protect the prop via the gearbox. I expect the bonding wire is to a bell housing bolt as this is usually the most convenient. It relies on there being a good electrical path to the shaft/prop, but as I suggested earlier it may be compromised if you have a flexible coupling. The shaft anode is doing the most work being firmly attached to the shaft and near the prop. So even if the hull anode is well bonded you may find it does little while the shaft anode is active.

As has been suggested earlier it is not unusual for anodes to be stuck on the boat without fully understanding their purpose and how they should be connected.

The anodes on the rudder may also do little. They are usually fitted if the rudder is galvanised and/or it has non ferrous fittings such as a steering quadrant or runs in bronze bearings. No harm in leaving them there and replacing if they do erode.
 
You must log in or register to reply here.

Share this page

Top