Good or Bad: Electro Eliminator for Shaft

[Tranona]

Mmmm, think I will look at putting some additional zinc on the nuts.

That is a good idea. They will waste first because they will be closer to the propellers. However you may well find that if you have a high quality prop (with less zinc than is common in cheaper props) the wastage may be low. Only way to find out is to put it in the water.

 

[Hurricane]

We had this conversation a couple of months ago.
I am not in agreement with Tranona on this subject.
IMHO, shaft anodes confuse the situation.
For me, the idea is to actually "create" a circuit and make the galvanic process work.
So, for me, that means ONE anode and ONE cathode in the circuit.
Then electrically connect them all together.
Thats how my system works - my props are 36 inches dia connected to Stainless Steel shafts and those "brushes" (properly fitted) electrically connecting them to the ships ground bonding.
After 14 years, there is absolutely no sign of corrosion.
Having a shaft anodes halfway up the shafts must change the voltages of that circuit.

Since our discussion a couple of months ago, a friend lifted his sailing boat to find that his expensive folding prop is "badly pitted".
He fits shaft and prop anodes.
He is very cross and blaming other boats berthed around him.
IMO, his system is flawed - I believe that he needs to create a good voltage between his anode and cathode and putting extra anodes in the circuit just reduces the overall galvanic voltage.

Sorry - thats what I believe and it works for me - I would hate to have to replace our props!!!

 

[Tranona]

Of course your system works - but so do others. Shaft anodes are widely used in a variety of applications, particularly where there is nothing else to protect on the boat. The principle of using anodes is to identify the item you wish to protect and site a sacrificial anode as close as possible with the strongest electrical connection. To protect a propeller from the stainless shaft it is mounted on a shaft or prop nut anode is the most suitable approach as these are clamped directly to the metal rather than relying on wires and connections as well as being as close as you can get. The same principle applies to saildrives and outdrives where the aluminium needs protecting from the stainless components. Their anodes are bolted directly to the housing. As I suggested the possible downsides of shaft and nut anodes are possible effects on performance and lack of bulk.

Protection on a boat like yours (and most big mobos) is very different from smaller boats because of the large size of the lumps of metal involved and bonding to a hull anode is the more effective way because of the increase in bulk of the hull anode. The downside is ensuring that the connections of the wiring to complete the circuit are sound and the electro eliminator is a good way of doing this. However on many boats, particularly smaller ones with smaller stern gear the issues are different. My "new" (1979!) boat has no anodes on the stern gear and has been like that from new and there is no sign of corrosion on the prop (1 3/8" shaft and 17" prop). However I am changing the stern gear and fitting a feathering propeller and this will have anodes because it is a mixture of stainless (blades and gears) and bronze body on a stainless shaft. If I was fitting a fixed blade prop I would not add anodes. My last boat with a saildrive and bronze folding prop only had the saildrive anode and despite being in the water all year round I only changed that once in the 6 years I had it.

There is a huge amount of misunderstanding about the use of anodes and many boats are festooned with totally unnecessary anodes and bonding. For example my new boat has anodes on the sheet steel bilge plates and amazingly on the 316 stainless bottom rudder fitting. All totally unnecessary, shown by the fact that they are almost unwasted despite having been there for at least 15 years! The other misconception is bonding through hulls and seacocks in a GRP or wooden boat. In most cases unnecessary because they are not connected electrically to anything else, and in the case of wooden boats they often lead to a chemical reaction with the wood. When I installed a hull anode in my wooden boat I lined the holes with epoxy, although in fact once I found out more about the use of anodes I removed it completely as the propeller had its own anode and the bonding to the stern tube had started to cause decay in the horn timber. (Useful spending time with a good wooden boat surveyor!)

Just to be clear given what prompted this thread metal boats, steel or aluminium are very different from GRP and require different strategies, although often the shaft/prop issues are the same because they are usually electrically isolated from the hull and machinery.

 

[Surfacesub]

="Plum, post: 7946083, member: 169"]
I have that arrangement too but the electrical resistance from gearbox to shaft is excessively high so had to fit a Electro Eliminator.

www.solocoastalsailing.co.uk
[/QUOTE]
Did fitting the Electro Eliminator make much difference?

 

[Surfacesub]

I have that arrangement too but the electrical resistance from gearbox to shaft is excessively high so had to fit a Electro Eliminator.

www.solocoastalsailing.co.uk

Did fitting the Electro Eliminator make much difference?

 

[Plum]

Did fitting the Electro Eliminator make much difference?

Yes, reduced the resistance from over 1000 ohms to 10 ohms. Idealy it should be less than 1ohm. I will have another go at cleaning the contact between the brushes and the shaft as I am nearly there!

Www.solocoastalsailing.co.uk

 

[Portofino]

Both systems work it depends on the major engine protection that dictates which way the builder goes .
MANs mine and Barts do not use cooler anodes .There are zero anodes hidden out of sight on engine components .
The engines are -ve isolated from the boats other D.C. systems.

So how do they protect themselves?

They use a huge transom anode ( could be anywhere on the hull ) which is bonded by what looks like a church lightening conductor copper strip .This runs the L of the ER above the bilge .Anything can be attached , seacocks , tanks , exhausts what have you .In my boat the ancillary’s wires are those green / yellow striped Earth wires you find in a house .
Eg the metal faucets where the underwater exhaust go through the hull are “ earthed “ to the transom’s anode .
Inside the transom the steering gear , rudders etc even my aircon pumps are connected in after all they carry seawater in the circuit .

So with the shafts + props they are as said mechanically connected indirectly via the gear box to the engines to the transom anode via the two copper trips ……along with anything else .
Additionally the mass of zinc , the anodes is increased with the nose anodes on the props themselves, the flap anodes and there are some anodes on the metal bathing platform ( not shown in the pics ) Estimate about 12kg of zinc within a 1M of the props .
Over a kilo + directly attached .
The 80 mm SS shafts have no anodes to interfere with water flow to the cutlass bearings .Remember they are attached to the engine so the hull anodes .

As far as depletion, the rate it’s never bang on 12/12 .With a med boat + snorkel ( actually a mimi dive bottle ) I can change them as and when .
Yes other boats in a marina can and do influence them depletion rate and yes before winter ( end of OCT ) I have been known to replace one or two before leaving it until May / June so they have sufficient mass to get through the winter .

The beauty of is I know the engines , props and shafts are protected the pricy bits . I can eye ball the zincs and respond to depletion if necessary.

I guess if your boats motors are littered with pencil anodes out of sight , out of mind the builder mat want to separately beef up shaft / prop protection use electro elimination.After all in big boats the shafts are directly connected , no rubber vibration damper between shaft + gearbox is gonna cope with torque numbers ending well into in 4 figures .
You see you don’t want your tiny cooler anodes to deplete try to protect the shafts / props do you .

The downer is the brushes grease up , get dirty and contact is diminished = the cooler anodes get beaten up , out of sight .
As mentioned by Tarona ^^^ at the end of the day , it’s sheer mass of Zn about as close as if not attached to the thing(s) you want to protect .You just don’t know what other boats or marina structures are up to nearby in the marina from a anode / cathode pov .

I read some where some guys over wintering scrounge old zincs and hang them from the stern of there bathing platforms bonding them to the system(s) ….to just as said bulk up the zinc mass .

For me it’s just reassuring to see prop anodes and transom anodes every time I go swimming ( Med useage ) .
Thats virtually daily.


Don’t worry guys I replaced the depleted anode ^
Thats the point .I can see they are working .