Protecting your VP Saildrive from Stray Currents

[Kaptajnen]

While connected to Shore Power, your expensive VP saildrive is exposed to stray currents. The original model 120S saildrive did not have any isolation from the MD22L engine, so a faulty starter or alternator with a short circuit could destroy the saildrive in a few hours.

This happened to our boat and we replaced the saildrive with the improved 130S, which is isolated when installed on the new model VP diesel engines. By installing additional isolation gaskets and some machining, our mechanic was able to mate it to and isolate it from the original MD22L engine.

To further protect the saildrive we discovered the VP Universal Active Protection kit. It is designed for VP outboard engines, but works like a charm on our Bavaria 38' Ocean 2000. Our Zincs n longer have to be replaced more than once every 18 months and even then they are still at 95%. And since the QL Acive Protection Kit only costs around US $200, it is cheap insurance for protecting an expensive Sail Drive which with installation will run you up to $ 14 K.


How it works:
The system uses an on board electronic control unit, with a reference anode and an active anode - both fitted below the waterline. The reference anode senses the electrical potential of the surrounding water and sends a signal to the control unit, which in turn sends an appropriate current to the active anode. Different combinations of water temperature, chemical composition and exposed surface require different levels of current. The active anode then emits varying levels of ions into the water surrounding the drive, and these ions effectively prevent galvanic corrosion, ultimately protecting the drive.

The QL Active Corrosion Protection System is designed for 12V electrical systems and has absolutely no moving parts, so minimum maintenance is required.

Features:

Helps to prevent galvanic corrosion.
Works with your aluminum or zinc anodes to protect your sterndrive or outboard.
Fits all sterndrives and outboards in saltwater applications.
Electronic control unit inside the boat has LEDs which let you know the drive is being protected.
Provides constant monitoring of the drive or outboard while in saltwater.
Low amp draw (3 mA) while in the monitoring mode.
Easy to install, no special tools required.
CE approved.
Not designed for use in freshwater or with magnesium anodes.
No moving parts.
Corrosion Protection System, Universal
The Active Corrosion Protection System helps prevent galvanic corrosion from attacking the metal parts of your sterndrive or outboard. This system complements the sterndrive/outboard sacrificial anodes and is not intended to replace those. The Active Corrosion Protection System is recommended for fiberglass boats that are used in saltwater with varying degrees of corrosiveness, or where extra protection against corrosion is needed. The system is designed to protect the mass of one sterndrive or outboard. An additional kit is required for installation on a twin engine boat.

[Kaptajnen]

Attached photo of the VP Active Protection Kit

[Kaptajnen]

Kit installed on hull - the "Reference Anode" shown here is installed on the port side and the "Active Anode" is on the starboard side. In between I installed a large zinc to further protect he saildrive.

[Salty]

Interesting picture Kaptajnen. Apart from whether the new fittings result in much loss of speed while underway, I'd be concerned by the staining on the hull which you can see leading aft from the sail drive penetration of the hull. Something is causing that stain, and if it was my boat I'd have that rubber fairing off to find the source, and get it rectified before it became serious.

[Kaptajnen]

Salty - the photo was taken 2 years ago - after the previous Saildrive had been destroyed by the stray current. So, the stain you noticed was caused by that catastrophic event.
Since then, there has been no re-occurrence of any stain, and the protection is working, both for my saildrive and aluminum prop (as well as the zincs).
As far as loss of speed due to the installed sensors etc. I have not noticed anything noteworhy.

[Kaptajnen]

And here is a photo taken when the boat was hauled out last August for a bottom paint job. The zincs, prop and saldrive look like new after a year and a half. The prop cone needed a new coat of protective paint and the sensors had some marine growth that we removed.

[Salty]

Ouch, that sounds like it was a real pain in the pocket!! But at least now with the VP Protection kit fitted that staining has gone, and hopefully the problems that caused it have gone with it. Did you have any warning of something going wrong before disaster struck, or were you lucky (in some respects) to get the boat ashore first?

[Kaptajnen]

Salty - No advance warning, but it all started when one of the two drive belts to the alternator broke and that in turn caused a major jolt to the alternator that destroyed one of the small isolation gaskets between the altenator bolts and the engine block. This was not noticed by the mechanic since the gaskets are hidden underneath the bolts.

So now the stage was set for the disaster; once we were hoked up to shore power, the stray current could flow from the saildrive to the engine block and via the alternator to ground. The next morning got a call from the marina that the boat was leaking oil (from the saildrive) and the Coast Guard were at the boat. We had a diver go down and confirm that the saildrive was leaking and on and on. No insurance cover for corrosion (electrical or otherwise) so at the end of the day a major hit on the pocketbook.

That is why I installed the VP QL Universal Automatic Corrosion Protection kit and that is why I am posting this thread on the Bavaria Blog so other owners of the VP saildrives might avoid this calamity.

It s really a "Belt and Suspenders" approach. The Saildrive must be isolated from the engine AND the engine must be isolated from electrical ground in order to protect the Saildrive from stray current.

[Nigel]

My entire engine is isolated from ground, except when stopping and starting.

[Salty]

Thanks for the heads up Kaptajnen, I think I'll add a periodic insulation check for my sail drive, but from your explanation even that might not be sufficient. Perhaps someone can think up an automated system that would warn owners in event of a breakdown of the insulation between the saildrive and any other metal parts.

[Nigel]

[This topic has been split, see here -  my reply left for info]

Does it not have a negative connection bolted to the engine block?...

Absolutely not. There is a negative connection next to the engine (MD22P-B), but isolated. The alternators and starter are also isolated (seperate ground connection, not through body). There is a relay that energises when starting and stopping, this momentarily grounds the engine via 55A fuse. Anyone who has this relay and fuse combination should make sure the engine is isolated.

See the file Volvo Penta 22 Series Instrument Panel & Engine Wiring Diagram DIY Manual on the Download page, relay and fuse are numbered 5 and 6.

[tckearney]

Hello Nigel  you seem to have a handle on this earthing business.  Can I ask a few basic questions?   Firstly when you refer to the engine being ?isolated? are you talking about isolated from the negative DC or from the shore side power earth.   Why do we need a shore power earth anyway.  It is only the UK that has Live Neutral  and earth (where earth is connected to neutral via the star point on the substation I believe) Europe USA and the rest of the world  is L1, L2 and earth and L1, L2 are not connected in any way the ground or earth and if you don?t need the earth then I assume there is no need for an iso transformer (assuming a none metallic boat that is)
Am I talking rubbish here? 
My anode on the sail drive does not seem to corrode in anyway whatsoever and I check it every year. This worries me somewhat.  Sail drive, keel and rudder all look fine.  Am I missing something or just think myself lucky that all is well.

[patprice]

I wonder how common it is to experience nasty problems with stray electricity and drive legs?
Is it common?
Anyone know?
Or just the very occasional very nasty occurance.

[Nigel]

...  Firstly when you refer to the engine being ?isolated? are you talking about isolated from the negative DC or from the shore side power earth...  It is only the UK that has Live Neutral  and earth ...

My MD22P-B  (as all the MD22 series I believe) has no battery negative connection to the engine block, it is isolated.

As far as mains earth is concerned, all countries have this in some form or another, as some electrical equipment needs it as a safety feature. Live and neutral are just the names we give the incoming feed in the UK, live being a higher potential from earth than the neutral. Don't be fooled, the latter can give you a nasty belt.

In my opinion there is no need to bond the incoming earth to any part of a GRP boat except the mains sockets, nor is it desirable.

[Symphony]

 
My anode on the sail drive does not seem to corrode in anyway whatsoever and I check it every year. This worries me somewhat.  Sail drive, keel and rudder all look fine.  Am I missing something or just think myself lucky that all is well.

That is not unusual. On my last boat which spent the first 10 years in Corfu in the med we changed the saildrive anode only once and then it did not really need it, but we were changing the seals and adding a rope cutter so made sense to put on a new anode rather than modifying the old one. The same boat now in the UK permanently in the water in a marina had some erosion and the anode was changed every 2 years.

There should be no erosion caused by galvanic action on the keel as it is cast iron and not connected to anything in water. However, if it is cast iron it may well suffer from rust unless it has been epoxy coated. There is some potential for corrosion of the rudder stock, particularly where it enters the hull and lower bearing which may be caused by copper based antifoul getting on it and in the aluminium lower bearing housing. However not every boat seems to suffer but it is worth keeping an eye on that area.

[Impavidus]

I think this web page will help explain the basics,   
Make sure you read the whole page. 
http://www.howequipmentworks.com/electrical_safety/

Ant.