Anodes+Galvanic isolator queery?

[RobWales]

Hi All,(happy new yr)....

On discovering my boat does not have a galvanic isolator fitted I have on order a 70amp unit from a manufacturer who sells on ebay.

My previous boat,Bayliner with B3 drive used to go through 2 sets of anodes per season and that had the mercathode system fitted.

Current boat has VP 290 Dp's with stainless props and my marina berth see's me quite close to one of the steel pylons.

Have I done the right thing in ordering this unit and will it help the life of my anodes (brand new last week).

Shorepower is running 24/7 to keep the dehumidifier going.

Thanks
Rob

 

[dkm]

with SS props its unlikley you will get a full year out of your ring anodes, particularly if you follow manufacturers instructions and change when they are 50% eroded. You may get some protection with remaining anodes which may stretch them to a 12 month change as opposed to 6 months but depends on the specifics of your berthing environment. Think of your galvanic isolator as an insurance policy rather than something that will automatically and significantly reduce erosion of prop anodes

 

[Elessar]

Hi Rob,

My sealine didn't have a galvanic isolator and the anodes were gone in a couple of weeks when I moved to Shamrock Quay. 2 props ruined beyond repair too. The isolator is essential. Wear returned to normal when it was fitted.

The Mercathode slows the erosion of anodes in normal conditions. It cannot cope with a fault condition in other boats/the pontoon which is what the galvanic isolator guards against. Fit urgently and until you do unplug your shorepower.

The Balyliner would have had one, they fit as standard, but the stainless props on a B3 accelerate anode wear.

ps the person you put me in touch with is testing Evenstar next week so hopefully I'll have a sale and I'll owe you lots of beer!

 

[RobWales]

Thats very good news indeed so 2009 may turn out to be the start of a good one for you!
I have no doubt he will be impressed as he seems to know what he wants and lets be honest they are superb with that motor drive combo.
Good luck and keep us posted.
Rob

 

[VicS]

Yes if you have shore power plugged in, even if it is not in use, you need a galvanic isolator to prevent excessive wastage of the anodes (assuming the shorepower earth is connected to the anodes) otherwise they are "fizzing away" protecting all the steel piling in the marina and that big steel boat in the next berth!

 

[RobWales]

Back in 5 mins chaps................
Off to marina to unplug the shorepower!

 

[mightymouse]

New to boat repair and maintenance here in Hastings.
I take it there is some sort of electrolytic reaction that goes on with current leaching from the boats electrical system, through the out drive and the water to ground?
And there are anodisors which reduce this?
Are they expensive? Large? /required for a small runabout like mine?
thanks all
Mightymouse
http://www.tribidium.com/matt/boatpics.html

 

[VicS]

[ QUOTE ]
I take it there is some sort of electrolytic reaction that goes on with current leaching from the boats electrical system

[/ QUOTE ] There may be and it may be due to obscure faults on nearby boats but I've never seen a satisfactory explanation.

Whether or not that is a problem the trouble is probably that a nearby steel hull also on shorepower or steel piling driven into the ground are all connected to your anodes via the earth wire in your shorepower lead. Your anodes can therefore be trying to protect all that lot.

The galvanic isolator is a device that will block the flow of current from very low voltage sources such as these galvanic ones, but will still allow the current from high voltage sources like the mains electricity supply to pass and so give you and your system the protection that is normally given by earthing. Because the effects of defective low voltage installations are driven by 12 (or 24) volts it is doubtful if a GI will offer protection from the effects of that sort of thing

If you have sacrificial anodes and leave a shorepower supply connected, not necessarily in use, then they are pretty close to being essential. As always though "dont fix what ain't broke"

It must be rated in excess of your mains fuse or circuit breaker.

 

[Elessar]

You MUST have anodes to protect anything that is metal and not marine grade stainless steel that touches the water. This includes the insides of the cooling system of your engine.
More details of the boat and where you keep here would be necessary if you want people to give you more pointers.

 

[John100156]

I wonder if a simple contactor and timer circuit could be used to reduce wear?

A 12vdc contactor and timer driven from the battery (very low current so minimal drain). When energised, it disconnects the shore power for say 12 hours. It then de-energises and restores shore power for 12 hours? Surely this would reduce wear by 50% and is fail safe, if the contactor drops out or battery voltage drops, the shore power is restored and charges the batteries again?

What do you think?

 

[VicS]

[ QUOTE ]
What do you think

[/ QUOTE ] Unnecessarily complicated. 12volt timers may not be as easy to source as you think. its only going to be reducing the trouble by the amount off time the shorepower is off. You have to disconnect the earth not just the live and neutral.

Galvanic isolator is the simple and effective solution IMHO.

 

[Skyva_2]

Hi,

do you keep your boat in the water?

The right anodes are essential but galvanic isolator is not necessary unless you have shore power connected.

 

[VicS]

[ QUOTE ]
You MUST have anodes to protect anything that is metal and not marine grade stainless

[/ QUOTE ] Bronze props and bronze or DZR skin fittings should not need cathodic protection.
Bronze brass etc fittinsgs should not be connected to the same anodes as ferrous items.

The engine cooling system is a special case and inspection/ replacement of the internal anodes (where they are fitted) should be part of the routine engine maintenance just as oil changes are.

 

[RobWales]

[ QUOTE ]
Back in 5 mins chaps................
Off to marina to unplug the shorepower!

[/ QUOTE ]

Switched off and unplugged until I'm able to install my new GI.
Thanks all.
Rob

 

[Elessar]

RE bronze and DZR - I didn't know that and I'm sure mine are connected - ie skin fittings and engine.........

 

[Pete7]

[ QUOTE ]
Back in 5 mins chaps................
Off to marina to unplug the shorepower!

[/ QUOTE ]

/forums/images/graemlins/laugh.gif

Did the same yesterday, replaced the earth lead to the annode and connected the nearby raw water strainer in as well. Rowed ashore, changed my mind and went back to disconnect the strainer. Looking at Vics post this morning glad I did.

Pete

 

[John100156]

Most timer chips are low voltage and a simple 12v timer circuit can be built very easily. Yes you would need to have a standard three contact contactor: L/N/E - the E has minimal current so the contacts would never wear.

Thats the point - by having 12h on/off you reduce by half the possibility of galvanic activity - 2 seasons instead of one!

But instead of a timer, how about a simple photocell to energise the contactor at night!

I have a GI but this still permits a small by-pass. You could fit both!

 

[RobWales]

I like your thinking John................
If your gonna build a unit then I'll have one too please /forums/images/graemlins/grin.gif

 

[VicS]

[ QUOTE ]
RE bronze and DZR

[/ QUOTE ] One of the recommendations by the MAIB investigation into the near loss of the fv Random Harvest (q.v.) off Brighton some years ago was that the skin fittings should not connected to the anodes. (Main reasons for their troubles was that "Tonval" fittings had been used and not inspected)
Bronze or DZR brass are resistant to seawater corrosion and should in ordinary circumstances not need cathodic protection (Similarly manganese bronze props which everyone sticks shaft anodes on to protect)

 

[John100156]

Quick google shows lots of 12vdc timers but probably over engineering:

How about a simple 240v contactor/timeclock in a waterproof box installed when leaving the boat in the shore line that when energised completely isolates (effectively unpluging) the boat say every 12hrs for as long as you like! About 1/6th the cost of an isolating transformer, which I suppose must be the best solution? /forums/images/graemlins/confused.gif

I only run my charger and rarely a dehumidifier when not on the boat, would rest the charger prolonging its life, reduce galvanic action by say 50%, with no detrimental additional drain on the batteries.

So why dont we do it, whats the problem with this?