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  #1  
Old 03-14-2008
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Sail drive

Here is a photograph of the sail drive on the boat I purchased in the fall. Is this pitting of the surface galvanic corrosion?
What do I need to do to repair this?

Thanks.
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Old 03-14-2008
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Oooh... that's not good... What kind of saildrive is it? There what kind of boat is it? The reason I ask what kind of saildrive and boat it is, is some boats and saildrives have known issues with corrosion.

Have you checked the electrical system on the boat to see that the electrical system isn't causing this? This can be caused by bad wiring on the boat or in your marina, or on another boat in your marina.

I'd ask you to post a larger photo, since that one doesn't really have enough detail, but you can't do that until you have 10 posts, and you'd need to have a flickr, picasa or photobucket account.

Might want to read this post to get the most out of your time on sailnet.
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Old 03-14-2008
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Notice the zinc is pristine while the casting is disolved. SD is right - bad wiring OR you have stray current in your marina. We had a stray current issue after a storm damaged the marina's shore power system.
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boat type

The boat is a Jeanneau Fantasia, 1984. The engine is an OMC Saildrive. I purchased it in the fall in the water. It did not get any use during the summer up until I bought it. I moved it to the current marina in the fall and then it was taken out of the water about three weeks later. It is in Lake Huron.
How would the wiring on the boat cause this - I mean what should I look for?
Thanks for your help.
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When you bought the boat, did the saildrive look normal?? If so, then it is probably a wiring problem in the marina, not in the boat. If the wiring in the marina is setup wrong...then you can get serious problems. From a Xantrex document on the issue:

Quote:
Grounding Inverter/Chargers on Boats

Preventing corrosion

For safety reasons, the two grounds should be tied together, but then the boat becomes vulnerable to galvanic corrosion. The reason for this is that when the boat is grounded through the shore cord, the boatís submerged metal parts become one element (or plate) of a battery (actually a voltaic cell). The water serves as an electrolyte, and any other grounded metal in the area (metal dock parts or submerged metal on other grounded boats), becomes the other element (or plate) of the battery. The AC ground wire effectively connects the two plates of this battery together, and a significant amount of DC (galvanic) current generated by this battery will flow in the AC ground wire. Depending on the type of submerged metal on the boat, and the types of grounded metals on surrounding boats, the boat in question could be the positive or negative plate of this battery. If it is the positive plate because its metal parts are more anodic or less noble than the surrounding grounded metal, then galvanic corrosion begins. To solve this problem, a galvanic isolator can be installed in the shorepower ground wire just after it enters the boat. This device will allow AC fault current to pass to keep the boat safe, but block DC galvanic currents to prevent corrosion. Isolation transformers will also perform the same function.

Grounding the inverter/charger chassis

What does this have to do with the installation of inverter/chargers? ABYC also recommends that the chassis of an inverter/charger be connected to DC ground. The chassis is already tied to AC ground via the AC

Grounding Inverter/Chargers on Boats

input and AC output green wires, so grounding the chassis to DC ground will create a bond between AC ground and DC ground that may not have existed on the boat before. If this is the case, galvanic corrosion begins and the inverter gets the blame for it.

The solution is to go ahead and ground the inverter/charger chassis to DC ground to meet ABYC recommendations, and also add a ground wire between the AC ground bus and DC ground, since this is where the primary bond between the two grounds should be established anyway. Then a galvanic isolator or isolation transformer is added at the shorepower inlet to prevent galvanic corrosion.
It could also be a wiring problem on a boat near yours in the marina. I'd contact the marina about this... one quick and easy test is to take a voltmeter, and attach the black lead to your battery ground pole. Then drop the positive lead over the side, into the water. If there is any significant voltage, it should show. Try the voltmeter in both AC and DC modes. BTW, stay out of the water until you solve this problem. It doesn't take much electrical current in water to kill you stone cold dead.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Last edited by sailingdog; 03-14-2008 at 04:55 PM.
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Old 03-14-2008
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A interesting blog that discusses issues of another owner with a saildrive...it demonstrates the worst of conditions (plenty of pics as well...)

Untitled Document
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Assumption is that you keep the boat in a slip w/ shore power, and do not have a galvanic isolator:
  1. Turn off *everything* on the boat. Plug in shore power cord to boat, but not the dock. Using a Ohm meter, check for resistance between the boat's grounding bus, and the ground on the shore power cord. Should be less than 0.1 Ohm
  2. Check for resistance between the grounding bus and the engine block. Should be less than 0.1 Ohm.
  3. Check for resistance between the grounding bus and the SailDrive unit. Should be less than 0.1 Ohm.
  4. Check for resistance between the grounding bus and the zinc pictured above. Should be less than 0.1 Ohm.

If it passes all of these tests, the problem is in the marina, and not on your boat.

To fix the existing damage assuming that it is pitting caused by galvanic corrosion; sand the metal until the damage has been removed, and/or clean with phosphoric acid and a stiff bristle brush, and adequate protection (rubber gloves, glasses, etc.)

Good luck!

Ed
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There is a registered marine electrician at the marina and I will have him look at the boat wiring. I was planing on having the AC checked anyway.
Can this corrosion be repaired? What do you suggest that I do?

I did not see the state of the drive when I purchased the boat as it was already in the water. Could this have been done in three weeks at the marina where it is currently stored?

Thanks,
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Peter-

The higher the voltage leak, the faster the damage. I know of one aluminum sailboat that had to be total lossed after staying in a marina that had an electrical problem after two weeks. The hull had been eaten away to the point it wasn't considered repairable—less than 1 mm thick in some places IIRC.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 03-14-2008
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From your picture and further descriptions it is not at all clear to me that you have galvanic corrosion. Give the reputation of OMC's it is LIKELY but not certain especially since you are in fresh water.
I would soda blast the lower unit down to clean metal to ascertain if it is still serviceable and to determine the extent (if any) of galvanic corrosion present.
I would prep and paint the lower unit if no damage is found while also using your electrician to insure stray current is not an issue.
If significant damage is present, you are looking at a big bill since OMC is not repairable at this point in time on a major rebuild.
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