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  corrosion on new suzuki install, galvanic? Please help!

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Author Topic:   corrosion on new suzuki install, galvanic? Please help!
detra posted 08-05-2003 09:10 PM ET (US)   Profile for detra  
I've got a nauset with a suzuki df70 on a cmc aluminum jack/setback plate. Brought the engine in for its 20 hour service and discovered some corrosion on the aluminum prop. Also the dealer said the zinc was almost used up. The boat has been used exclusively in salt water, always trailered and flushed/rinsed after each use per manufacturers instructions. Is this "typical" galvanic corrosion or do I have a voltage leak somewhere.

The wiring is "original" style with only a bow/stern push pull switch, tack and trim gauges, and compass. I currently have the lights and compass "grounded" back to the negative battery post. Is this correct, or should there be some alternative grounding system used.

Next season I plan to rewire with a fusebox and voltage regulator as per triblet post. Meanwhile, I will disconnect battery when not in use. Thanks for you input.

Jamie 20 outrage posted 08-05-2003 09:33 PM ET (US)     Profile for Jamie 20 outrage  Send Email to Jamie 20 outrage     
Unfortunately, disconnecting the battery when not in use may not help much. This problem can do alot of damage when connected and being used. It doesn't sound normal at all. You need to buy an electolysis kit. ProMariner I believe sells one at West Marine. The idea is to set it up and see the bad numbers and start disconnecting electrical items, either by removing a positive wire or removing fuses one at a time until you see a change in the meter. If the solution is not obvious, at least you will be able to give your dealer enough info to help diagnose it. Be aware that bilge pump or float switch[if you have one] can be at fault. Another thing to do is to run things like your trim and tilt and see if the meter changes, run the engine and look, your lights, etc. I hope this helps.
detra posted 08-06-2003 08:57 AM ET (US)     Profile for detra    
Thanks for the information. I plan to rewire everything non-motor as well as check all the motor/control wiring that the dealer installed. The dealer did not inspire confidence. I sill have a question concerning a proper ground. Is it OK to have the negative post on the battery serve as the ground or is there some other possibility. This is a 1973 whaler with original wiring scheme, with newer wires and a couple of distribution buses.

I think stray current is the problem, possibly from wires passing through the tunnel. What is the best way to waterproof tunnel wires?


HAPPYJIM posted 08-06-2003 01:00 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Don't use splices in the tunnel.
Boat wiring is waterproof as long as the insulation is not nicked or cut. Splices have to be MADE waterproof.
lhg posted 08-06-2003 01:43 PM ET (US)     Profile for lhg    
The aluminum jackplate (with SS connecting bolts) will generate a lot of galvanic activity. Mine sure do, so I have installed Mercury's excellent aluminum based (NOT ZINC based) bolt anodes on any 1/2" course thread bolt threads that are under water. I can tell by the rapid degradation in these anodes that they are doing a lot of work.

On each bracket I have installed four of these, including two on the lower engine-to-bracket mounting bolts. These should be installed with the threads and nut out, and the bolt should be long enough so that the threads are exposed about 1/4" beyond the nylock nut to receive the screw-on anode. Highly recommended that you do this.

Mercury's patented aluminum anodes, used on all Merc outboards and I/O's, give much better protection than zinc.
The bolt anodes are actually an I/O product. They are only available packaged by Mercury. All the non-OEM stuff is zinc only.

Also, be sure to use anti-seize compound on the large threaded lifting shaft where it contacts the aluminum bracket components.

detra posted 08-06-2003 04:54 PM ET (US)     Profile for detra    
Thanks for all the info. My tunnel wiring is new last year, no splices. There are no jury rigged connections anywhere on the boat, and all wiring is marine grade new.

Thanks lng for the info on galvanic protection on the jackplate. I used "zinc' generically as it is the stock protection on the suzuki. I will replace with merc ASAP.

One other possibility was that the tilt meter when installed was nonfunctional, maybe it was leaking current? The unit was replaced at 20 hours service and now works. I am thinking that the sender could have been bad and may have been leaking current.

Hopefully these changes will solve my problem.

jimh posted 08-08-2003 11:10 PM ET (US)     Profile for jimh  Send Email to jimh     
My engine is mounted with the 1/2-18 (UNC Fine) SS bolts. They don't thread very well with the 1/2-13 (UNC Coarse) threads on the Mercury aluminum anodes.

I wonder if I could re-tap them? It might be worth a try.

triblet posted 08-09-2003 09:51 PM ET (US)     Profile for triblet  Send Email to triblet     
The bolts you have are UNF (Unified National Fine), not "UNC
Fine", and the anodes would be UNC (Unified National Coarse),
not "UNC Coarse".

I doubt you could retap from UNC to UNF (or vice versa).

Aluminum is also a little bit tricky to tap. Do a little
research on lubricants, and go slow, and back the tap up
frequently to break the chips.


lhg posted 08-11-2003 03:56 PM ET (US)     Profile for lhg    
I made sure I mounted the engines to the brackets with course thread bolts. However, the brackets are mounted the thick Whaler transom with the Mercury supplied fine threaded bolts, and brass nylock nuts.

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