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Author Topic:   Aluminum set back bracket corrosion
Slippery Eel posted 09-26-2006 09:39 AM ET (US)   Profile for Slippery Eel   Send Email to Slippery Eel  
I have a CMC 4” set back bracket on my 79 montauk with a 2006 90 E-Tec hanging on it. When I leave it in the slip for a week on vacation I am getting a lot of growth or electrolysis on the bracket bolts. It does not appear to be algae. The growth is concentrated specifically on the stainless steel adjusting bolts on the bracket. I have installed a zinc on the hull mounted to a piece of starboard that is attached to the hull with 5200. There does not seem to be any deterioration to the zinc although it is under water while at the dock. Do I need to connect the zinc to the aluminum bracket to form a bond between the 2 to stop this? I am afraid that the bolts will ultimately seize and I am trying to prevent this.

Any thoughts are appreciated.


Chuck Tribolet posted 09-26-2006 10:25 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Zinc on starboard does you NO good. It has to be well and
truely electrically connected to what it's protecting.

I'll bet the stuff you are seeing is white? That's the
AL sacrificing itself to protect the SS. A zinc bolted to
the bracket should solve the problem. Zincs come in lots
of form factors, including some that are like washers.

You might ask CMC what they recommend -- they've been around
long enough to have run into this before.

Is there any shorepower run to the boat when in the slip?


Slippery Eel posted 09-28-2006 06:39 AM ET (US)     Profile for Slippery Eel  Send Email to Slippery Eel     

Thanks for the feedback. I will relocate the zinc to the bracket and ditch the starboard install. The stuff on the bolts is kind of off white and is pretty uniform in its growth pattern. I will check with CMC as well.


davej14 posted 09-28-2006 09:43 AM ET (US)     Profile for davej14  Send Email to davej14     
Make sure the zinc is in the water after you re-attach it to the setback bracket or it will not do you any good. The zinc needs to be in the water with a good electrical bond to the bracket.
ratherwhalering posted 10-01-2006 11:03 PM ET (US)     Profile for ratherwhalering  Send Email to ratherwhalering     
Hutch, I have the exact same set-up, and added some Delron washers underneath the SS washers. $2.00 a pop at TAP plastics. Works well, but sounds like you still need the zinc.
jimh posted 10-02-2006 09:52 PM ET (US)     Profile for jimh  Send Email to jimh     
It is a good idea to periodically check the resistance between any sacrificial anode (such as a zinc or magnesium electrode) and the battery negative terminal of the vessel's electrical system. There should be zero-ohms of resistance (or very low resistance) between these anodes and the battery negative. If the anodes are not bonded to the battery negative they do not provide much protection.

Check that all of the chassis components of the motor, such as the mounting bracket, the mid-section, and the gear case are also well-bonded to the battery negative. Generally there are small flexible conductors which make good electrical connection between all of these movable components to keep them bonded (electrically).

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