Swim Platform Support Strut Electrolysis

OlygirlNav

Well-known member
Joined
Sep 24, 2017
Messages
50
Fluid Motion Model
C-30 S
Vessel Name
Cool Mint2
Our boat is kept in the water year round since July 2017. In the haul out this year we found two screw heads that fell off when touched on the swim platform. Looks like electrolysis. Solution is to put a zinc on each of the swim platform support struts. I posted a picture on the Cool Mint album so you can see the screw heads missing. In the boat yard I did observe most of the boats had zincs on their swim platform supports.
We are also going to have a wire from the zinc on the trim tabs to the stern of the boat trim tab screw to help prevent electrolysis on the trim tab hinge.
No stern zinc as we have outboards and the zinc installer did not see a reason for the zinc.
 
I have zincs on my swim platform struts, they last a long time compared to the other zincs on the boat.
 
Interesting. Each of our struts are tied to the boat bonding system inside the boat. Never had a problem.

Thanks fo the idea for protecting the trim tab hinge. I often wondered if the questionable electrical contact through the hinge could be an issue. Haven’t had a problem yet but it is something I will watch for.

Curt
 
A couple of ideas that come to mind.
1) Are your platform supports properly Bonded? If so is there continuity from the support to the grounding bus? If not this may be a problem.
2) When your zink installer repairs the support fasteners, suggest using 316 ss fasteners instead of 304 ss. and confirm sound contact and bonding.
3) Ask your zinc installer about using Aluminum alloy anodes instead of zinc. The aluminum alloy has proven to give better protection and last as long and in many cases longer then Zinc anodes. The aluminum alloy anodes are recommended by most outboard manufactures and Thruster manufactures to better protect their product.
4) Galvanic Isolator if not installed would be a good addition to adding electrolysis and galvanic corrosion protection. The isolator has its limitations if the dock or harbor has a lot of activity but it will help.
5) wire bonding the trim plane to the hinge plate is a good idea. This is done on all outboards and stern drives. Every mating surface is connected by a bonding plate or stainless steel cable so anode protection is protecting the components as one unit.
6) installing anodes on the swim platform support is also a good idea. The issue with this install is confirming continuity from the surface of the anode to the support, no continuity it doesn't work. The anode if Zinc must be low enough that it doesn't continually have oxygen. The zinc will form oxidized coating on it and will become inactive. Similar to using zinc on trailerable boats or in fresh or brackish water they become inactive from this coating. Aluminum anodes do not do this.
Mercruiser, mercury marine, Volvo, and Outboard Marine Manufacture quit using Zinc in the late 80's early 90's and started using the aluminum alloy anode because of corrosion issues because of less protection from Zinc anodes.
 
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