Bonding Failure Prop Zinc

K

Kaptajnen

Well-known member
Joined
Jan 28, 2018
Messages
258
Fluid Motion Model
C-302 C
Vessel Name
Akvavit
Our prop zinc used to last 4 months and still have plenty of zinc left.

Yesterday, our diver discovered that the zinc was completely gone after 4 months and he recommends to replace it after only 3 months.

I am wondering if the bonding to the drive shaft has failed. How do I check if that is the case? Could it be anything else?

Thank you.
 
There is no special bonding to the drive shaft that I know of unless you or a prior owner have added a shaft brush. Normally the bonding is achieved (arguably not so well) via the transmission. Even if there were a bonding issue then you would likely have less consumption of your prop zinc and not more.

If you do not have a galvanic isolator and you are plugged in at a marina the difference is likely the other boats at the marina. If they are not properly zinc’d you could be providing protection for them via your prop zinc. You could also have something else in or on your boat that is submerged and bonded creating the added current.

In any case it is not a bad idea to at least check your prop zinc every three months. I often at least have to tighten mine. Six months of life is really good for me. Never get more than that.

Curt
 
Curt,

Thank you!

I do have a galvanic isolator, and i will add a shaft brush at my next haulout.
 
You don't need to haul the boat out to install a shaft brush. It can be done while boat is in the water. Just make sure the shaft brush is installed correctly and without to much drag/friction on the shaft and it attached to the existing bonding of the boat such as the rudder bolts which should have large diameter green wires attached.

If you keep boat at marina in the water then suggest you disconnect your boat from the shore power pedestal (N.B. remove the connector and not just flipping breaker to OFF) for at least a week at a time and only reconnect it for 24 hrs at a time. This is what I do now and my prop zinc goes for at least 9 months where it typically is just below 50% after these months.

As an aside, I installed a GFI because my underwater zincs were needing to be replaced every 3 months (on a 2010 R25 Classic) with the exception of the trim tab zincs. The GFI did absolutely no good for me. Connecting to shore power for 24 hrs each week was the most effective thing.
 
Although I have a galvanic isolator I also use a sacrificial zinc that I drop in the water while at a slip. They say you can have too much zinc protection, but this has worked well for me.
 
Kaptajnen":3cpm0b0r said:
Our prop zinc used to last 4 months and still have plenty of zinc left.

Yesterday, our diver discovered that the zinc was completely gone after 4 months and he recommends to replace it after only 3 months.

I am wondering if the bonding to the drive shaft has failed. How do I check if that is the case? Could it be anything else?

Thank you.
Click to expand...

One other thought. When you say the zinc was completely gone do you mean it was missing? If so, that is a different issue. It is a common problem to have those prop zincs spin off. As the zinc is consumed it gets shorter and the zinc becomes loose. The bolt then either backs out or the zinc just breaks up due to the rattling forces. If your zinc is completely missing along with the bolt be sure to use plenty of thread locker on the bolt holding the new zinc. Apply the thread locker well in advance to use and let it dry completely if installing the zinc while in the water. Even if the bolt did not back out there are several other tricks to make the zinc more secure and not break up. You can apply a little paint (nail polish works well) to the mating surfaces on each end of the zinc. Just make sure there is still electrical contact with the prop nut. To make sure there is contact and to provide an additional tight fit wedge a small stainless washer between the prop nut and the zinc (i.e, place the washer on flat of the nut before installing the zinc).

Curt
 
Placing washers to avoid the prop zinc from falling away is a technique my diver service has employed for me since 2009. I will try and draw a schematic to show how this is done and post back here later.
 
Found the Promariner Shaft Brush at Hodges Marine for $21.
With free shipping and no tax.
 
Thank for the photos.

I have one more question.

I will need a 6 foot long bonding wire, minimum 8 AWG (according to the ABYC) with Ring Lugss attached (see photo in my album)

I need this to connect from the Promariner Shaft Brush to the nearest ground.

where can I find this item ready-made?
 
The Electric Motor Company fabricates #6 AWG Bonding Harnesses with Ring Terminals and Green vinyl jackets to order,
so that answers my above question.
 
West Marine will also custom make cables for you.

Curt
 
I installed the Promarine Shaft Brush on our boat today. There is a photo in my album that shows the Installation.

There was nothing easy or trivial about the installation. It involved working as a contortionist in extremely confined space, especially when attaching the bonding wire to the tiny screw that holds 3 other bonding wires.

Anyway, it is done and I hope that my prop zinc will last longer...
 
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