Painting strut/shaft

[azazzera]

I think I read somewhere that the strut and shaft should not get painted. I see many boats in the yard that have there strut and shaft painted. Most likely I read it on this forum, that a bare clean shaft and strut is needed for proper zinc working and also to ground the engine properly. Do I have this correct. Thanks.

[GregH]

Interesting.

I have never heard that (doesn't mean there's not something to it). I don't have a strut on my boat but I cannot see how it would be needed for grounding as the cutlass bearing would be in the strut and the rubber in that would separate the engine electrically from the boat.

[Administrator]

Here's my approach:

Remove the old zincs.
Sand the shaft shiny. Clean up the strut and prop.
Apply the zincs to shiny metal.
Tap the zincs with a hammer and retighten.
Tape the zincs.
Paint the shaft, strut and prop.
Remove the tape from the zincs.

Bill

[Mo]

Here's my approach:

Remove the old zincs.
Sand the shaft shiny. Clean up the strut and prop.
Apply the zincs to shiny metal.
Tap the zincs with a hammer and retighten.
Tape the zincs.
Paint the shaft, strut and prop.
Remove the tape from the zincs.

Bill

Roger that, or any reasonable facsimile there of. I use ablative paint so I don't sand it all down...just add more. New zincs anode yearly and there is a place bare of paint when you take the old one off. I do the bottom painting first then remove old anodes...new ones go on the bare spot.

[edwardc]

How timely. I'm wrestling with this very problem now.

I have always read that copper-based bottom paint should NEVER be applied directly to underwater bronze. I always use a zinc paint for the prop and shaft.

As for the strut, a previous owner seems to have sealed it up in a combination of fiberglass and some sort of fairing compound, and then painted it with copper paint.

The problem is that the coating has lost adhesion with the cutless portion of the strut and is flaking off. Removing it all has revealed that it has been letting water in for a long time, and there is significant pitting.

My current plan, subject to more research, is to grind the strut down to bare metal, and then coat with Pettit Zinc Barnacle Barrier, which I've used with good results on the prop.

[JOHN COOKSON]

The problem is that the coating has lost adhesion with the cutless portion of the strut and is flaking off. Removing it all has revealed that it has been letting water in for a long time, and there is significant pitting.
My current plan, subject to more research, is to grind the strut down to bare metal, and then coat with Pettit Zinc Barnacle Barrier, which I've used with good results on the prop.

To be safe I'd put a "clam shell" zinc on the strut also. I did this many years ago at the suggestion of my diver. It took care of any and all electrolysis problems on the strut.

TRUE GRIT

[azazzera]

I was mainly trying to refer to bonding and cathodic protection. My reference is from N. Calder fourth edition page 279... I have my chainplates connected to a bolt on the strut and a wire run to the neg. bus. I have no AC onboard. I did not ret run a jumper across my coupling as described or set up a spring loaded brush system. my understanding is that this is useful in providing high voltage path to ground for lightning strikes, and "Prevent damage to underwater hardware from stray currents originating within the boat by providing these currents with a direct path to battery negative that precludes their passing through any underwater hardware". So my question is if shaft and or strut gets covered with paint whatever the type it no longer can connect with earth c
ground.

[ndutton]

Not clear on what you're protecting with the strut and measures are different for different purposes:

• If you're using the strut and driveline as a lightning ground you'd better have as much bare metal in contact with the water as possible although I'm not too sure of the wisdom considering a million volt strike will likely blow holes in the hull where the driveline penetrates. If that happens the lightning strike will be the least of your worries.
• If you're trying to protect the strut casting from galvanic corrosion, a specific zinc bolted through the strut web achieves that http://www.boatzincs.com/rudder-size...iABEgKf_fD_BwE
• Stray current corrosion is not a concern because no shore power connection.
• Anything I'm missing?

[sdemore]

Side question Neil. What is the proper way to ground the mast? I have a big cable coming off the mast, which I assume is a lightning dissipation path, but no idea of where it should be connected. I have a bonding point on one of my strut bolts that I was going to connect it to, but if that isn't a good place, is there a better one?

[ndutton]

I'm probably the last person who should be offering advice in lightning protection because I've never lived or boated in a lightning prone area so take the following for what it's worth - - - which is exactly what you paid for it ($0.00)

Rather than risk destruction of vital underwater gear, installation of a grounding plate to the exterior of the hull is popular. Products such as a Dynaplate are made of sintered or porous bronze to provide a much greater equivalent surface area in contact with the water than it's physical size. The grounding cable, usually somewhere around #4, connects from the mast base* to the grounding plate mounting bolt. Location should be as directly below the mast as possible to keep the run short and direct.

Some skippers connect the chainplates to this system to include the standing rigging but at the factories this was frowned upon because of potential damage to the turnbuckles. The thinking at the time was if a skipper preferred it, connect only one (usually an upper shroud). In the event of a strike he'd weld only one turnbuckle instead of all of them.

I don't know if the foregoing is accepted protocol these days. Back when I worked at the boat factories it was a contentious issue. Ask 3 sailors, you'd get 4 opinions.

*assumes aluminum mast