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Old 10-15-2017, 03:17 PM   #1
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rudder question

I've got a couple rudder questions. I think the rudders on my Marine Trader may be stainless steel, since they show no sign of rusting since the boat was soda blasted a few weeks back. My questions are:
  1. Should I coat the rudders and struts with the same bottom paint that goes on the hull?
  2. I see there are two holes in each rudder. Should I install two sets of zincs? If not, what do you suppose the purpose is for that second hole?
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Old 10-15-2017, 04:21 PM   #2
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As to question 1, if they are SS rudders, or perhaps even if they are not but any metal, I would consider using a product such as this first, followed by your usual anti fouling paint: Pettit Underwater Priming Kit.

I used it on our SS prop cage with good results. First year we had the cages I did not use this product and the anti fouling did not adhere. Now it does.

As to question 2, can't opine on why two holes but I'd just put single hole clamshell zincs on them.
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Old 10-15-2017, 04:29 PM   #3
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Use a magnet to determine stainless or not - magnet will not be attracted to stainless of acceptable quality. Perhaps 2 holes indicated a zinc with 2 bolts, like a trim tab zinc, or 2 separate zincs were attached.
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Old 10-15-2017, 06:43 PM   #4
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Mine are stainless. I coat them the same as the bottom. Only one zinc per rudder. I'm guessing yours either had 2 zincs or one larger zinc that required 2 fasteners.

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Old 10-15-2017, 07:00 PM   #5
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#1 Bottom paint the rudders using the appropriate primer. As suggested a magnet will tell you if ss.

#2 as suggested either used two small zincs or one larger one that needed two holes
Or as I do use a flat plate piece of zinc and drill two matching holes.
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Old 10-15-2017, 08:11 PM   #6
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Quote:
Originally Posted by Chrisjs View Post
Use a magnet to determine stainless or not - magnet will not be attracted to stainless of acceptable quality. Perhaps 2 holes indicated a zinc with 2 bolts, like a trim tab zinc, or 2 separate zincs were attached.
But remember 300 grade stainless will still pull a magnet to it, it wont stick but you can feel the pull, so regardless if it's Stainless or not coat it.

Those 2 holes are for anodes, switching to a 1 bolt anode may not be enough anode for the intended attraction. If there are 1 bolt anodes with enough thickness and area as 2 bolted it doesn't matter if it's 1 or 2 bolted.
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Old 10-15-2017, 11:28 PM   #7
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On sailboats the hole is used to run a rope though with a knot on both sides and led back up on deck. This is done when you lose your steering system and allows you to steer by pulling on the appropriate end of the rope.

Never heard of it being done on a power boat.

If there is only one hole, usually that is where a zinc is attached.
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Old 10-15-2017, 11:50 PM   #8
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The rudders may be gun metal. It's grey in color and a type of red bronze. About 88% copper, 8-10% tin and 2% zinc. Sometimes the zinc is replaced with lead.
It was originally used to make cannons, but now is used for valves, pump parts and steam fittings.
If the rudders look cast rather than welded, they probably are gunmetal.
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Old 10-15-2017, 11:54 PM   #9
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A file will tell if SS or bronze.
Yes bottom paint.
What zincs were on there when boat pulled? Do you have any pictures from before? They might show.
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Old 10-17-2017, 09:33 PM   #10
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You can see they're welded so almost certainly SS. Either way, clean them up, prime them with something good like an epoxy, and antifoul them. Just like the props, struts, and shafts (& everything else metal under there). The antifoul question is one for the ages; don't use anything soft is all I'm sure of. Propspeed is horribly expensive but I've heard good things. I'm thinking of trying propFX next time on mine, as it's only mildly expensive compared to normal antifouling.

I'm going with the teardrop zinc theory about the holes. You're probably fine just using one rudder zinc in either hole, though, if you can't find an elongated one.
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