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Old 09-05-2015, 14:08   #1
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Inspecting stainless rudder post

Hi everyone,

Since its roughly her 50th birthday, I figured I'd thoroughly inspect the rudder post, particularly where it passes through the hull + stuffing box, etc and you can't generally see it.

Already after removing some superficial flashing around the top of the rudder assembly, I have revealed some pitting thats probably a mm or two deep, pock marks like that are all over one section. (see photo, attached). I'm wondering how to interpret this.

Maybe by describing the whole assembly I can get opinions on if it sounds like overkill with a good deal of safety envelope, or not...

The rudder post is solid, not hollow, and about 1 5/8" (40mm) diameter.

The boats a 11-12 ton yawl, 41', with probably 6-8 square feet of rudder hung along the aft edge of the cutaway/full keel.

An interesting thing with this assembly is that the post is separate from the rudder. The bottom end of the rudder post, which ends up just under the hull when installed, is splined. There is a mating splined hole in the hefty bronze casting that makes up the frame of the rudder (this casting, plus drift pins, plus wood makes up the rudder). The rudder is also supported by a pintle/gudgeon assembly doodad just below the propeller aperture as well as a pin that rests in a shoe extending along the foot of the keel.

For this reason its sort of easy to remove the whole rudder post from the rudder, so having a new rudder post made is an option.. but an expensive one..

Thanks for any opinions!

EDIT - (for anyone paying particularly close attention to that photo, its showing up upside down for some reason here)
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Old 09-05-2015, 23:30   #2
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Re: Inspecting stainless rudder post

Update, it looks like that one patch is the only spot with corrosion. The shaft inside the stuffing box was fine, oddly enough. Still contemplating replacement, but removing it outright (as opposed to just sliding it up enough to view the normally hidden bits) is a lot more involved. Turns out its a standard tapered, keyed fit and not a spline, so machining a new one ought to be straightforward at least.
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Old 13-05-2015, 00:19   #3
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Re: Inspecting stainless rudder post

Salt water causes some alloys of stainless to corrode in the absence of air. I don't think those pits are enough to worry about. If that part of the post doesn't pass thru some bearing or seal, you could weld the deeper pits. If it can be turned on a lathe, it could be welded oversize and turned down. Any good machine shop should be able to do it. Was it protected by a zinc?
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Old 13-05-2015, 14:35   #4
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Re: Inspecting stainless rudder post

I agree I would not be very concerned. If that is 50 years I would go a few more dozen. These days there are so many good anti-corrosion substances you can use that depending on the friction at that point, you have many choices. It doesn't look like it is getting any rubbing there. Lanacote, ACF 50 or something. If you have any sort of drip or remote access to that part of the shaft you can also just drip some anti-corrosion down there once in a while.

I want to pull my rudder on Aeolus some day and haven't yet. Just hoping it doesn't snap off in a steep 8' SE 40 knot Strait of Georgia sea this summer or next!
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Old 13-05-2015, 15:19   #5
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Re: Inspecting stainless rudder post

As you will be removing all the wood anyway, how about a patch sleeve welded over it.
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Old 14-05-2015, 13:35   #6
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Re: Inspecting stainless rudder post

Thanks for the responses everyone.

I wimped out though and just sent off a diagram to a machine shop.

In answer to Lepke's question, the only zinc protection it has is via the bonding inside the boat that attaches this (from a wire on the quadrant) along with all the seacocks to a giant zinc plate.

When I assemble the thing, and reattach some bronze flashing that wraps over the rudder post and helps fair up the whole rudder + post assembly, I'll be tempted to scuff the stainless before applying bedding compound to take up the space under the flashing. Not sure this is the right thing to do though, since I'll be scuffing off the passivation layer.
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