Crevice Corrosion - Is My Rudder Toast ?

[senormechanico]

Originally Posted by barnakiel

THX for explaining the matters. I will use a thickwalled pipe then next time our windvane shaft breaks (oh yes, it will).

I remember Najad started using aluminum for stock some time ago, I have also seen carbon rudder stock somewhere on the web.

Reading your post I thought if Titanium would do(?) Maybe a titanium pipe , thick-wall (if such a thing exists) would be both light and strong?

b.

If your windvane is a Monitor, the paddle shaft is designed to break when it hits something to prevent damage to the rest of the unit.
That's one of the reasons to have a line tied through the hole at the bottom of the paddle.

[barnakiel]

Originally Posted by senormechanico

If your windvane is a Monitor, the paddle shaft is designed to break when it hits something to prevent damage to the rest of the unit.
That's one of the reasons to have a line tied through the hole at the bottom of the paddle.

Monitor, well, is my dream vane. One day, ojala!

What we have here now is an old Windpilot. It is a bit like Hydrovane except the vane is vertical. Alike the older Hydro, the rudders shaft breaks. Under-engineered. I am beyond the fix-it point by now. It broke 3 times during one RTW.

So, using whatever there is while waiting for the Monitor.

b.

[Matt Johnson]

Well, this weekend I took the Dremel to the rudder post and ground down a small section to good metal. Not a great photo, but this shows what I needed to take off... it really wasn't much.




I'll take a different bit out next week and finish the lip right at the rudder.

[stillbuilding]

I would clean up and epoxy paint. Cannot see an anode in that space.

[Cheechako]

Why not a donut shaped anode? cant really see what that width is though. Is that the end of a 24" square? I'd rather see an anode than just paint. Pretty big shaft though, so you may be right. Was shaft size mentioned?

[Matt Johnson]

Originally Posted by Cheechako

Why not a donut shaped anode? cant really see what that width is though. Is that the end of a 24" square? I'd rather see an anode than just paint. Pretty big shaft though, so you may be right. Was shaft size mentioned?

It's a 2 1/2" schedule 80 stainless pipe. I will have to mount a zinc on the inside of the boat as there isn't the clearance needed outside the hull.

By epoxy paint, are you talking about something like InterProtect barrier coat?

[stillbuilding]

An anode is only useful if immersed in water. Any epoxy - jet as long as it sticks on and is thick enough to block electrical conduction.

[Cheechako]

Zinc inside the boat? You could go with flat flexible copper braided cable clamped inside on the rudder post. Then add a flat or teardrop zinc outside connected to the Braided cable with the zinc bolt. Actually this is probably a better idea than a zinc collar.
"An anode is only useful if immersed in water. Any epoxy - jet as long as it sticks on and is thick enough to block electrical conduction."
Question is: " Will this just drive the corrosion up inside the bearing....?

[afmstm]

Any coating - epoxy, paint, goop, etc is not the correct fix. Water will migrate under the coating and create an anaerobic enviornment that will encourage crevice corrosion. Don't attempt to solve a "galvanic corrosion" problem with a mechanical fix. You must use galvanic protection.

Delmarrey had it right: ""If it were mine", I'd attach a zinc on the transom below the water line with silicon bronze thru bolts into the inside and then attach a wire inside to the bolts and then perminetly to the rudder shaft allowing enough for swing and motion so it wouldn't brake. "

Use a tinned copper braid - is flexible and will remain so. Clamp to the rudder shaft with a SS hoseclamp. Verify the connection with an ohm meter (do this periodically). Make sure the zinc is close to the shaft.

Good luck!

[Matt Johnson]

That sounds like a good plan. This damage was not from my marina, but there before I bought the boat. Obviously I don't want this to happen again, so I'll tackle the external zinc problem this spring.

[donradcliffe]

Originally Posted by funjohnson

It's a 2 1/2" schedule 80 stainless pipe. I will have to mount a zinc on the inside of the boat as there isn't the clearance needed outside the hull.

By epoxy paint, are you talking about something like InterProtect barrier coat?

The wall thickness of your pipe should be 0.276"--when you are done grinding, if you've lost less than 10%, you should be OK. I'd leave it bare, except you might grind out the top of the glass in the rudder and fillet in a ring of 5200 to better seal things.

[delmarrey]

Originally Posted by donradcliffe

I'd leave it bare, except you might grind out the top of the glass in the rudder and fillet in a ring of 5200 to better seal things.

That was one of my worries above, that there might be water in the rudder core. That's one of the reasons for building with the shaft out of the water.