Rudder check

[daletournier]

How many pull their rudders to have a look?

I'm on the hard in Trinidad, there was a little slop in the rudder bearings, not huge but abit. I've got quite few miles to go to get home so I thought I'd change them.

I was surprised to find quite abit of what looks like crevice corrosion on the rudder post, just above where it enters the rudder.

This area sits directly under what Catalina calls a thrust bearing, just a plastic ring that has no load on it, it just sits between the lower rudder bearing and the rudder.

I'm in the process of fitting a new rudder, I'm not brave enough to risk it, the load that rudder is under at times is impressive.

Any ideas what caused this? All my other undef water parts are fine, zincs last me over a year comfortably.

Attachment 200504

[Nicholson58]

Hard to tell from the photos. Are you talking about the vertical lines or is there a transverse crack at the metal/glass interface? Which yard are you in? Get on, the morning net and ask for opinions and help. There are a lot of returning cruisers there now who can assist or also direct you to experienced mechanical service. The rigger, Jonas, might know. Also ask Lee on Alegro at Power Boat. He is near Budget Marine. We will be back early November, ROXY. If it’s a production boat contact the manufacturer.

[daletournier]

Originally Posted by Nicholson58

Hard to tell from the photos. Are you talking about the vertical lines or is there a transverse crack at the metal/glass interface? Which yard are you in? Get on, the morning net and ask for opinions and help. There are a lot of returning cruisers there now who can assist or also direct you to experienced mechanical service. The rigger, Jonas, might know. Also ask Lee on Alegro at Power Boat. He is near Budget Marine. We will be back early November, ROXY. If it’s a production boat contact the manufacturer.

Hi ,I'm at Powerboats, I walk past your boat everyday, nice boat.

I'm talking about the pitting in the shaft, some of it is 3mm deep.

It looks like crevice corrosion which I find hard to understand how that's possible, you would think plenty of fresh salt water flowing past would prevent that from happening. As mentioned its directly where that big blue washer sits, but I cant see how that effects it.

I read somewhere that powerboats often suffer from pitting like this ,something to do with prop cavitation??

Jonas is doing some work for me now, I did show him.

[daletournier]

Close up shot.

[Jim Cate]

Dale, you might try a PM to Boat Poker if he doesn't show up soon. He's pretty switched on with respect to corrosion issues.

My guess is that the thrust bearing is interfering with water flow in that area and thus promoting crevice corrosion... but that's definitely in the guess category.

And I think you are very wise to replace at this time!

Jim

[DeepFrz]

The problem with crevice corrosion, as I understand it, is that there is no way to tell how deep the problem goes so I think you are right in replacing it. Why it happens is because it is stainless steel below the water line and the plastic probably prevents water flow to that small area. That of course is a guess and I'm certainly not a metallurgist.

Hahaha...I posted just after Jim with pretty much the same opinion.

[Checkswrecks]

Originally Posted by Jim Cate

My guess is that the thrust bearing is interfering with water flow in that area and thus promoting crevice corrosion... but that's definitely in the guess category.

The only way to know the depth without good lab equipment is to use a grinder and start grinding till hitting clean metal. Yours looks deep enough that the structural integrity likely would be badly affected by this.

A good welder can then lay in new material but it would need to be the same stainless as the original, some stainless can not be welded to begin with, and the welding would likely burn out the resin from the adjacent fiberglass.

Bummer

[daletournier]

I have know idea but at a guess I had thought and agree with the above suggestions that the washer that's impeding water flow is somehow causing the issue.

Thanks.

[wingssail]

Originally Posted by daletournier

How many pull their rudders to have a look?...Any ideas what caused this? All my other undef water parts are fine, zincs last me over a year comfortably...

Attachment 200504Attachment 200505Attachment 200506

I don't know what causes this but it is not unheard of.

We've had similar corrosion on our aluminum rudder stock. Our sister ship's rudder stock broke off during a Pacific Crossing, which concerned us enough to check ours and we found alarming corrosion.

You can see in our photo that we had 2-3mm pits. Our machine shop ground out the area to a depth to 3/8 inch and found good metal there. They built up the pitted area and resurfaced it. They also inserted into the tube a tight fitting, solid, aluminum rod which extended several inches above and below the top of the rudder itself.

We replaced the bearings.

That was halfway around the world. This repair has held.

I also engineered a good emergency rudder system, which we never implemented.

BTW, we have no washer which would impede the water flow. The pitted area was exposed to the seawater.

Before and after:

[Paul L]

I've seen corrosion like this on a number boats just as the shaft enters the hull. Dropping your rudder is the only way you'll discover it, so it probably a .ot more common than most think. We drop ours every 2-3 years, just to check on everything.

[Nicholson58]

Little local galvanic cells. Once a pit starts the situation is enhanced due to poor circulation at the bottom of the hole. If you had a skeg I would say not so bad. With cantilevered spade the worst load is at the flaws. There is combination bending and torsion. Loading is reversing and cyclic, leading to fatigue. It could snap off any time from a deep crack you don’t see. This happened to us crewing on a Morgan 37 Heritage One Ton on Lake Erie. Always in fresh water but a fatigue crack let go at exactly that spot on a 5” stock. I would get serious with Benetou. Maybe they can get you some help. There are a lot of them. Has any other owner noticed? Can you find a used one?

[daletournier]

Originally Posted by wingssail

I don't know what causes this but it is not unheard of.

We've had similar corrosion on our aluminum rudder stock. Our sister ship's rudder stock broke off during a Pacific Crossing, which concerned us enough to check ours and we found alarming corrosion.

You can see in our photo that we had 2-3mm pits. Our machine shop ground out the area to a depth to 3/8 inch and found good metal there. They built up the pitted area and resurfaced it. They also inserted into the tube a tight fitting, solid, aluminum rod which extended several inches above and below the top of the rudder itself.

We replaced the bearings.

That was halfway around the world. This repair has held.

I also engineered a good emergency rudder system, which we never implemented.

BTW, we have no washer which would impede the water flow. The pitted area was exposed to the seawater.

Before and after:

I think very few check their rudders. Theres a couple of 100 boats on the hard here in Trinidad, being curious as I walk past boats with spade rudders and twin rudders I've been giving them a little wobble. I would say 8 out of ten have alot of play in them, a couple are extraordinarily bad. I can see similar pitting on a hunter rudder shaft as it has no washer allowing me to view it (probably blows my delrin washer theory), I bet you most have know idea what's going on with their rudders.

[daletournier]

Originally Posted by Nicholson58

Little local galvanic cells. Once a pit starts the situation is enhanced due to poor circulation at the bottom of the hole. If you had a skeg I would say not so bad. With cantilevered spade the worst load is at the flaws. There is combination bending and torsion. Loading is reversing and cyclic, leading to fatigue. It could snap off any time from a deep crack you don’t see. This happened to us crewing on a Morgan 37 Heritage One Ton on Lake Erie. Always in fresh water but a fatigue crack let go at exactly that spot on a 5” stock. I would get serious with Benetou. Maybe they can get you some help. There are a lot of them. Has any other owner noticed? Can you find a used one?

I lucked out. I sourced a brand new rudder and bearings still in the crate for half price.

He purchased it to replace his rudder because it had water in it, before getting around to fitting it his boat was written of in a hurricane a couple of years back.....sometimes you get lucky (I mean me ,not him).

I've got a Catalina 470.

[Nicholson58]

BTW. I got all of my replacement plastic rudder bearings from IGUS. At the time, I was still working in machine building. They sampled me the bearings at very low cost. They will have plain, flanged and washers. If you go through normal marine suppliers these can be insane.

Don’t tell any merchants ever that you are shopping for a boat part. If asked, farm implements.


https://www.igus.com/iglide/plain-bearing Many materials are available.

[daletournier]

A set of bearings from Catalina is close to $1,000.

Originally Posted by Nicholson58

BTW. I got all of my replacement plastic rudder bearings from IGUS. At the time, I was still working in machine building. They sampled me the bearings at very low cost. They will have plain, flanged and washers. If you go through normal marine suppliers these can be insane.

Don’t tell any merchants ever that you are shopping for a boat part. If asked, farm implements.


https://www.igus.com/iglide/plain-bearing Many materials are available.