Stainless Rudder Stock Needs Replacing In Foam Core Rudder?

[dennisail]

Hey guys. I pulled the rudder from my Hunter Legend 40.5. It has crevice corrosion at the base of the shaft where it enters the rudder. So I need a new shaft or whole new rudder. I am looking here to seek opinions on the best course in action.

Options are, cut apart the rudder and replace the SS shaft (or maybe go to a composite shaft), then glue the rudder back together ad re-laminate. If you suggest this method please explain the rough details of this suggestion. IE where is the best place to slice it up etc to make it easiest to get back together straight.

Another option is to build a whole new rudder, possibly with composite shaft. Note my particular model of boat usually did come with a glass shaft and the fact that it is stainless is actually odd. I do fancy building a boat one day so this might be good project, however I do really want to get this out out sailing again soon.

The rudder is foam and glass and does not appear to be water logged as no water came out of any holes I drilled in it. Some water did slowly drip out where the shaft goes into the rudder. But I even drilled holes around the shaft area from the rudder skins and no water came out, so the water must be fairly localized around the rudder post entry.

It may be hard to see from the pics but it is quite big. Its a 2 person lift and the blade is 1140 x 860 x 118mm, and the post sticks out 930mm and is around 87mm tube 6mm thick.

Any suggestions?

Click for pics

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[colemj]

That looks like it could be galvanic corrosion and not crevice corrosion. If galvanic, you need to find out why and correct that.

Mark

[Stumble]

It looks like a combination of pitting, and poltice corrosion, with some crevice corrosion thrown in for fun. I wouldn't be suprized if when that thing is examined there are hidden defects running thru it. All three tend to go together, and can actually create localized galvanic corrosion (between the passive and non-passive stainless). This is exacally why I hate stainless below the waterline.

I don't think there are many options here. That shaft needs replacing, the only question is with what. Composites would be an option, so would a titanium shaft (about the same as 316 stainless).

[dennisail]

Yeah either way. I would not trust the shaft for more than bay sailing anymore and I am sure more defects go undetected.

When you say titanium is the same as 316 stainless, by what measure is it the same? Cost? I would have thought cost would be astronomical.

[mitiempo]

Titanium is not the same as stainless. One should never be used underwater - stainless - due to the crevice corrosion that you experienced. Titanium does not suffer from this.

[dennisail]

Yeah if the whole boat was titanium it would be better too, but the fact is the vast majority of rudder stocks are 316. This one lasted 20 years and who knows how close it actually is to breaking, might last another 20. These days there are a a few better alternatives in various grades of stainless which are better than 316.

[djmarchand]

Well, whether you replace with stainless, titanium, frp, Kevlar, or ? I would try to save the fiberglass shells of the rudder. I would take a sawsall and split it, cutting in from each side, working my way around the armature (the ss plates that the rudder shaft is welded to).

Once you get a 6" deep cut all around it you should be able to work a hand saw in and cut through to the other side. Once it splits apart then you can dig out the shaft, armature and the foam.

Then if you are using stainless steel shafting weld up a new armature. I would use heavier plate than Hunter used and make sure the welder knows his stuff. Seems like there were several rudders lost this year in the Caribbean rallies, one being a Hunter and two Catalinas.

Then shape two foam halves to match and bond them to the shells with thickened polyester. Then bond the two halves together around the armature with thickened polyester. Taper back the peripheral joint and cover it with several layers of fiberglass tape and polyester.

You could do the same thing with a Kevlar or FRP shaft, but you will have to build an armature out of Kevlar/glass layup.

I will bet that titanium will be prohibitive, but should last forever if you do it.

David

[mitiempo]

The only stainless I can think of that would be a better choice than 316 is Aquamet 22, probably the best current choice for shafting. Not sure of its welding issues though.

If you are going to the trouble of rebuilding the rudder use epoxy not polyester. Much better choice, especially underwater.

[minaret]

Thought about replacing with a proper solid shaft instead of that thin walled pipe they call a shaft?

[Ocean Diamond 2]

Hi dennisail,

I have a solid rudder stock and rudder off an elan not doing anything.
If you could use it is going cheap. Its about 7 years old.
Can even organise delivery.
Stock length 840mm approx
shaft Dia; 68mm approx,
Bearings dia; 90mm approx
Rudder height 1400mm
Rudder width 550mm
I know its not the same size but Im sure with a good shipwright the shaft would be a lot stronger than the pipe.
The rusty water was from beer cans left by shipwright in the wooden box thats been in my back yard.

[rtbates]

How about a silicon bronze shaft?

[dennisail]

Thanks everyone

djmarch, The hunter that lost its rudder. I bet it was a fiberglass shaft. Mine was made in stainless, either because the owner did not like fiberglass or perhaps it broke already. Fiberglass was the standard material for my make of boat. Thanks for the tip on how to cut it apart. I would use epoxy though.

Minaret, as for a solid stock. Maybe you are lost in the imperial and metric world. The existing stock is 87mm thats 3.5". A solid metal stock of this size for my style of boat would be overkill and weigh 190lbs or 87kg! Its this big because a fiberglass tube was deemed strong enough in this size!

Melani. Thanks for the offer, but that is not even going to come close to being an easy replacement. The critical sizes are have too much discrepancy.

Silicone bronze sounds interesting, but I think stainless will do another 20 years.

[dennisail]

Dissecting the old rudder?

Anyway, I am still trying to decide on the best way to rip this rudder apart so that it can be salvaged. I want to be confident that when I do it I am doing right. I have been told several different ways.

Skinning one side by removing the laminate, then digging down to the metal shaft and tabs. This sounds like it would end badly unless the skin is not well bonded?

Chopping in from one side above the shaft and tabs. This should leave enough of the skin to fair over. Once again even if I can use a drill to feel out where the tabs are, it will still be pretty hard to rip the metal part out if its recessed down a hole I cut in the face of the rudder.

Splitting the rudder in half with a sawzall so it comes apart in 2 halves. This should expose the tabbing and it will glue back together easily. The sawzall should be able to get around the tabbing by feel. Seems to have the least drawbacks.

The prob is I have no idea what the tabbing might look like so as to choose the best method. If the tabs are just laying flat as compared the rudder face the sawzall method would be best for sure. But if any tabbing is perpendicular to this plane the rudder may not come apart.

[minaret]

No Sawzall needed, just use a cutting disc to split it open. It's easy, I've done many.

Believe me, a solid shaft is not overkill. That thin walled pipe was never OK, and you wouldn't be here now if they'd built it right in the first place. Solid shafts are standard on boats of any degree of quality. Tab welds also tend to fail much faster on material like this.


Silicon bronze would be a poor choice of material, too soft and easy to bend.

[JPA Cate]

I have a suggestion for before you start cutting it up: Make a template so you can get the shapes correct when you put it back together.

Good luck with your project.

Ann