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dennisail · 05-12-2013, 13:44

Quote:

Originally Posted by 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.

Solid shafts I am sure are standard on many boats, but are they 87mm in diameter on a 40 foot boat? I would rather loose the rudder than rip the ass end of the boat off when hitting a large unmovable object. The corrosion started on the outside. Does corrosion suddenly not appear if the shaft is solid?

dennisail · 05-12-2013, 13:46

Thanks Ann. Will do.

Weyalan · 05-12-2013, 13:49

If it were my decision, I'd be building a new rudder entirely. I'd use a duplex stainless (Aquamet 22, or maybe 2205) rather than 316.

dennisail · 05-12-2013, 14:13

Do you have any links to data that compares 2205 to 316? I am not finding that much which is easy to interpret.

From these links it seems superior in every way. Corrosion resistance is MUCH better and it is stronger.

Grade 2205 for High Corrosion Resistance and Strength

Stainless Steel - Grade 316 (UNS S31600)

http://www.ljstar.com/technical/pdf/...05over316L.pdf

mitiempo · 05-12-2013, 14:26

Quote:

Originally Posted by dennisail

Solid shafts I am sure are standard on many boats, but are they 87mm in diameter on a 40 foot boat? I would rather loose the rudder than rip the ass end of the boat off when hitting a large unmovable object. The corrosion started on the outside. Does corrosion suddenly not appear if the shaft is solid?

Corrosion will still appear, assuming the same alloy is used. But the amount of corrosion that will allow a hollow shaft to break is not an issue on a solid shaft as there is so much more meat there in the first place.

Weyalan · 05-12-2013, 15:37

The reason I suggest replacing the rudder completely is based on an interesting experience we had with our yacht a few years ago:

Competing in a 300 nutical mile offshore race, our rudder snapped off, about 200 miles into the race, in less than ideal circumstances (not that losing a rudder is ever "ideal").

We had pulled the rudder out of the boat prior to the race and had it inspected by a local well-respected shipwright. The rudder shaft looked absolutely fine. When the rudder broke, the shaft snapped about 75mm (3") inside the blade. It was obvious from the stump of the shaft that there was quite extensive corrosion and damage to the shaft inside the rudder blade, even though the exposed part of the shaft looked fine. Hence my recommendation to replace the whole shooting match.

Duplex 2205 is quite a bit more expensive than 316, but in the total cost of a new rudder, the material cost is relatively insignificant.

I replaced the prop shaft on our boat a few years back - again I changed from 316 to 2205.

**minaret** · 05-12-2013, 19:02

Quote:

Originally Posted by mitiempo

Corrosion will still appear, assuming the same alloy is used. But the amount of corrosion that will allow a hollow shaft to break is not an issue on a solid shaft as there is so much more meat there in the first place.

And, a hollow tube is subject to buckling; solid shafts are not. This means a solid shaft will take orders of magnitude more force to fail, and when it does fail (barring corrosion), it will bend. A tube will not bend much at all, instead it will buckle. Failure will occur much, much sooner, and in a far more catastrophic way. Totally unacceptable build method for an offshore boat. Just take a piece of bar and bend it till failure (you will have to twist it in loops), then take a larger piece of tube and bend it till failure. The difference will be blatantly obvious.

dennisail · 05-12-2013, 19:16

Minaret, you are right of course. When you compare stocks of the same diameter. If the tube is made with a much larger diameter as mine is, the size makes up for the fact it is not solid. A tube is stronger than a solid round bar of the same weight, so a tube can therefore be made lighter at the same strength if it has a larger diameter.

Weyalan. The whole shaft would be replaced, so what happened to you could not happen to me even if I rebuilt the rudder.

**minaret** · 05-12-2013, 19:22

Quote:

Originally Posted by dennisail

Minaret, you are right of course. When you compare stocks of the same diameter. If the tube is made with a much larger diameter as mine is, the size makes up for the fact it is not solid. A tube is stronger than a solid round bar of the same weight, so a tube can therefore be made lighter at the same strength if it has a larger diameter.

Weyalan. The whole shaft would be replaced, so what happened to you could not happen to me even if I rebuilt the rudder.

Choose to believe what you like. All I know is that solid 3" rudder shafts are quite common in your size range. A thin walled 3 1/2" tube isn't even in the same ballpark.

dennisail · 05-12-2013, 19:27

Thanks Minaret, your opinion has been noted.

Whole yachts made fully of metal are also common in my size range.

mitiempo · 05-12-2013, 19:35

Quote:

Originally Posted by dennisail

Thanks Minaret, your opinion has been noted.

Whole yachts made fully of metal are also common in my size range.

True, but most often with solid rudder shafts.

Weyalan · 05-12-2013, 19:42

When we had our new rudder built, the naval architect we consulted told us that we should definitely use solid round bar, not tube.

drewke07 · 05-12-2013, 19:49

If it were me I'd use a Fein tool to split the fiberglass shells apart, and then a sawzall to work the foam inside. Much more control with the Fein tool. I'd use schedule 80 316 stainless pipe for the shaft, it has a thicker wall. The Aquamet 22 is a great choice if you do not have to weld to it. Be sure to use only epoxy to put it back together, and be sure to glass at least the leading edge with 17oz biax or similar. Be good to go!