Rudder question

[John Stone]

Yes, just the control lines for the windvane. I love having the space there and the accessibility to the rudder post and steering components. As much as I would like a small 20 HP diesel I like the stripped down simplicity we enjoy.

[tjr818]

John, have you thought of putting a small electric drive in there? You would still be dragging around a propeller, but you wouldn't lose as much room.

[John Stone]

I have looked into it. The propeller is not the issue. I would have a two blade folding prop with a shaft that exits just above the top of the rudder and slightly offset to the port side of the rudderpost.

The electric drive is small, as you suggest. But the batteries required take up a lot of room (you probably need at least 4) And there is no way to charge them without adding a huge solar array or going dock side for 110.

The juice is not worth the squeeze. I have had my eye on a 3 cylinder 20hp Beta but I'm reluctant to complicate the boat for something I would so seldom use. Choices. Compromises. No changes planned for now.

[Matt Cawthorne]

Thanks Matt:

Do you happen to have a photo of the setup before you started your project?

Good luck with your project.

Philip

Philip,
I have pictures on my old cell phone, but it decelerated much too quickly when it hit the cement wall and the screen cracked. I am in the process of trying to get the screen revived in order to get the pictures off. If I am successful, then I will send pictures. I can get a picture of the ring if you would like as it is on my workbench.

Matt

[Matt Cawthorne]

Matt:

What material are you using for the shaft?

Philip,

I settled on Inconel 625. It is 10 times the cost of a stainless shaft, but the stainless shaft would have needed to be passivated, and that would have made the ratio no more than 4 to one. Even if passivated, a scratch in the installation or in the fiberglass process and the passivation would have been for nothing. I took the Inconel to several machine shops that specialize in bending shafts and tubing and all refused to touch it due to the cost of the material and its reputation for being tough. In my ignorance I bought a 16 ton tubing bender and did the bending myself. It worked out fine, although I broke the 16 ton press and had to do some significant reinforcement to make it work. It was expensive, but I should never have to loose sleep worrying about crevice corrosion in my rudder again in my life, even if I live to 110 years old. In fact I am certain that in 10,000 years, some archeologist will find the rudder shaft on the bottom of the ocean next to the block of keel lead and be able to figure out what boats looked like in the 21st century! What is more, the Inconel retains most of it's strength to over 2000 degrees F so if we choose to sail up the river Styx the rudder shaft will be up to the task.

Regards,
Matt

[John Stone]

Wow Matt. Bending that was no small task. I am sure it will last a long time. Why did you rule out bronze? I'd be interested to know your thought process so I have that info when it comes time to replace the rudder on the Far Reach.

[Jim Walsh]

I retired after 38 1/2 years at Pratt & Whitney. We used lots of fairly exotic materials like Inconel, Waspalloy, and Titanium in the aerospace industry. I'm surprised you went through the expense and trouble of dealing with Inconel. It is not user friendly.

[Evergreen]

Our new rudder shaft will be made of 316 stainless.

What I am still perplexed by is the fact that our original rudder shaft showed no signs of corrosion, yet the replacement in 2007 developed extensive pitting (starting almost immediately). Both shafts were made of 304 stainless which is what Cape Dory normally used.

Oh well --- it is all water (and $) under the boat --- hopefully we will have better luck this time.

[Matt Cawthorne]

Wow Matt. Bending that was no small task. I am sure it will last a long time. Why did you rule out bronze? I'd be interested to know your thought process so I have that info when it comes time to replace the rudder on the Far Reach.

John,
Bronze can be fine provided that you are certain that it does not contain any meaningful amount of zinc. If it does, it is at risk of dezincification which turns it into brittle garbage. Most bronzes will dissolve into seawater at a rate of about .003 inches per year. This means that a 1.5 inch diameter shaft will be 1.38 inches in 20 years, worse if there are complicating factors, like flowing water. That is a reduction to about 78% of it's initial strength. This is probably not the end of the world and may be better than Stainless steel with crevice corrosion, but the older I get, the less I will be able to physically deal with catastrophy so I will want it to work. I don't have much fatigue data on Bronze so it is hard to compare it to the original part.

Regards,
Matt

[Matt Cawthorne]

I retired after 38 1/2 years at Pratt & Whitney. We used lots of fairly exotic materials like Inconel, Waspalloy, and Titanium in the aerospace industry. I'm surprised you went through the expense and trouble of dealing with Inconel. It is not user friendly.

Jim,
I may be sailing on this boat in 20 years. This rudder job is a great deal of work. I don't ever want to do it again. The inconel is expensive, but the stainless steel is the part of the old rudder that has gone south. I may be a newbie in the aerospace world with only 35 1/2 years in structural analysis, but I sort of like Inconel, despite its weight and cost. It is a really tough material, as stated earlier. It is supposed to be immune to crevice corrosion in sea water. It has a much better strength than 304 stainless and does not require passivation. It is also slightly stiffer than 304 stainless. I have had a few bad experiences with titanium in my career, but it was under consideration due to its resistance to corrosion. Cupro-nickel is a nice choice, but I do not have access to much fatigue data on it. I am always up for a discussion on alternates!

Regards,
Matt

[Matt Cawthorne]

What I am still perplexed by is the fact that our original rudder shaft showed no signs of corrosion, yet the replacement in 2007 developed extensive pitting (starting almost immediately). Both shafts were made of 304 stainless which is what Cape Dory normally used.

The correct processing is really important for stainless steel. Passivation depletes the surface of iron. It is a simple process, provided that you happen to have a tank of hot nitric acid or perhaps hot citric acid at hand. Passivation really delays the formation of the first intrusion that can start the crevice corrosion. Unfortunately, it creates a very thin layer on the surface that is resistant and it only takes a good scratch to undo the good work of the passivator. If you don't have the option of passivation, at least polish the shaft until it looks like a mirror. That has a similar, but not quite as effective impact. If you mention passivation to the maker of your new rudder and you get a blank stare or some line that implies that is is not helpful, then shop elsewhere.

Also, if you weld stainless, and don't know how do post weld processing correctly, you can get inter-granular corrosion which turns it into the equivalent of the strength of a sugar cube (that is an exaggeration, but not by much). Low carbon versions of stainless are not prone to this problem.

[Evergreen]

The new Robinhood is doing my replacement rudder. Hopefully they know what they are doing better than the last crew.