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Old 01-06-2011, 08:31 PM   #41
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RE: Rudder cracked

Quote:
timjet wrote:I've thought of that too. So far no leaks at all around the prop shafts.
Unfortuantely that doesn't indicate the absence of crevice corrosion.* It just means the seal/shaft log/packing material is in good shape. So far as I know the only way to determine if there is crevice corrosion on the portion of a prop shaft that is up in the tunnel is to pull the shaft.

I have no idea how quickly crevice corrosion can form, but in the twelve years we have owned our boat we have made it a practice to run the motors and turn the shafts at least once a month evfen if we don't take the boat out that month.* Crevice corrosion is also one reason*stainless fuel tanks are not a good idea, and why we have set up a fuel management program that*staggers the*use of our*five stainless fuel tanks and leaves each of them empty much of the time.*
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Old 01-07-2011, 03:08 AM   #42
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Rudder cracked

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Marin wrote:

*
Unfortuantely that doesn't indicate the absence of crevice corrosion.* It just means the seal/shaft log/packing material is in good shape. So far as I know the only way to determine if there is crevice corrosion on the portion of a prop shaft that is up in the tunnel is to pull the shaft.

I have no idea how quickly crevice corrosion can form, but in the twelve years we have owned our boat we have made it a practice to run the motors and turn the shafts at least once a month evfen if we don't take the boat out that month.* Crevice corrosion is also one reason*stainless fuel tanks are not a good idea, and why we have set up a fuel management program that*staggers the*use of our*five stainless fuel tanks and leaves each of them empty much of the time.*
*
I thought Crevice Corrosion was the title of a porn movie.

Crevice Corrosion can start within a matter of hours depending on the enviornment and type of stainless steel.
http://www.corrosionist.com/Pitting_..._Corrosion.htm

Exercising the shafts, prop or rudder will flush the water and prevent it form becoming stagnate, the reason crevice corrosion starts.

I adhere to the glass half full theory and consider (hope) my prop shafts in good shape.

*


-- Edited by timjet on Friday 7th of January 2011 04:10:41 AM
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Old 01-07-2011, 03:33 AM   #43
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RE: Rudder cracked

"I thought Crevice Corrosion was the title of a porn movie."

Its a problem caused by CHEAP!

Shafts and rudders of marine grade bronze are OTS , ready for anyone that will pay for them.

Same with holes in the boat , bronze seacocks are in every chandlers , yet folks install Home Depot SS choking ball valves and wonder why they seize up.

I understand why boat mfg install garbage , most folks don't know any better ,

but why an OWNER would choose cheap trash is still a mystery .
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Old 01-07-2011, 05:03 AM   #44
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RE: Rudder cracked

"*OTS "

?????
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Old 01-07-2011, 05:07 AM   #45
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Rudder cracked

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FF wrote:

Its a problem caused by CHEAP!

Same with holes in the boat , bronze seacocks are in every chandlers , yet folks install Home Depot SS choking ball valves and wonder why they seize up.

I understand why boat mfg install garbage , most folks don't know any better ,
Boat Manufactures must be competitive and in so doing sometime use less than the best materials. My boat never was intended to compete with a Fleming.

With that being said, my guess is that many boats that some people consider higher quality have the exact same rudder and shaft that I have.* My boat sat for over 2 years without being used much, and this created problems beyond just the crevice corrosion on the rudder. Had the boat been used continuously I may never have had to deal with CC.

Buying marine grade materials is no guarantee of quality. I'm replacing 2 marine grade ball valves, Buck Alagonquin, because the stem that connects the handle to the ball valve broke. Increasing the diameter of that stem by a 16th of an inch probably with have averted the problem.

A proper thru hull will avoid the stem problem and others as well. I didn't want to put 4 more holes in the bottom or have to deal with fabricating a backing plate.

I'm headed down to the boat today magnet in hand to check the prop shafts. I'll post pictures of the rudder repair next week. Incidentally the shaft on the rudder being repaired with be replaced with a shaft made of aquamet 22, a higher corrosive resistant SS especially designed to resist CC.
http://www.aquamet.com/aquamet22.nxg

*


-- Edited by timjet on Friday 7th of January 2011 06:16:10 AM
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Old 01-07-2011, 05:33 AM   #46
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RE: Rudder cracked

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FF wrote:Its a problem caused by CHEAP!


Shafts and rudders of marine grade bronze are OTS , ready for anyone that will pay for them.


I understand why boat mfg install garbage , most folks don't know any better ,

but why an OWNER would choose cheap trash is still a mystery .
It is a problem caused by letting boats sit in the water for extended periods without being used.

Those shelves must be in antique shops. Bronze shafts are no longer used because for the same horsepower they require larger sizes, more weight, much more cost, and create their own problems related to wear and galvanic corrosion. All of those issues have made bronze shafts obsolete. Even if one were to demand bronze and pay the large premium, there would be no life cycle cost advantage to the builder or the owner. Time moves on and it doesn't move on bronze shafting.

The designer and builder select materials to provide the best balance between price and utility. They are not in business to intentionally deliver junk.

Why an owner would demand obsolete and expensive "solutions" to problems that are easily and economically managed by user technique is the real mystery.
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Old 01-07-2011, 06:06 AM   #47
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RE: Rudder cracked

Rick nailed it. User technique and limitations. No matter how good a design and materials used if not used properly or adhered to it's limitations it will be junk.
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Old 01-07-2011, 12:03 PM   #48
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RE: Rudder cracked

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jleonard wrote:

"*OTS "

?????
I'm guessing FF means "off-the-shelf."

*
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Old 01-07-2011, 12:09 PM   #49
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RE: Rudder cracked

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Marin wrote:I'm guessing FF means "off-the-shelf."
*Yeah, but it would have to be NOS.*
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Old 01-09-2011, 07:14 AM   #50
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RE: Rudder cracked

it would have to be NOS

Most of my marine contacts can provide Bronze in a couple of grades as well as SS in a few.

OTS is Off The Shelf usually the cheapest & most reliable source.

NOS is New Old Stock , something in a warehouse for almost forever , but still a delight.

If you really need a cylinder head for your 41 Crosley 2 cylinder engine , NOS is a gift from the Gods!
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Old 01-22-2011, 05:17 AM   #51
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Rudder cracked

OK guys, I got the rudders back yesterday and if my help is available, will install them today.
I ended up having to install the shafts in both rudders because of crevice corrosion.

On both rudders the machinist cut out the existing shaft and inserted a new one with pins installed to prevent the shaft from rotating on the rudder. He then welded up the shaft into the rudder.

On the cracked one he removed a little more material but as I understand it both were pretty much done the same way. Recall that the cracks on the one were where the shaft enters the rudder.

Pictures show the cracked rudder repaired and the old shafts.

The cost to do this was about 2/3 the cost of replacing the rudders with new, but I opted to have them repaired because the shafts are made of Aquamet 22 and are more resistant to crevice corrosion. The new replacement shafts would have been the same as the original.

-- Edited by timjet on Saturday 22nd of January 2011 06:18:58 AM

-- Edited by timjet on Saturday 22nd of January 2011 06:20:26 AM
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