Rudder cracked

[markpierce]

Glad that's solved.

 

[FF]

Yup, I'm gonna order a new one tomorrow.



KEEP the damaged one on board as a spare.

Should you somehow damage the new one ,

a quick tide swop will have you underway , not at the mercy of the boat yard pirates!

 

[sunchaser]

Assuming you still have a bonding issue, what are you going to do to obviate that problem?

Does this diagnosis from the shop mean your other rudder may have similar lurking issues with corrosion? If in doubt, I'd buy a new one and repair the old as an immediate backup. I just sprung a weep in an exhaust mixing elbow. The other looked fine but I changed them both anyway.

 

[Doc]

I am going to guess that the pitting in the shaft was CC, which is more likely to occur with an inferior metal blend. I would not buy from the same supplier. Yours is not the first Carver to have had bad CC with the prop or rudder shafts.

 

[timjet]

Crevice Corrosion, I thought you guys just made that up. Well its alive and well and on my boat. My research and correct me if Im wrong indicates that crevice corrosion is most prevalent where water stagnates like in an inactive rudder log. The chlorine in sea water reacts with oxygen and creates a corrosive environment that pits stainless steel. I found out that the ss rudder shaft is magnetic indicating that it is of lesser quality, probably 400 series?? However, according to Carver, Marine Associates, and the prop shop, the lower quality of the shaft used on my rudders is used on many production boats with good results. Carver suggested that perhaps the boat had not been used much recently and he was correct in that assessment. Exercising the rudders by turning the helm wheel will flush out the stagnate water in the rudder logs delaying or preventing the formation of crevice corrosion, even if just done at the slip.


With this knowledge I called the prop shop to stop them from having a new rudder shipped. Hopefully I called in time. The prop shop will repair the rudder with a new ss shaft of higher quality though this is no guarantee that it wont happen again.


Tom, I know the other rudder is affected with CC as well but not as bad. Before having this knowledge I was just going to re-install it. Im now going to have the prop shop look at it and hopefully they can just cut out the section with the CC and machine in a new section. The only corrosion on either rudder is located at the point where the shaft passes through the rudder log, so I dont think I have any electrical induced corrosion, galvanic corrosion?? The rudder logs when they were removed had some green stuff around them and so did the bonding wires, but once cleaned the rudder logs looked good.


A new checklist item will now be entered on my boat checklist - exercise the rudders.

 

[jleonard]

"A new checklist item will now be entered on my boat checklist - exercise the rudders."

If you have grandchildren that come aboard you won't have to worry about this task. LOL

 

[Doc]

Exercise the prop shafts too. My buddy's Carver had CC pitting inside the cutlass bearings and they could not be repaired. When this was going on Carver accused him of not running his boat often enough...which was true. He claims, however, that he started the boat almost weekly and put it in gear to spin the shafts.

 

[timjet]

jleonard wrote:
If you have grandchildren that come aboard you won't have to worry about this task. LOL

Jay, I showed this to my wife as we have 3 grandchildren that aren't quite old enough but soon will be. We both got a chuckle out of it. I can just see all 3 of em up on the bridge turning the wheel and blowing the horn. What fun.

*

 

[timjet]

Doc wrote:

Exercise the prop shafts too. My buddy's Carver had CC pitting inside the cutlass bearings and they could not be repaired. When this was going on Carver accused him of not running his boat often enough...which was true. He claims, however, that he started the boat almost weekly and put it in gear to spin the shafts.

I've thought of that too. So far no leaks at all around the prop shafts.

*

 

[RickB]

"So far no leaks at all around the prop shafts."

Which just means that in way of the seal at least, there is no water movement, it is stagnant which means the oxygen is depleted and that is what causes crevice corrosion.

You can't change nature, the materials on your boat*are trying to return to*their original state. The only thing that can slow the process is the contents of your bank account.

 

[Marin]

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.*

 

[timjet]

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_Crevice_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

 

[FF]

"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 .

 

[jleonard]

"*OTS "

?????

 

[timjet]

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

 

[RickB]

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.

 

[timjet]

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.

 

[Marin]

jleonard wrote:

"*OTS "

?????

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

*

 

[RickB]

Marin wrote:I'm guessing FF means "off-the-shelf."

*Yeah, but it would have to be NOS.*

 

[FF]

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!

 

[timjet]

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