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Salt sailors, checked the lower pintle lately?

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Leon Sisson
Master Marine Consultant

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USA
1889 Posts

Initially Posted - 06/16/2002 : 21:34:13

I knew the lower pintle was cracked. It was that way when I got the boat. Since I plan to replace the entire rudder with a balanced one, I decided to postpone doing anything about the cracked lower pintle pin. (If it's lasted this long ...) Today, I took the boat to a nearby sand bar where I gently run it aground and wade around it to clean the accumulated bottom growth just below the waterline. While I was getting the anchor set after touching bottom with the swing keel raised, the wind caused the boat to pivot, and allowed the rudder to hit bottom. I didn't pay it any attention until I was climbing back up the boarding ladder. I noticed the rudder at an odd angle, and just figured it had been bumped up out of the gudgeons by touching bottom. However, the bottom pintle seem very reluctant to slide back into the gudgeon. Much to my chagrin, upon closer inspection here's what I found:

<img src="http://www.trailersailor.com/uploads/c25_pintle_01.jpg" border=0>

Fortunately, I was only about a half mile from home, and what's left of the pintle pin still worked enough to motor back to the dock. The new pintles for the balanced rudder project are already sitting in the shop, so the old rudder can be patched up quickly. Just thought I'd mention this, in case any of you who keep your older C-25 in salt water are also following the same popular "out of sight--out of mind", "yeah, I'll do something about that later" and "if it ain't broke, don't mess with it" rudder maintenance schedule.

-- Leon Sisson

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OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 06/17/2002 : 12:54:03

Here's a great example of how valuable this forum can be.

Leon, I assume there's rust on the pintles do to saltwater?

Thanks for the extra time and effort involved in taking and posting the pics!

Steve Madsen
#2428
OJ (Ode to Joy)

Edited by - OJ on 06/17/2002 12:56:05

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Leon Sisson
Master Marine Consultant

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USA
1889 Posts

Response Posted - 06/17/2002 : 22:17:05

Steve and others,

Re: "I assume there's rust on the pintles due to saltwater?"

Based on my limited knowledge of metalurgy, this is an example of one of the less endearing characteristics of stainless steel -- crevice corrosion. See the hairline cracks on the exterior surfaces of the pieces of the pin? That's all I noticed before it failed. As you can see, each crack represents a plane of failure perpendicular to the surface. This is just the opposite of what one might expect based on observations of carbon steel rusting. In carbon steel, the fault lines are parallel to, and close to, the surface. In carbon steel rust, what you see is what you get, an ugly surface, but leaving strong solid metal underneath.

This part, although rotten to the core, didn't look all that bad on the outside, right up until it suddenly crumbled. It just showed some light staining, and hairline cracks almost too fine to spot with the naked eye.

As I understand it, so called "stainless steel" needs constant exposure to oxygen to prevent rust from getting a foothold. Once again, just the opposite of carbon steel. I believe this is more of a problem with the common 302/304 alloys than with the slightly weaker and much more expensive 316 material. Frequent submersion in seawater deprives the stainless steel of oxygen, as well as subjecting any surface flaws to corrosive invasion by salt into the metal's grain structure.

This should also help us to remember to replace those stainless steel bolts that support the swing keel pivot and cable attachment, right?
I'm a big fan of silicon bronze below the waterline. In fact, I've installed all-bronze backup supports for my swing keel pivot bearings. (How's that for paranoid?<img src=icon_smile.gif border=0 align=middle>)

As an additional aside, I'll be installing cast-in glass filled epoxy resin bushings in the rudder stock at all four pintle bolts. When I removed the old pintles and drilled out the 1/4" holes to 1/2" in preparation for filling, the wood at the more highly stressed lower pintle was only slightly damaged from saltwater, a weak natural wood preservative. At the upper holes, the plywood surrounding the bolts was like black oatmeal from rainwater intrusion.

-- Leon Sisson

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Phredde
Navigator

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125 Posts

Response Posted - 06/18/2002 : 20:48:57

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote> . (If it's lasted this long ...) <hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>

That is me to a tee, I'll be checking mine this week, thanks!

Phredde
Catalina 25
San Francisco

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