[Rhodes22-list] Broken diamondboard centerboard

[ROGER PIHLAJA]

Hi David,

Is the pivot pin magnetic?  It shouldn't be.  There are two types of stainless steel alloys, martensitic (MAR) and austenitic (AUS).  MAR alloys are magnetic, work harden to very high strength and brittle and are not as corrosion resistant.  When a MAR alloy work hardens and cracks, you get ferrous carbide crystals along the fracture planes.  Ferrous carbide is a ceramic, very hard, brittle, and glassy.   Usually, a pivot pin would be made of an AUS alloy.  AUS alloys are nonmagnetic, are not as subject to work hardening, and are more corrosion resistant.  If the pivot pin is magnetic; then, the wrong stainless steel alloy was used.  Typical AUS stainless steel alloys used in marine applications include types 304 and 316.

With the pivot pin cracked like that, is there a leak into the bilge?

I still stand by my hypothesis that your boat was backed into something with the centerboard down.

Roger Pihlaja
S/V Dynamic Equilibrium
1978  Sanford, MI


________________________________
From: Rhodes22-list <rhodes22-list-bounces at rhodes22.org> on behalf of DAVID BERG via Rhodes22-list <rhodes22-list at rhodes22.org>
Sent: Monday, August 3, 2026 1:14 PM
To: rhodes22-list at rhodes22.org <rhodes22-list at rhodes22.org>
Subject: Re: [Rhodes22-list] Broken diamondboard centerboard

I pulled the boat out and was cleaning the bottom before taking it to the boatyard. I found the remains of the pivot pin and the broken corner of the CB.

It is certain that the pivot had failed some time ago. I can't identify what it is (was) made of. I was thinking it was going to be stainless steel. It seems almost like stone in its hardness, and obviously brittle. Does anyone know what this is made from?

Dave
Blue Loon
1996/2003
Minneapolis, MN

[ Sent From rhodes22.net ]

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