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losing a rudder in a narrow channel in 20 knots
The stainless steel bolt holding the lower pin for the rudder broke while we were coming into cabbage tree creek in 20 knots under sail, iT appears that the hole became slightly larger allowing the bolt to flex. Is there any definitive view on the life of ss bolts
ken22-May-2006    Edit    Delete 
Re: losing a rudder in a narrow channel in 20 knots
Ken

You must ensure that all stainless steel bolts and screws used in attaching the rudder or any other fitting to your boat are made from either 316 grade or a recognised equivalent. At the moment the most cost effective material recommended for marine use is the 316 stainless steel which is noted for giving a higher resistance to pitting and crevice corrosion in chloride environments (sea water).

Perhaps the bolt holding your lower rudder pin was undersized and therefore overstressed. If properly sized but made from the wrong material, I would have to assume the failure of the bolt to be due to stress corrosion cracking.

Do you have a photo of the rudder fitting and what size was the failed bolt?



Alastair Russell23-May-2006    Edit    Delete 
Re: losing a rudder in a narrow channel in 20 knots
It's a pity that we no longer have the structural stainless alloys which the aircraft industry used 80 or so years ago ... these problems would be far easier to address.
John23-May-2006    Edit    Delete 
Re: losing a rudder in a narrow channel in 20 knots
John

I disagree with you as I think the duplex stainless steels developed in the 1970ís solved most of the problems of the past. In our case I feel that the use of these more expensive alloys would be overkill and that properly sized 316 stainless bolts would be the way to go.

Alastair24-May-2006    Edit    Delete 
Re: losing a rudder in a narrow channel in 20 knots
I pulled the bolt out and it snapped 1/2 way down the shaft, it appears that there is some englargment of about 3/4 the depth of the hole in the transome which allowed the bolt to flex/bend. I have heard, that the fully treaded 316 ss bolts are weaker than the partially threaded bolts - no idea ? - the broken bolt appears to be 316
ken26-May-2006    Edit    Delete 

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