ss rudder stock fracture

[Zanshin]

I hope that someone here might be able to help me or point me in the correct direction where I might find expert advice. I'll accept rebukes if I am out of line in this forum as well.

I recently had a solid stainless steel rudder stock fail and break off at sea. It broke at the point where it enters the hull and I have some closeup detailed photographs of the remaining rudder stock that I would like to have expert opinions on. Losing a rudder at sea in a fin-keel sailboat was not a fun experience at the boat has absolutely no direcdtional stability. I was just beginning my circumnavigation and must admit that I have more than a slight feeling of unease. If galvanic corrosion or some other avoidable condition caused the rudder to fail that would be one thing, but what if the rudder stock material is not to specifications or the rudder is mis-engineered, then my replacement rudder might fail when 800 miles out to sea instead of 8. I was lucky that my incident occurred in mild conditions and when the rudder wasn't under much stress - but that probably won't be the case should that occur again.
I'd appreciate pointers on where I might get some advice, and will post links to 2 of the pictures in this post, just in case someone here might be willing to assist. At the least, the pictures might provoke some discussion amongst the pundits.

Closeup of stock after cursory cleaning

Taken from directly below upon haulout showing rudder through-hull

 

[unclesyd]

Been there and done that in the local pass 15' following seas 6 knot tidal current. 45 ft single engine boat.

It looks like some type of torsional failure enhanced by some corrosion. It appears to be copper plated at on part of fracture surface. Prior to cleaning it look like rust on the periphery of the fracture.

Can you comeback with the type SS and the age for the post.

What is the size of the shaft?

Is there mixed metal in the stuffing box?

What size is the boat.

 

[Zanshin]

The boat is a 4-year old 43 foot Jeanneau. I purchased the boat 6 months ago and the survey showed fibreglass damage to the bottom of the rudder and loose shaft bearings, both of which were repaired to my surveyor's satisfaction. The boat is an ex-charter one that has probably seen a lot of abuse, but most likely never seen bad weather. The whole area around and within the arc of the rudder on the bottom of the hull shows slight evidence of rust. The zinc anode on the propellor shaft was only 1/3 gone, but it was loose enough around the shaft so that I think it might only have been in effective contact part of the time, if at all.

The copper deposits bothered me as well. But the photos were taken 4 weeks after the incident; I have been in a marina in the Caribbean waiting on the new rudder for that time. The current ablative antifouling paint is cuprous oxide based. My initial thoughts are that the remaining part of the rudder stock was acting as a cathode for an (as yet undiscovered) electrical "leak" on the boat. I will be checking for a DC or AC drain and for proper grounding this weekend.

I've asked the manufacturer for the rudder stock specifications but haven't heard back from them. The stock is probably 2 1/2 inches in diameter.

 

[EdStainless]

photos? It may be that you had some crevice corrosion at the seal that contributed to this. If so, then you are in good shape. Replace everything and go. If there is no sign of crevice corrosion then you need to be more concerned about the actual stresses on the rudder.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Zanshin]

Hello EdStainless - were the first 2 pictures in the original post not visible to you? The closeup can be viewed at

http://i31.photobucket.com/albums/c390/ShiroAZ/StockCloseup_small.jpg

I can also post more, but as the originals are 4Mb apiece I can't post them, and if I resize the images in order to be small enough to be manageable the details are probably going to go away.

 

[HEC]

Zanshin,
The damage may have been caused during the vessels life as a hire. As you state there was damage to the bottom of the rudder blade. It is possible that the craft has been run aground and in the process of getting off the rudder has been over stressed. The stress could be from direct bending i.e. a blow from the side or torsion i.e. turning the blade while it is stuck in the sand. This could have created local fractures that have eventually caused the failure. From the photo the fracture surface seems quite polished without much evidence of brittle fracture face. This suggests that the fracture has been "working" for some time. The Jeanneau has a balanced rudder without a skeg, witht the loose rudder bearings there may have been some flutter occuring.
Further thought along the fluttering line, as a charter vessel it has probably spent excesive time under motor, with the result of more turbulence off the prop resulting in excessive fluttering (torsional vibration of the rudder blade).
Just a few random thoughts. The conclusion is another failure of the shaft is unlikely.
Happy Sailing.. A Jeanneau 43 sounds like a nice way to travel.

Mark Hutton