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Rudder Cheek blowout!


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I come before you humbled yet again.  Perhaps I'm pushing this boat a bit harder than the previous owner?

 

During a gybe yesterday at about 8 knots, I heard a POP and lost most of my steerage.  We quickly got the motor going and dropped the sails.  We anchored up in the lee of an island, secured the blade and motored home. We may have hit something - there has been a bit of debris out there this week due to big storms.  Great!   Another project!

 

I'm guessing the lower gudgeon is designed to break before the rudder blade in the event of an impact.

 

The rudder blade blew out the back of the lower gudgeon and twisted the upper gudgeon severely enough that I think I need to reglass it as well.  The cheek was badly torn on one side.  There are several pictures here:   https://imgur.com/a/V0pZ4

 

I need short term fix to get up and running for the long weekend coming up.  A longer term fix can be discussed further down this thread.  I'm not sure of the process to rebuild this thing, but am certainly willing to try.  How would you tackle this?  

 

The rudder blade is undamaged.

 

The drawings call for 200 strands of gunstock for each gudgeon, 1135 triax for the cheeks and 3 layers of triax between the upper gudgeon and tiller.

 

I'll post this on boatdesign.net also, but I think a lot of you guys have actually done this work on this type of boat, so I figured this to be the best place!

 

ttUbxbC.jpg

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I've blown the bottom gudgeon off on of my rudders. I would suggest they they should be bloody strong, not engineered to break before rudder. Mine are anyway. I have a heap of carbon unis tying mine on. Can't remember how many just know it's twice as much as required as I ordered too much by mistake, chucked it all on.

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Been there done that twice. Once because of stupid underbuild and second time because I hit a rock. That time I missed a race but the boat was back in working order within a week.

 

By the looks of it I don't think you hit something. I think this is a case of too weak.

 

Remove damaged laminate (angle grinder and 40 grit 'paper' comes to mind). Rebuild and make it strong enough. You need a 'bandage' of fibres holding it together between the pin and the sleeve.

 

Idealy you should have fibres forming a figure '8' with the rudder sleeve in one loop and the bolt (pin) in the other loop + fibres wraped around a whole lot inone loop. The intent is to create something that can take shear and bending.

 

Well, I guess ideally you should do something a la Marström in carbon prepreg (50% of fibres parallell to rudder cord and 50% at +/- 45 degrees to cord) but since that is out of reach for most of us mere mortals...

 

Reinforce the one that did not break this time.

 

/Martin

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Thanks Fellas.

 

My current plan is to:
1)Grind off the paint 
2) Wax the rudder blade, cover it in wax paper and slide it back into the rudder head to get everything lined up. 
3) Repair the cracks with epoxy and 404 filler.
4) re-glass the Gudgeons.
5) Cut away the thin cheek panels, and glass in new ones.
6) Fair and paint.

Anybody want to add/remove steps here?

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I have also split my rudder cassette case and, on another occasion also ripped the gudgeons of the back of my float (trimaran) both somewhat hair raising experiences. There is a LOT of stress through the rudders when you are going fast. for your steps; when ever you are saying "glass" I'd be using carbon uni and bi-directional with a 60:40 split respectively - also beef up the one that didn't break to the same standard.  

 

My 2c woth...

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We discussed this build here a few years back circa 2009-10.  I recall a few quite good drawings being put forward- can't remember if it was Booger (ex Borderline) or the Charleston brothers who put up the best pics.  If your rudders are well built and of carbon then don't bother replacing the side panels.  The rudders themselves should be strong enough to span the gudgeons - at last that's my view.  I always remember U2 having a continuous issue with cracking the case sides and in the end he just cut the back of them out to allow them to twist with the rudder - problem dissapeared.  I built my cases for Euphoria merely as a box where the leading and trailing edges act as a guide to hold the gudgeons together and then I laminated a diagonal strut in case someone pulls on the aft edge - again not much torsional stiffness between the top and bottom gudgeons.  However the rudders were built by Tim Willetts and are seriously strong carbon jobbies. 

 

From memory the detail I liked the best was laminated triax (or quadrax) plates on top of each other with the gudgeon bearing tube set in a front drilled slot or hole and the aft feathered out as it connects to the case.  Follow up with shedloads of carbon tow or uni-tape wrapped forward and aft around the whole thing, followed by shed loads of carbon wrapped crosswise around the cap between gudgeon pin and case - rinse and repeat!  Probably have some sketches it on my home PC so will dig them up later.  Use a rod the same dia. as the gudgeon pins long enough to set them both in line so they don't bind when you turn.  Look at building in some ackerman into your tiller bar connections as well so that the two boards aren't fighting each other.

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Getting the uni's between the gudgeon and the rudder cassette is the easy part. Solving the sideways load, which puts all of that carbon into a peel failure mode, is the tricky part. As suggested above have flat plate holding the gudgeon tube on is good. Also wrap the uni's around the opposite way, at 90˚ to the major uni's, then cover what you can in double bias is also helpful. 

If you can't do any of that the primitive fix is a bolt through the gudgeon. But that is an awful solution.

No matter how many uni's you put on, this sideways load will take out a gudgeon. It is a tricky detail to get right...

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EXCELLENT!  I knew I put this post in the right place!

 

Short Term fix under way.  Full rebuild using the tips provided here is scheduled for my winter (5 months from now).

 

As interest, Ackermann is built in.  That little 10cm tab where the tiller crossbar mounts takes care of it.

 

Also, upon closer inspection this morning I found that the line that limits the travel of the rudders was broken.   I think the builder put it there to "keep it real" during a tight turn.  It limits travel to about 45 degrees.   This may have been the spark for the failure, though I realize that the cassette was somewhat under-built.  I replaced the line with a bit of Dyneema.

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Martin -

 

I did read that article and confirmed that there is Ackermann compensation built in.  By referring me to your excellent article, are you suggesting that it may be incorrect and perhaps caused this failure?

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sorry - I probably drifted that.  I didn't appreciate that you had some built in.  Was just suggesting that if you're doing a bunch of fixes that you might want to add that in to the mix as well.

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We also shortened our rudders.

Now that is interesting.  Did it affect weather helm?

 

Tell me about your thought process and the result.  I sailed in light air yesterday with the rudders halfway down and found it to be fine.  I am going to try in heavy air (when some comes in!)

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