NE Dory Tiller Arm

In about 15 mph winds and nasty chop, the tiller arm broke at the rudder head. It snapped at the joint where the arm is notched to mount onto the rudder head. The filets held as the break has torn away a few plies of the rudder. I'm not convinced this is design flaw, although the linkage to the tiller stick at the end of the tiller arm was made with quarter inch yacht braid, pulled pretty tight, and I've read elsewhere that some are using shock cord, I find it hard to believe that the line was so tight as to cause the arm to twist as it is pulled skyward for a starboard tack. The chop was stalling my tacks and I may have pulled hard enough to cause the break. I was two and half miles out and am still recovering from the row across the wind.

Just 'cause I'm the nervous type, I'll construct repairs with solid mahogany and enough material to through bolt aound the rudder head, unless there are others with similar experiences and better solutions. I've been sailing my Dory for over a year on the lake near my home and have never had a problem. In fact, after years of sailing much larger and heavier craft, I find this design quite extraordinary.

larry


4 replies:

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RE: NE Dory Tiller Arm

Larry,

Glad you made it back OK.

A few thoughts on your proposed modifications:

1. Metal fasteners are stress concentrators. I'd avoid them entirely and stick with a bonded solution.

2. Plywood is more stable than solid wood, and stronger, too, because of the crossed plies.

3. Beefing up the arm by itself may not be enough. It could just move the failure to the rudder head next time. I don't own a Dory, but looking at the plans for its kick-up rudder I'm struck by that tab of single thickness plywood sticking up from between the cheeks. I'd be worried that making the arm heavier would cause the tab to go instead the next time.

If it was my boat, I'd make the arm thicker, make the area around the tab larger so there was more wood in front and back of the tab and continue the cheeks all the way up over the tabs to avoid the stress concentratoe caused by the transition from a greater thickness to a lesser.

Finally, are your pintles and gugeons properly aligned so that there's no binding when you move the rudder? A slight binding that is mostly unnoticeable when things are moving slowly could extert a sudden sharp stress when the rudder swings quickly. If there is a bind, getting rid of that may removethe need for further modifications.

Good luck,

Laszlo

   

RE: NE Dory Tiller Arm

Thanks Laszlo for such a careful response. I've adjusted my repair plan per your notes. Looking at the break more carefully, I'm convinced the arm's connection to the rudder head was the problem and perhaps a weakness in the construction of that joint. I agree that the rudderhead should be beefed up and in my case is necessary because of the damage to its side faces a consequence of the break. It seems clear now, that the break occured as a result of the downward force on the arm and the 12 millimeters of material at that joint just wasn't enough, coupled with a lousy glue job. Thanks for making me double check for binding and happily, there is none. I'm going with a sandwich of 2 pieces of 9 millimeter ply, same as the rudder and making sure the filets run out at least a quarter inch.

Again thanks,   larry

 

RE: NE Dory Tiller Arm

   Larry, any chance of a picture so we can see the failure and check our boats for signs of potential weakness?  Barry

 

RE: NE Dory Tiller Arm

Larry,

You likely are well into your repair, but I thought I'd pass along some pictures of how I made my tiller removeable using the drop out piece from the transom.  Now that I hear about your situaition, I guess what I did accidentally made it stronger, but that was not the intent at the time, just the removeable aspect was my only goal.

https://picasaweb.google.com/lh/photo/ZYUmRIhzwYwNwuLnHwypUTFolq1y-t7pqfyiNmzJPv8?feat=directlink

Then click the right arrow to see more pics

Curt   

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