Jon from Virginia asked a really good question: What happens if one of the rudders gets hit sideways by something or other? Which part of the linkage gives way?
Well, this is something that does happen. I once had a towing rode get looped around the rudder blade, and it snapped my autopilot in half. After a bit of head-scratching, I came up with the following arrangement:
The stick pointing toward you is one of the tillers, which will actually be made of 1.5" round stock, but I am showing it as 1" square stock so that the drawing is easier to make and understand. The tiller is interrupted by 3 hinged plates (the axes of the hinge pins are shown in red). Front and back plates are welded to the tiller, and the front part of the tiller flops back and forth freely on the hinges. To stop that from happening under normal conditions, the two sides of the tiller are held together using a spring (here shown as a pink rubber band, to make it easier to draw, and also to be funny).
Under normal conditions, the spring is tight enough so that the hinges do not open. But under extreme overload conditions, the spring stretches, and one of the two hinges opens up, allowing the tiller to bend. When the extreme overload is removed, the spring snaps the plates back together, and all is well again.
In the real set-up, the spring will be tensioned using a bolt, to make the action adjustable. I will probably make it extra-tight to start with, then make it looser as I sail until it becomes a bit too loose, then tighten it up some, and leave it that way.
Nice feature of this set-up are:
• that the rudder linkage will not only refuse to destroy itself when a rudder blade is hit from the side, but
• that it will still be trying to steer, as well as possible under the circumstances,
• that one rudder going out commission temporarily will not affect the ability to steer with the other rudder, and
• that it will snap back into shape spontaneously and go right back to work once the overload condition is past.
Lastly, there is the need to do "back-end alignment" to make sure that the two rudder blades are perfectly symmetrical and don't cause any extra drag. To do this, I intend to add a bolt and a jam nut that goes through the outer one of the three plates on one of the tillers and pushes against a divet drilled into the next plate, opening the hinge up a crack.
I feel much better about it now.
Well, this is something that does happen. I once had a towing rode get looped around the rudder blade, and it snapped my autopilot in half. After a bit of head-scratching, I came up with the following arrangement:
Under normal conditions, the spring is tight enough so that the hinges do not open. But under extreme overload conditions, the spring stretches, and one of the two hinges opens up, allowing the tiller to bend. When the extreme overload is removed, the spring snaps the plates back together, and all is well again.
In the real set-up, the spring will be tensioned using a bolt, to make the action adjustable. I will probably make it extra-tight to start with, then make it looser as I sail until it becomes a bit too loose, then tighten it up some, and leave it that way.
Nice feature of this set-up are:
• that the rudder linkage will not only refuse to destroy itself when a rudder blade is hit from the side, but
• that it will still be trying to steer, as well as possible under the circumstances,
• that one rudder going out commission temporarily will not affect the ability to steer with the other rudder, and
• that it will snap back into shape spontaneously and go right back to work once the overload condition is past.
Lastly, there is the need to do "back-end alignment" to make sure that the two rudder blades are perfectly symmetrical and don't cause any extra drag. To do this, I intend to add a bolt and a jam nut that goes through the outer one of the three plates on one of the tillers and pushes against a divet drilled into the next plate, opening the hinge up a crack.
I feel much better about it now.
You've essentially go yourself a mechanical circuit breaker! Neat.
ReplyDeleteThere might be other mechanisms that do similar things, or something that can be purchased off the shelf. The only thing that worries me is how well the alignment might hold under load, and if there are any small deflections that will misalign the rudder under heavy loads, without the mechanism kicking in.