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Friday, December 19, 2008

More on Steering... still

So, if you have been reading this blog, you have heard me go back and forth what type of steering to install. I have been split between cable-in-conduit and transmission steering. It was looking like cable-in-conduit was going to win out, not so much because it was cheaper, but there was the "18 degree problem" with the transmission steering. The 18 Degree Problem Just a recap on what this is. The Westsail 42's rudder is raked back at 18 degrees. With transmission steering, to be efficient and reduce stress and wear on parts, you want the input and output angle on the universal joints to be very close if not equal. Now, as one follows the geometry from the steering pedestal to the rudder post, *something* along the way must take up this 18 degree difference. While one could adjust each little bevel box on the way a couple degrees, it is not enough to take up the entire 18 degrees. Cramped Spaces There had also been the problem of cramped spaces in which to run the transmission steering. Existing spaces and bulkhead placement really confined steering component placement and limited options. Aft Berth and A Solution I had stated earlier that I wanted to get the steering design hammered out, and dry fitted, before roughing in the aft cabin. Well, upon closer examination, I determined that doing the rough frame-in would be ok and would still leave plenty of room to workout the steering. Once I did this (couple months ago) the key to the solution of these two problems revealed itself. The primary restriction for the transmission steering design so far was that the torque tubes needed to run under the floorboards, all the way aft, where things really narrow. But, once the framing for the aft berth was installed, I noticed there was significant overhang over the aft most floorboard (it didn't surprise me, as this was the design all along). So I thought "why not route the tube to come up through the floor and under the berth and then right angle aft?" This would solve the cramped space problem and, since the tube is under the berth it cannot be seen nor get in the way of anything else in the cabin. So with that I did another iteration over transmission steering. During which I noticed that Jefa makes a beveled final reduction gear that I could turn sideways and rotate the output tiller arm to take up the 18 degrees. This introduces a 2 degree deflection in the final drag link, which is acceptable. Did you get all that? Well, if you didn't here is a drawing.
From Building A Westsail42:Drawings

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