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Sunday, October 27, 2013

Steering Main Gear Final Design

So, this weekend will not see the final steering "in" just yet. Probably next weekend as I have a couple more things to machine. In the meantime, here is a drawing of the "final" design as everything has now been fitted.

Side view of aft steering gear.

Item descriptions starting lower-left and moving clockwise:

Self-Aligning Roller Bearing

A bearing with small rollers fitted onto the 60mm rudder post. Rollers are in a delrin "ball" socketed in an aluminum housing. The roller bearings bear the sideways forces on the rudder on the "upper" side of things. The aluminum bearing housing is held captive in a specially machined section of G-10 tube, which is glassed to the hull with multipler layers of glass and epoxy. The ball & socket design of the bearing allow things to continually align themselves, as the rudder turns, for any slight sideways movement of the rudder post about its axis.

Neoprene Gaiter

This is the rudder post "shaft seal" Made from neoprene sponge fabric (like found in wetsuits), it is hose clamped around the bearing housing and the rudder post. The stretch quality of the neoprene and extra gusseting allows the gaiter to move and stretch as the rudder moves. The rudder port will be a few inches above the waterline so things should be dry most of the time. The gaiter will keep the ocean out as the boat pitches in waves.

Rudder Post Tiller Arm

This is the arm responsible for moving the rudder via the drag link. Heavy duty aluminum clamped to the rudder post and aligned with two set screws.

Upper UHMW Stopper Bearing

This is a bearing designed to slide on the rudder post tiller arm collar. It does not normally bear much force, but is there to prevent vertical movement of the rudder within the other bearings. Perhaps in a case of the rudder going aground (hopefully never).

Drag Link

An adjustable linkage that transmits movement from the reduction gear output arm to the rudder post tiller arm.

Reduction Gear Output Arm

The angular movement output from the main reduction gear.

Main Reduction Gear

This is a big heavy piece of machined aluminum mechanical bits responsible for converting rotational movement from the cockpit pedestal wheel, into angular movement to turn the rudder. The gearing is a 7 to 1 reduction, meaning that seven complete revolutions of the wheel, will turn the reduction gear output arm one complete revolution. This means a typical 72 degree sweep of the rudder "lock-to-lock" will require about 1.5 revolutions of the cockpit wheel. This seems a little low for the moment. A more typical steering input seems about 3 revolutions of the wheel. We can later add a 2:1 gear reduction into the system when things are fine tuned.

Autopilot Drive Input

A secondary input shaft in the main reduction gear allows for the addition of DC motor for an electronic autopilot.

Transmission Drive Input

This receives the inputs from the torque tubes leading from the cockpit pedestal and wheel.

And that is basically it. Most of the parts are made by Jefa of Denmark and supplied by the fine folks at PYI inc in Washington State.

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