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Tuesday, March 12, 2013

Steering: Final Design

It has been a while since the last mention of the boat's steering system. Final framing under the aft cabin berth has been waiting on the final design/fitting of the below-decks steering mechanics. I have putting this project off as long as I could. We have been comparing designs using a traditional Edson pull-pull cable systems, and modern geared transmission systems, like that offered by Jefa Systems.

Elevation view

Plan View

Cable vs Transmission, Edson vs Jefa

After iterating over designs, we were ready to pull the trigger on an Edson cable/conduit system. But after one last look at the Jefa system, we changed our minds. Here is a summary of the major decision points:
  • Rudder Response: Jefa
  • Ease of installation: Jefa
  • Maintenance: Jefa
  • Mfgr Support: Jefa
  • Design and manufacture quality: Jefa
  • Space consumed below decks: Jefa
  • Cost: Edson

Rudder Response

Our little boat has tiller steering. This direct mechanism gives the best, quickest, force-feedback of loads on the rudder (transmission of forces from the rudder to the steerer). By feeling the loads on the rudder, at the wheel, you can better understand how much weatherhelm is present. This can be used to steer and balance/trim the sails to get most efficiency (speed). I have sailed boats with cable and hydraulic steering and found lack of (or delayed) force-feedback somewhat disconcerting. Hydraulic systems seem particularly bad for this, and cable systems can loosen due to stretch over time ("slop"). The geared, torque-tube systems will transmit rudder forces most directly and give the best accurate force-feedback. 

Installation

This is a center-cockpit sailboat. The steering mechanism will always be more complicated than an aft-cockpit configuration. An Edson cable system could be installed under the floor (as was in the factory), or down the port side through bulkheads (as was our planned cable/conduit system). Either way, as there are no large quadrants or idler pulleys, the Jefa system makes for an easier installation. It will be as easy as cutting some holes and bolting a couple components to bulkheads.

Maintenance

A common cause point of cable system failure is lack of lubrication. Cables can fray and eventually break if tension and lubrication is not kept in check. With transmission steering, there are no lubrication points. The bevel gears are in sealed housings, using sealed bearings. While the units can be disassembled and serviced, this should not be needed under normal circumstances. 

Support

The North American distributor of Jefa is PYI Inc in Mulkilteo, WA. Just an hours drive away from us. Edson is in New Bedford, MA. I met the folks at PYI and was able to see their operation. They know their product well. Not that Edson does not, but if I can drive just an hour with drawings in hand and talk to a technician face to face, well...

Quality

I have seen both Edson and Jefa components. I am quite impressed with Jefa. All components are machined, not cast, for strength and precision. Again, nothing necessarily wrong with Edson components, but some are still 20-30 year old designs (some might say that is "proven" (old?) technology I guess).

Space

The Jefa transmission system, as there are no large steering quadrants and idler pulleys, is more compact than a cable system. Space consumed under the aft berth and engine room will be minimal.

Cost

An Edson cable-in-conduit system IS cheaper. By about $2K-$3K. But due to items mentioned above, (especially force feedback, installation, quality) we think Jefa is worth the extra cost.


Main reduction gear (replaces traditional quadrant)

Bevel gear (transmits torque around a corner)

Parts have been ordered. Installation will start in a few weeks.
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