Should a C250 owner with the pull / pull system consider an open wire conversion?

During 2000, Catalina and Edson combined efforts to cure problems of the wheel equipped 250.  Catalina redesigned to a balanced rudder to reduce torque loads and Edson abandoned the single push/pull cable and went to a pull/pull design to cure failure issues associated with the push/pull design.  Reports of failures to the new design have been offered to the National Association forum.  Those have outlined a bent cable mounting bracket that caused excess play and the jumping of the chain on the steering sprocket, and the other was excess play allowed the chain to jump links while sailing in windy conditions.

A recent report is more serious, outlining a near catastrophy when one of the eye bolts broke suddenly and left the boat without helm.  Edson replaced the eye bolts,  but after a current inspection, the new bolts were also found to be deformed.  The owner converted to open cables.

In the pull/pull design,  Edson solved the failure problems of the push/pull design but fell short of reaching an optimal system.  The new design still uses flexible cables which are prone to drag.  It employs a design that actually requires some amount of play and it didn't resolve the limited steering ratio between wheel and rudder.

Larger boats use open wire controlled steering between the wheel and a quadrant attached to the rudder stock.  A stern mounted blade rudder however doesn't  allow use of a quadrant in the traditional way and Edson chose a simply approach to rudder hookup that failed to provide arc compensation.  Without arc compensation, undesirable play is a system necessity.  Further, to keep the amount of play within reason, the steering ratio couldn't be improved.  The drawing below should illustrate why that is true.

In the drawing, if the rudder swings from position A to B, the length of the cable Z becomes X+Y (longer than Z).  This means that if the cables are tensioned for no play at rudder position A, then the cable will be too tight at position B thus the cables have to be adjusted for no slack at position B and will have deadband or play at position A. 

If the rudder arm were lengthened to increase steering leverage (position A moved forward several inches) to increase the lever,  the arc becomes greater as does the need for arc compensation.  Not to compensate would incur deadband so great the chain would jump teeth on the sprocket. 

The 250 uses about one half  turn of the wheel from center to rudder lock.  That ratio is unsatisfactory for ease of helm and preciseness of steering.  The ratio was determined probably by the 1st design, which had a limited amount of travel of the push / pull cable.  The second design though not limited by the pedestal mechanism, is limited as illustrated above because the design does not employ arc compensation.

Another shortcoming of the Edson design is that as the rudder is moved from center, a proportionately greater effort is needed as the rudder moves toward lock position.  This is undesirable because it means as the hydro forces on the rudder become greater, the effort of the wheel becomes less, losing around 30 percent of leverage.  The open wire conversion design is opposite, it proportionally increases the lever by about 50 percent,  when its needed.  This means a system that has 150% greater leverage at center position will have over 200% better leverage near rudder lock rather compared to a system that starts with much less and then loses 30%.  Sea trials of the difference tell the story much better than words can.

When I first offered the conversion, it was felt that a decision to upgrade from the pull/pull design would rest on how discriminating the desire for the best possible helm control. With the reports of failures, some are now converting because of failures.

The open wire conversion totally eliminates play because it employs a  compensating design that allows the cable tension to remain the same regardless of rudder position just as a quadrant would.  It uses ball bearing sheaves and thus eliminates the drag associated with sheathed flexible cables.  And, most important, it more than doubles the steering ratio and thus gains the necessary leverage for an easy helm.  An additional benefit is more precise steering in part because of the elimination of deadband and the greater ratio allows more precise control.   Last, if a wheelpilot is used, the more than doubled leverage makes it possible for the pilot to function in a wider range of conditions without becoming overloaded by weather helm.  

When I first offered the kit, my thoughts were that it would likely be only for those with the older push / pull design, but as I've listened to the comments of those with the newer pull /pull design, it's apparent that the new design has shortcomings that the open wire design can resolve.  I'm reminded that when I first commented about going open wire, I received mail from a gentlemen who in fact was unhappy with the play and drag of the new design and had replaced it with an open wire design which used arc compensation but didn't offer other design goals on my wish list such as
  • improved steering ratio
  • no loading of the rudder arm so that the rudder could be removed without messing with slakening and tightening the cable tension
  • minimum penetration into the aft berth (less than the Edson system)
  • ease of building and installation
With reports of bent brackets, failing eye bolts, remaining torque issues, excess play and chains jumping the sprocket it now seems that owners of both Edson systems using flexible cables can benefit from the open wire conversion for both safety and better helm control.