BuiltWithNOF

 

STEERING SYSTEM

Steering Helm 1

Many years ago while sailing Magic Dragon (my old 41 foot, 30,000 pound, water pressing, unimaran ketch) the steering system failed.  The system on this mid-cockpit vessel was rather complex.  An Edison pedestal was located centrally in the mid-cockpit.  A chain drive connected the wheel to an idler shaft mounted to the underside of the cockpit floor.  A sprocket with chain connected to SS wire traveled into the bilge, turned there leading aft to more turning blocks under the aft cabin berth.  These turning blocks redirected the wire outboard through additional turning blocks that redirected the wire to the full circle bell crank mounted on the rudder post.  The final turning blocks were mounted on a plank that was tabbed to the hull at the bottom and one of the bunk support braces at the top.  The light fiberglass tabbing fractured, the support board pulled out and the steering failed.  Fortunately I was in open water at the time and could steer the boat using the emergency tiller.  What was the lesson learned?  Complexity is bad as it offers multiple points for possible failure.

TeleflexNFB_Box_usa-nfb42-2

A unique steering system was planned by Ocean Catamarans for their vessels.  Simple, off the shelf, reliable, inexpensive parts are used.  The off the shelf system uses Teleflex parts that are available world wide.  This is a simple coaxial push/pull outboard powerboat system designed for use with large outboard engines.  The system in the Dragon has worked flawlessly since it was installed.  A standard Teleflex dual cable big outboard engine powerboat system is used.  The dual system allows one cable to be lead to each stern and individually connected to each rudder.  As Millennium Dragon has balanced rudders the system uses only a  fraction of the force available to steer the boat.  No cross hull tiller connecting beam is needed.  The Dragon uses the NFB (No Feed Back) system.  This system is used with large outboards so that in a turn the force of the engines will not overpower the helm.  Clutches prevent the steering wheel from being moved when force is applied to the engines/rudders.  This is good as the helm stays where it is set for example when coming about.  This frees both hands to manage the jib sheets and/or traveler controls.  The down side is that any autopilot installed must be a wheel driven model.  Applying force to the tillers (rudders) will not move the No Feed Back system as this is prevented by the clutches in the hub.  Teleflex offers a similar package without the NFB feature.  This system should be used if a hydraulic, tiller mounted autopilot is specified.

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Single cable Teleflex system illustrated - Dual system used on the Dragon

The July/August 2007 issue of “Multihulls” magazine (Volume 33, Number 4) has an ad on page 111 placed by Ocean Catamarans.  The company is now under new ownership.  If you are interested in a new large cruising catamaran you should consider having yours built by this company.

In this same issue of Multihulls a two part article (“The Cat in a Potato Patch”) by Tyrone Currie and his brother, Sackville, describe the building of their Kelsall catamaran.  In “Part B II” on pages 100 & 101 Sackville describes his decision to install the Teleflex system.  I was one of the Ocean Catamaran owners he called for information and advised him to use the system without feed back if he was fitting a tiller/rudder attached hydraulic autopilot.  This is a very well written article that illustrates application of many well thought out sound principals of configuration and construction.  If you do not subscribe to “Multihulls” you may log onto their Web site and purchase a copy of this issue on line.  Note that Sackville and his brother elected to build a “squared off” settee rather than an “oval” configuration seen on some production cats.  This decision is not made just to simplify building.  The squared off settee/dinette provides much greater support while you are resting below sailing in a seaway.     

Steering_Stbd_1

I put a great deal of effort and time into designing the rudder/tiller offsets providing full size templets to the builder.  I got the “Ackerman” geometry right.  The Dragon will complete a tack from broad reach to broad reach.  Tacking while hard on the wind never produces a stall.  The key was to estimate the turning radius based on other large catamarans I have sailed.  Once this is established the individual turning radii of each hull (the rudders are approximately 20’ apart) is drawn and the angular deference between the rudders in a tight turn may be measured.  This came in between 7 and 8 degrees.  This means the tillers connected to the rudder shafts must be set at a “toe in” angle relative to the mounting position of the Teleflex cable ends of 7 to 8 degrees.  If you look at the tillers/connecting link for any beach cat you will note that the tillers are toed in at a slight angle.  As the boat is being steered, the inside hull/rudder is making a tighter turn than the outside hull/rudder.  Ackerman geometry compensates for this angular difference.  This allows both rudders to maximize equally their “bite” in the water and prevent one of them from stalling out.

During the build process, after the rudders and helm steering Teleflex Hub is installed, measurements are made from the Hub to each rudder/tiller location.  These measurements were in excess of 20 feet.  As the steering station is on the port side of the cockpit the distance to the starboard rudder was greater than to the port side.  These cables were ordered from Teleflex to match the measured distances.  Cable mounting is literally a snap.

During installation the rudders and wheel are centered.  The tillers are given their 7 to 8 degree rotation toward the middle of the boat (Counter Clockwise for Starboard, Clockwise for Port), the ball joint/adjustment is set so the business end of the cable lines up with the attachment hole (11” from center) in the tiller.      

Starboard stern locker with rudder/tiller and Teleflex cable connection.  Top view aft being up, forward down, port side right and starboard left.  Note steering cable enters on the port side.

Steering_Port_1

Port stern locker with rudder/tiller protective cover and Teleflex cable connection.  Top view aft being up, forward down, port side right and starboard left.  Note steering cable enters on the port side.

Steering_Port_5

Port stern locker with rudder/tiller protective cover over the tiller & Rudder Angle Indicator with Teleflex cable connection center.  Horizontal view into protective compartment with aft being left, forward right, port side ahead and starboard behind.  Note steering cable enters on the port side.

The photo to the left shows a look into the compartment behind the stove through the access port.  The Teleflex Dual NFB steering Hub box with two rudder cables attached is in the upper left corner of this photo.  The reservoir for the hydraulic sail control applications is just below and to the right for the steering Hub.  The Lewmar control/circuit breaker box for the #44 electric winch at the helm station is just to the right and above the hydraulic reservoir.

This is a standard, reliable, easy to install and maintain Teleflex NFB large outboard steering system.  Replacement cables and other parts are readily available but, as the cables are not as exposed as they usually are in an outboard application, replacement should not be necessary for a very long time. 

This is a No Feed Back system meaning that clutches in the hub prevent the wheel from being turned by pressure on the business end of the cables.  This means a wheel mounted Autopilot must be used.

Steering Hub

The photo to the right shows the wheel mounted Autohelm 4000 autopilot drive unit.  This is a belt driven system. Belts are available through a low cost provider of industrial drive belts at 1/4 the price offered by the original manufacture.  An  manual explaining replacement is in a file with other vessel documents.

The small electric motor that drives the belt inside the circular housing is seen to the right and just above the hub.  This motor is mounted in a short piece of PVC tubing that extends into the space between this cockpit bulkhead and the access panel behind the stove/oven.  The Autohelm control panel is above and to the right of this picture on the “dash board”.

The two switches to the right operate flood lights mounted ahead of the main crossbeam forward (for anchoring in clear water at night) and aft under the radar arch (for lighting the path to the dingy at night).

Steering Helm 2

What have I learned and would I do anything differently?  Not really.  This system has performed flawlessly for the past 7 years needing only one belt replacement (a year ago).  For near coastal cruising and island hopping through the Caribbean I would continue to use this system as it is.  If I were to follow Sackville Currie around the world or cross the Atlantic for a cruise of the Mediterranean, I would research Practical Sailor and the web to identify the best, most reliable hydraulic autopilot system on the market.  Then replace the NFB system with the one that would allow tiller connection of the drives.  This would be a piece of cake as the mounting holes and brackets would not change and if the cables needed replacement, the length could be measured directly from the existing units.  As it is about time for upgrading all the electronics to a fully integrated system a new autopilot might be considered but the existing Autohelm 4000 is probably adaptable through it’s standardized electronic connections.   

Mark Strube At Helm

Steering Helm 1

Steering Helm 2

Steering Helm 3

Steering Hub

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1

2

3

4

Steering Tiller/Rudder Stbd

Steering Assembly Cover Port

Steering Assembly Port

Steering Assembly Port

Port Rudder Profile

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Port Rudder Cross Section

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