My day started early, 2.30 am to be precise, EST. Our Owner Rep, Akan, from his home is Marmaris Turkey, began by asking questions about the steering system.
He is working through details of the engine room installation. Steering was now top of that list. Essentially, trying to understand thinking behind the system he's inherited and that predated his engagement.
So, without pretending to be an expert on the subject, this is how it works.
Wills Ridley - the importance of accurate steering. on the Corinth Canal, Greece.
A yacht is pretty useless without steering, so we focussed on reliability. Following on from that was functionality.
We wanted full Dynamic Positioning with dictated independent rudder operation as we have no stern thruster.
It is potentially a complicated installation, so thorough commissioning was essential, and we wanted good local representation.
Any system we installed would have to work within these three governing considerations.
Firstly the steering gear itself, being the actuators and their controls. We looked at Kobelt and Wills Ridley. Both are well-respected suppliers of steering systems for commercial and military applications.
We settled on Wills Ridley as we knew the local representative (Navantec) and trusted their input. The system supplied uses a dedicated pump, hydraulic system, actuator and huge cast alloy tiller head for each rudder. Pumps are provided with single phase 1.5kW power. Separate pumps and tanks are mounted on the same platform. Pumps may be run independently or in duty/standby configuration with auto switchover in event of failure with the duty pump. Rams are double acting and a single rudder can be disabled by hydraulically locking it. As designed, we achieve a >70-degree swing and a relatively rapid 10-second swing time, stop to stop. Emergency steering is also available directly from the control system in the engine room and acts on both rudders. Two jog buttons, a "left a bit, right a bit" sort of arrangement.
Rudder control allows for duplex, simplex or Praxis Dynamic Positioning systems. Hydraulics are fully redundant and fast acting.
Speed and force of operation are perhaps worth further discussion. Having spoken to quite a few old salts and Artnautica about it, we found Wills Ridley summed up the problem nicely. In a following steep sea, water on the rudder can act as if the vessel is in high-speed reverse, a.k.a; it flows in reverse across the rudder as the wave passes under the stern of the hull. The stern rises, the bow digs in, slows and "anchors" in the seaway.
At this point, there is a tendency for the stern to swing out pushing the hull towards a broach. A fast-acting powerful rudder and reserve power will help keep you out of trouble. Steve Dashew's site also references this with some illustrative video studies taken on his FPB designs.
We have two helm stations plus a docking station. Control from the helm uses commercial-grade marine Type Approved equipment from Praxis Automation. The helm has, FFU (Full Follow-Up *) and NFU (None Follow-Up *), autopilot / heading control*, and a Dynamic Positioning Joystick* function. We can trim, set toe in or out, set response speed and otherwise optimize steering functions. The rudders operate independently. The control system uses a duplicated, high bandwidth ethernet. For a further discussion of Vanguard's DP system, look HERE.
Praxis rudder control system with two helm and one docking station.
We have the physical end of the steering system wholly duplicated. We also have the control system duplicated and can operate either rudder independently at a push. At one meeting I did mention a backup hydraulic station at the helm but met with derision. Praxis was right; their system is Type Approved for the application and inherently more reliable than the backup we considered, times two independent systems. I still may fit one though!
Read also: Visiting Praxis Automation - Part 1
There are many ways to configure a steering system, and I would not claim that ours is better or worse than any other. This is not a new technology but it does present good and poor examples as documented in the various Marine accident reports. It is fully redundant, powerful and fast acting which is reassuring given our likely destinations. These features however, come at a cost in $$$ and complication. Time and tempest will be our dispassionate judge.
Lucky for me, my wife, Sebrina, is very understanding, generally so if I delay asking until after the second glass of evening wine. :-)
Okan Kuzu - Navantech
Chris Leigh-Jones
* FFU steering - the controller moves the rudder to the angle set. (like a wheel)
* NFU steering - the controller continually moves the rudder whilst the level is activated, a jog lever.
* Joystick - the controller produces fore or aft plus port or starboard motion on the vessel or any combination thereof. This is also provides the NFU steering function.
* Autopilot - the heading controller navigates a given heading or course made good, it is also augmented to provide dynamic Positioning functions.