Equipment | Autopilot(s)
Even a well-rested crew cannot reasonably be expected to helm the boat for more than two four-hour shifts a day. That means it takes three crew to continuously helm a boat like Jocara. In our minds, then, a good autopilot is worth three crew, plus it never gets tired or falls asleep at the wheel and doesn't need a place to sleep or be fed!
As with all critical items on board, there must be backups. In the past, we've had an electronic autopilot and a purely mechanical backup - which makes sense since it could replace the electronic autopilot in the event of autopilot failure or electrical power failure. Jocara, however, is a heavy boat and, particularly for downwind sailing, difficult to manage with a mechnical system. Besides, we have enough stuff cluttering the stern already (see the davits section)!
We therefore have two (almost identical) electronic autopilots on board, made by Cetrek in the UK. They each consist of a central computing unit with an electronic fluxgate compass and rudder position indicator as input devices and a hydraulic pump that drives the steering rams as output. The system human interface is through a control head in the cockpit.
The computer senses the direction of the boat and commands the rudder pump to produce corrective rudder movements, sensing the response of the rudder and the induced yaw of the vessel as feedback to tune its responses. Because it knows how much rudder has actually been applied, and the boats response, in addition to the 'noise' in the ship's heading caused by the waves, the unit can assess the sea state and adapt its control accordingly. As a result, when it works, it generally does a better job than a human helmsman!
We have two independent systems, the only difference between them being the control head, one of which is a portable hand-held unit on a coiled line, the other fixed in the instrument bulkhead. Their functionality is identical.
We've had trouble with them losing calibration, and with the HF radio scrambling the communications to the control head while they are operating, so that they switch off or become confused during radio transmissions. We also find that the generator, placed in the same compartment as the computers and compasses, understandably affects the compasses when operating.
© JIOQ 2004, 2005