The ultimate limits of windvane steering

When there is no wind there can be no steering signal, but a sensitive windvane system will start to function as soon as there is enough wind to fill the sails and set the boat moving.

A servo-pendulum gear needs about 2 knots of speed through the water before the water flowing past the hull can generate the force required in the pendulum rudder blade and steering lines to turn the main rudder. Unfortunately this all presupposes a calm sea. If the sails are collapsed by left-over swells, the boat will lose its drive and the windvane system will have nothing left to offer. The only remedy here is an autopilot.

ULDB Budapest just after launching Slovenia, June 1996

Stronger winds generate a stronger steering impulse from the windvane and improved boat speed increases the force available from the pendulum rudder. If the boat is perfectly trimmed, i.e. the steering force required is low, the pendulum rudder will swing out just a small distance and exert only moderate force on the main rudder. Not until the boat requires greater rudder pressure does the system bring its full reserves of power into play. To meet the need for more force the pendulum rudder swings out further from centreline, thereby increasing its leverage and generating considerably more steering force. This illustrates how proper and effective damping gives servo-pendulum gears such an advantage in terms of range of conditions and power reserves: steering quality generally increases as wind strength and boat speed increase.

This trend holds until breaking seas make manual steering compulsory. A windvane steering system cannot see breaking waves and just carries on steering right through them, a potentially dangerous habit for both vessel and crew. Blind South African Sailor, Geoffrey Hilton Barber who crossed the Indian Ocean from Durban to Freemantle in seven weeks in 1997, even trusted his Windpilot Pacific in a 65 knot gale under bare poles.

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Wind strength

Fig 5.21 This figure uses the same formula as Fig 5.14 but here it is boat speed rather than torque which is plotted against strength.

The pendulum rudder rotation angle assumed here, 6°, is intentionally on the high side in order to illustrate the tensile forces theoretically possible. Rotation angles of 0-3° are more realistic as the tensile forces required at the main rudder of a properly trimmed boat are very much lower. In principle, the poorer the trim, the higher the tensile forces that will be required at the main rudder; thus the greater the rotation angle needed at the pendulum rudder before the feedback from the windvane signals a return to the desired course and the pendulum rudder/ pendulum arm is restored to centre. This automatically entails a larger yawing angle. The faster the system reacts, the smoother the course will be. For boats whose maximum speed is limited by design as a function of length along the waterline, the curve plotted in a figure ands when the boat reaches hull speed. For boats whose maximum speed is much higher or even unlimited (ULDBs, catamarans), the curve continues appropriately. A windvane steering system has to give up going to weather if the acceleration of the boat when accidentally bearing away (rudder or swells) is so great that it pushes the apparent wind angle forward to the point where the windvane can no longer tell what is happening; the apparent wind angle on the faster and lower course. What generally happens is that the boat falls some way off wind, accelerating sharply, and the windvane detects no difference and institutes no corrective rudder movement (see The ultimate limits of windvane steering systems).

Remember: Windvane steering systems cannot be trusted to manage planning boats, since the principles outlined above preclude a reliable steering impulse. The danger of a crash-gybe is ever-present once the windvane becomes confused; only the most irresponsible skipper would risk losing the mast just to save some time at the helm.

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How To Have A Perfect Boating Experience

How To Have A Perfect Boating Experience

Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.

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