2352hrs 31 Jan 2005 SYD time 49’32”S 178’06”W Map Ref 39 1663nm
Windvane wizardry part 2.
To set it up, we trim he boat so that it would sail itself but for the motion of the waves and changes in wind strength. (Really easy to do in a boat as sea kindly as Berri and important to get it right – in the storm before we got bashed, I accidentally knocked the steering lines off the tiller and didn’t notice for half an hour or so, but the boat carried on in big seas, probably wandering a lot more and taking longer to return to the course she was trimmed for. How could I not notice? Slack, that’s all, and a seaworthy boat.)
Then we align the aerofoil with the apparent wind, connect the steering lines to the tiller and go below and talk to the man from Dublin. Nothing to it really. So, what happens? As the boat moves through the water, its direction is influenced by the waves and by wind changes. Changes in direction also change the apparent wind and the aerofoil is no longer perfectly aligned but feels the new wind on one side or the other and rocks away from it as it feels the new force. The aerofoil itself is not powerful enough to move the tiller but as it rocks, it causes the paddle to rotate about its vertical axis, so it in turn is no longer perfectly aligned in the boat’s wake and is moved sideways by the water flow. Water flow on about half a square metre of paddle exerts considerable force and this moves a big lever that is connected to the tiller by lines and pulleys and the tiller moves the rudder to bring the boat back on course. Happens much faster than I can write it and it is amazingly accurate when properly set up. Sensitivity to all wind strengths is achieved by using different sized aerofoils and by adjusting the counterweight that holds the aerofoil upright either up or down. Fully down makes it very stiff so requiring more wind to move it, fully up is very sensitive to tiny changes in wind strength. And one final bit of cleverness – the steering lines are connected to the tiller by hooking one link of a short length of chain over a stud on top of the tiller and the whole thing can be very finely trimmed by selecting the exact link needed to keep the boat on course. An elegant and ingenious piece of gear. The downside is that it follows changes in wind direction very accurately, always keeping the boat aligned to the apparent wind but not to the required compass course, so, for example, if we had set it up to miss the Antipodes Islands this morning and gone to sleep and the wind had changed…Very important to monitor what is happening all the time.
Does that cover it Kevin? The small adjustments we made in Dunedin seem to be working.