The Effects of Gearing Speed.
Since last writing lots of testing has been done and a better understanding of exactly what gearing speed effects is emerging. The general understanding is that slow gearing is fast due to minimal flap movement but control is compromised, and fast gearing is slow but you gain more control.
With the cam you can target specific areas in lift delivery, lift control from lowriding to levelling off to ride height is pretty sorted so I concentrated on the ride height zone gearing through to off and made it 1mm per 10degs of wand movement, the speed of 1, all the way to off. In early testing I felt this was pretty good and even got the impression that lift was stronger with low gearing speed due to less variation, but this is not so.
Slow gearing makes the setting of your overall lift and AOA much more critical due to less control movement, rudder trim inputs become more frequent so your head is in the boat more trying to stay in the groove and height to windward is harder to maintain so you end up off the pace overall. The boat was silky smooth through the water and speed was ok, I felt in control enough but struggled with good height to windward. I have fitted the boat out with some of the best known foils as a constant to test with too so knew what I was looking for was going to come from somewhere else.
I started to make some enquiries with various fast mates using standard systems to try and get an idea of what their gearing was at ride height, - short answer was they had no idea and generally weren’t that interested in working out what it was, it felt right so they were happy, which is fair enough. So I had to get an idea of what their gearing was by observation of their boats and comments about how much wand travel they had at times of successful gearing speed. What I found was that their slow gearing was much faster at ride height than what I was using with the cam. The cams ability to deliver strong early lift/gearing then back off gearing made this possible, if the gearing was that slow right through the range you’d never get high enough or have enough control.
For example the Mach 2 bowsprit delivers a speed of approx. 5mm per 10degs of wand rotation atride height and an overall movement of approx. 30mm, hence the reason to gear down at the bellcrank, the flap can’t take much more than 14mm overall movement. Looking at where they generally have the bellcrank set they would be using gearing in the range of 2-3mm per 10degs of wand rotation. So the cam I was using was the C6 with the ride height speed of 1 and its overall flap movement was down to 10.5mm, I had also made the C6.2 with a turn off notch at the end to flick the flap off an extra 2mm and a C6.4 with 4mm extra. First I took the C6.2 and altered the curve through ride height to off to be an even speed, the extra 2mm off through this movement increased the ride height speed to 1.5 with an overall movement of 12.5mm.
I then went sailing and immediately the boat was easier to keep in the groove upwind, particularly in gusty conditions, and upwind performance improved. Gybing the boat flying high was safer too. The boat was still feeling pretty smooth with that gearing, this cam was now the C7.
With that improvement I then went the next step and re-profiled the C6.4 cam in a similar way down to its turnoff position, this gave a constant ride height speed of 2 and an overall movement of 14mm, this is now the C8 cam. Back on the water the improvement again was evident, most importantly height to windward improved dramatically.
Yes the boat now rides much bumpier (mind you I had become used to the gearing of 1) but the effect is that the boat has more lift with control. Speed comes from being able to fly high more constantly reducing the drag from verticals and overall lift and so height to windward is better due to the flap turning on more in response to the boat dropping.
So I am happy at this stage with the C8 cam for use with foils that have a flap area to mainfoil of 37-40% (most foils at the moment). The basic makeup of 14mm of overall movement, ride heightgearing of 2 that speeds up to 3.3 below ride height to get you onto full lift earlier feels about right. I have made a C9 cam with 1.5mm more overall movement for foils with smaller flaps like the Macita.
It’s a bit ironic that foils that have smaller flaps to be fast then have less control and then need more flap movement, but there you go. It is most likely that you could gear down more at ride height if theflap area increases in foil design, time will tell, but the C6 & C7 cams are there waiting.