How to twist

Now you may be about to wonder how I never noticed this before, but anyway... I was looking at my rig on Saturday (on the shore) and pondering the setup and shape as I often do. I had the North P2 on and it looked ok but I wanted the top to twist a little when sailing upwind.

Some twist is generally desirable (in airplane wings as well as sails) - too little twist and the airflow across the sail can stall. Of course it is always a balance - too much twist reduces lift and increases weather helm. 

Anyway, I was fiddling with all the controls - the kicker, mainsheet, clew outhaul etc. Now I was always told you should use as little cunningham as possible upwind as it tends to flatten the sail and move the centre-of-effort forwards, which might impact how high you can point on a beat. And that is what I thought the function of the cunningham was: flatten the sail as the wind strength increases.

But when I put the cunningham on a bit, the top third of the sail immediately started to twist. I repeated this several times, putting on more cunningham, letting it off again. Even quite a small amount allowed the top of the sail to twist.

I was thinking I must be a bit dense not to have noticed this effect until now. As often happens at Frensham, it wasn't long before a really good sailor walks by - this time it was Mike Everitt who is one of the best Hansa sailors in the country. I showed him the top of the sail and the effect of the cunningham and we talked about it for a minute or two. I was relieved he didn't call me an idiot (perhaps he just thought it). He asked me if I had a bendy mast, but that's the interesting thing for me - I really don't. I have an old Selden Cumulus which is one the least bendy Solo masts you can get. The twist effect is completely independent of the mast type, though it is true that a lot of cunningham will bend the mast - but that's a topic for another day.

I didn't do anything abut this discovery yesterday, but today I adjusted the cunningham a bit before the start of our Solo club race, which is usually pretty competitive (9 boats out this time). You could definitely see the effect on the top of the sail, so I tried using a little cunningham on each beat, adjusting it to use as little as possible but still get a nice twist at the top. This worked well - I was quick upwind and even won the race (!) which is a bit of an over-achievement for me.

But I don't know how I missed this. I have been to several talks by the great Mike McNamara. Even my cat couldn't believe I didn't know the basics of sail adjustment. Just look at his face - now that is a bemused cat. 😼⛵