indeed, but only the A-cat and Formula 16 class rules allow this type of adjustment while racing. As far as I'm aware ALL other catamaran classes forbid this kind of adjustment in their class rules. Certainly the F18, F20 and all one-design classes do so.

I seem to remember that a few A-cats even have linked up their downhaul and diamond wire tension systems so that pulling on the downhaul also adds some tensions to the diamond wires.

I must say however that this system hasn't caught on in the F16 class yet and not too many A-cats seem to be using it either although more so than in the past. I know the boats coming through Peter Saarbergs shop tend to have this system but not many others. At least that was the impression I got when I last checked up on it.

I'm not really sure how good this adjustment is in real life sailing. A guy at my club uses it and he is indeed a very good and fast sailor. He is always scoring a place in the top 3 of our races, he sails an open 15 sq. boat = a rather heavily modified A-cat (wider, more sail area, fully angled boards etc). But he seems to adjust it mostly on the beach dependening on the conditions and only during sailing in large waves where he wants some extra power to punch through. I seem to remember he tightens them while sailing with the waves (flattening the middle of the sail) and loosens them when sailing dead against the large waves. In other conditions I don't think he adjust the system at all. Of course the first (on the beach adjustment) can also be done (and ist done by serious crews) using the turnbuckle adjusters. The adjustment on the waters seems to be pretty rare. In my personal experience the potential to make the wrong adjustment is rather significant so some form of calibrated scale is needed. Meaning that if you don't return to the right amount of tension (high) for the upwind leg can really kill your pointing ability (to flat middle section) or make the boat slow (to full in the middle. Or even a combination of both.

The biggest advantage of the system is however that it allows you to play with it during training and thus learn heaps on the right mast tuning (prebend). This is alot more practical then setting some prebend and spreader rake, go out sailing and then go back to shore, adjust the turnbuckles and do a test sail again. havin said this I know teams that bring a spanner with them while training and adjust the diamond on the water as well till they have the setting they want.

With regard to F16's I don't know wether this system will catch on as it is again another line on board that needs to be lead away with some bungee system and the spinnaker negates pretty much all fine-tuning for downwind legs. This allows you to setup the boat fully for upwind work and just have the spin drag you downwind not wasting time in adjusting the settings. F18 and others (if it were allowed by their class rules) would probably show a similar trend.

A-cats of course don't have this (major) chance of sailing setup and here fine-tuning of the mainsail for downwind sailing has the potential to really pay off.

And that is what I know about this system as of yet.

Wouter