I think this choice between boom-sheeted rotation limiter and trampoline-sheeted rotation limiter comes down fully on wether you mostly sail with a spinnaker sail or not.

Personally I have the trampoline-sheeted system on my own boat (F16). I sail nearly always with a spinnaker, both 2-up and 1-up. I'm finding that mastrotation control on a spi boat is pretty much on or off. Before the racing starts you'll fine tune the optimal upwind rotation and lock it there in place. Several crew use a seperate cleat for this; to lock this setting into place. Then after rounding the upwind mark you fully free the rotation only to fully pull the rotation in to the preset optimal trim for upwind when rounding C-mark. During the spi leg you never touch the rotation control and during the upwind leg you hardly ever adjust it. And you do then nearly always you increase rotation in order to get more power. However my experience is that even a suboptimal trim upwind can be acceptable unless the leg is really long. The reaching legs are often short anyway and mostly you are busy preparing for the hoist anyway. We (I) as good as always keep our upwind rotation on these small legs. In light winds you can get away with keeping your upwind rotation trim when sailing with a spi. Mostly because the spi induced such a big skewing to the flow experienced by the spi. After all on a spi boat you never travel out more than 1 foot from the centre of the rear beam. This means that the angle between the boom and mast stays pretty much the same anyway even when using a rotation limiter that is sheeted relative to the trampoline.

With the above explained usage, it is far cheaper to sheet the rotation of the trampoline and it allows a very simple setup that can be adjusted from the trapeze. An extra advantage is that you don't have a rotation limiter poking your eyes out when you are near the mast hoisting or doucing the spi. I also clears up the boom and generally looks tidier.

On my Taipan I have an extra advantage with respect to the trampoline bases rotation limiter in comparison to the boom-sheeted version. As explained in my other post, the superwing wingmast is more flexible in the sideways plane. This means that at a certain combination of rotation angle and leech tension angle the top of my mast will fall away to lee taking the whole head of my mainsail with it. The effect is that the top of the rig is quickly and fully depowered. I'm partly using this behaviour to control my boats heeling during gusts and while under spinnaker. I can influence the magnitude of this behaviour by adjusting my mast rotation control. It works like this. Under spinnaker in trying conditions, many wind with big wind speed fluctuation, I let out my mast rotation but not all the way as I would in really strong winds. I lock my rotation in place in such a position that when I sheet my maintraveller near to the centre of the rearbeam the rig is fully powered up with exactly the right amount of draft and twist in my mainsail. My mast rake it set up so that in this trim the boat is well balanced, with only a slight leehelm. I then head up to get the boat fully powered up and my crew works continiously to keep the spi always at maximum drive. When a large gusts hits us my crew keeps the spi drive at maximum while I do two actions simultaniously. I mildly steer down and I let out my main traveller. Both proportionally to the magnitude of the gust. The effect is that by letting the traveller out I

-1- reduce the angle of attack of my mainsail
-2- reduce the draft of my mainsail as my mast stays in the same position with boom moving more in line with this mast.
-3- the leech tension is moved relatively to the sideways plane of my mast resulting in the top falling away to lee depowering the top of my mainsail and increasing the twist profile of my leech in addition to the first initial and automatic response of my squaretop.

The net result is that I increase lee helm on my boat which really helps bear the boat down. I need noticeably less rudder angle (= less drag) to quickly turn the boat. It's prevent the boat from heeling, the bows are pressed down less and the boat seems to accellerate rather then heel. Also we have to bear down less, meaning that when the gust falls away we can maintain maximum power by pulling in the main traveller, bring back in the masttop and squaretop and increase draft, while only having the gentle head up a small amount to get back at the new optimal course which was the same as before the gust.

I found this mechanism to be so powerful and the Taipan mast to be rather resistant to failing under a spinnaker that I also use this trick to keep flying the spi on the last leg to the finish line. By letting out the main traveller I can often maintain a slightly higher course then the other spinnaker boats without slowing down or heeling to much. That is in relatively strong winds. In light winds everybody can do it as heeling is not a problem then.

This whole behaviour is not really important on a spinnakerless boat. Here your mainsail trim is alot more sensitive, their is no jib or spinnaker to just force flow over the mainsail even if the trim is slightly off. So in the case of A-cats and sorts I feel that a boom-sheeted rotation control is advantagious. Also because you guys let out a lot more main traveller then the spi boats do. Circular traveller tracks on a spi boat are just a dumb idea. You really don't need it as you never travel out more than 1 foot anyway. That is in a permanent way, you do of course temporarily to depower the rig in a gust but a circular track (maintaining draft and angle of attack) will then do the opposite of what you want.

Actually the addition of the spinnaker has allowed designers to simplify certain aspects on the boats. Mast rotation and traveller tracks are one of those things. The selftacking jib system is also alot more attractive on spi boats as the jib hardly needs to be travelled out when flying a spi. When push comes to shoove, you can even maintain your complete upwind trim of both the mainsail and jib on the downwind legs under spinnaker and not loose much ground at all. In crowded fleets this is a huge benefit. But I'm getting of track.

Main point is that on a spi boat I prefer the simple, out of the way, cheap trampoline-sheeted rotation control. On a spi-less boat the rotation control sheeted of the boom is advanagious.

Wouter