Just been watching some of the 18' skiff footage on http://www.sailcam.tv/video_flash.php?vid=188 and it's left me wondering why we don't use bigger kite cats?

In the half-boat world, mast-top kites are common place, but seemingly not for cats. Obviously you'd have to come up with a way of keeping the mast in one piece, but the monos seem to manage it.

My first response is that the kite on the F18s/F16s I've sailed is quite big enough, thank you. But wouldn't a bigger sail just allow you to go deeper at the same speed?

Paul

Extra Drag....

Monos are not that efficient and rely on brute force to get them up to speed, where as cats are more refined and rely on lower drag rigs.

Some of the big ARC cats do have masthead kites but also have baby stays that run from the mast tip to the ends of the rear beam. If you remember back to the early days of catamaran spinnakers, they were big and full and have been evolving rather quickly into the flat and smaller shapes that we have now. I wouldn't be opposed to seeing some sort of masthead rig come out for development, but I think we might find that our existing setup is pretty optimized.

I believe the answer will lie in the same reason we don't run masthead genoa's upwind (except for a few who do so in very light conditions).

I'm guessing it has to do with apparent wind direction? Allthough the 18' skiffs are very fast, I don't know what their angles are. I know that even when we go downwind fast on a Cat, our apparent wind is well forward in a good blow, not light air. Rick has made the case for hooters instead of spins for cats and the Volvo 40's are also using hooters instead of spins. I don't know why we don't see those on the 18' skiffs though.

The wide platform of a cat allows for an open "slot" between the genneher and the mainsail. This accelerates the wind over the back of the mainsail and creates more lift. A mono simply is not wide enough to properly lead a headsail in order to achieve this effect.

Some cats even have articulating spin poles that optimise this effect.

Also, I have a masthead spin for my stiletto 23. It is total overkill and does not work s well as a flat modern asym. The VX40 guys have it nailed I think.

You mean a hooter-type, roller-furling headsail?

18' skiff is wider than your average cat, if I remember right. Not sure whether they're allowed to sheet to the racks, though.

Paul

I think they're not too different from asymmetric cats. Certainly the apparent wind is going to be well forward at those speeds.



What's the different between a hooter and an asymmetric spin? Is a hooter just flatter, or is there more to it than that?

Paul

If this was true, certainly they would come up with poles to move their sheeting points further out (like a jib pole on a monoslug). In my opinion, I think it's more relative to the balance point between available righting moment, overall weight, and sail area to make the best VMG downwind. Cats have a lot of righting moment and can handle hot angles downwind. As such, our sails are optimized for these hot angles. Skiffs have a little less righting leverage so they run fuller bigger kites.

I think Jake has it covered. In addition, our platforms are easier to control than an 18foot skiff (at least it looks that way from the videos I have seen).
Besides, haven't we agreed that tornados are faster than the 18footers <img src="http://www.catsailor.com/forums/images/graemlins/wink.gif" alt="" />

yes !

Not true, it's been shown that head sails actually do NOT increase the WS in the slot, they actually decrease it. What they do however, is keep the flow attached to the lee side of the main longer/more consistently which improves it's efficiency and therefore it's performance.

Interesting, would it be fair to say that the wider the "slot", the less it slows down the WS while still keeping the flow attached to the lee of the main?