New A Class Catamaran Rig: Square Top Jib

Discussion in 'Multihulls' started by Doug Lord, Jan 17, 2011.

  1. CT249
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    CT249 Senior Member

    I'm not an expert on cat kites and I'm not sure about the current foiling As, but the last generations of pre-foiling As would have been faster with spinnakers a lot of the time. This was shown pretty spectacularly a few years back when the Formula 16 cats arrived. There's a pretty little 16' cat called the Mosquito which looks like a baby Tornado and was rated about 20% slower than the As, or about the same as a Hobie 16. When the Mosquitoes added a small spinnaker to become a baby F16, they could actually beat the world's best A Class cats downwind a lot of the time, despite having a much smaller mainsail.....they got quite a reaction from world A Class champs like Glen Ashby and Steve Brewin.

    There'a an interesting piece on the web that described how a fairly modern wing-masted C Class cat from the UK (their previous Little America's Cup challenger) fared in a regatta against spinnaker flying production cats like Tornadoes, M20, F18, Nacra 20c and F16s in about 2010.

    One race was in light winds; "about 4-5 knots". The C Class sailors reported "downwind we just got crucified by the kite boats... Our angles were terrible whilst the kite boats could still make a decent VMG....our race was effectively over half way along that down-wind leg.We would get left behind downwind... and find ourselves coming back into the top mark with the front runners."

    There was around 10-15 knots in the later races, and the C Class guys had some damage but reported "We had great starts on the third and fourth races and gave everyone a good look at how a wing-sailed catamaran can go to weather... even with only half a dagger-board. Towards the end of the third race I began to move further to leeward down-wind and trade speed for depth. It worked a lot better and when in the groove we could almost... but not quite hang on to the good guys. Whenever we lost it we would get rolled by anything with a kite including the Spitfires from time to time". Note that the Spitfire is a production boat just 16' long, and the C Class is an expensive custom 25'er.

    The British boat was not the world's fastest C, but the skipper reported "my gut feeling is that a good crew on the latest tweaked ‘C’ i.e. Fred and Magnus on Canaan... would come out on top" against the smaller cats with spinnakers.

    I was quite surprised to read the above, since C Class cats used to be much faster than anything else because of their amazing upwind speed. However, even in the '80s the 18 Foot Skiffs were faster downwind than the world's best C Class of the time in one special race where they came together, as (if I recall correctly) were Tornadoes which were experimenting with spinnakers.

    Even in really fast craft, sheer sail area can really make a difference. Whether the beachcat-sized foilers have moved into a different zone is an interesting question. Racing windsurfers have a top speed comparable to a beachcat size foiler and they tend to find that big sails work better downwind.

    One point is that the drag increase may be a lot less than you are assuming -the spinnaker on the fast cats is very flat, more like a headsail than a typical skiff-style assymetric. Secondly, you don't actually get any more speed a lot of the time - what you get is the ability to head lower at the same speed, and perhaps (in light winds) the ability to generate more apparent wind at the same angles. Thirdly (and I know this seems to be at odds with the info above) the overall speed improvement you get from adding a spinnaker is generally only about 2% if I recall correctly, partly because the spinnaker chute adds a lot of drag that hurts you upwind, and it doesn't always add much downwind - but when the spinnaker is really working, it's REALLY working!

    It's a really interesting topic and it would be great to get more info.
  2. rcnesneg
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    rcnesneg Senior Member

    I guess these guys are running at much higher apparent winds than I'm used to. My experience is limited to about what you get on an old beach cat, those get a lot faster if you put up a spin. I suppose at some point, the apparent wind increases enough that the spinnaker is no longer effective, so then the single wing/sail is the most efficient and as a result, the fastest. Am I right?

    Also, on the A class and C class, I realize they aren't allowed to run a spin, but if they did stick one on, when would it help performance at all, or would it at all?

    Edit: CT249 just answered the last question. Only 2%? That seems awfully small, but I guess it's pretty easy to see it when you get top notch guys racing each other. What about USA17? Did they use a headsail for downwind work?

    Edit 2:
    It appears that USA17 does have some sort of a downwind headsail. Looking at the camber in this picture, I would say that is definitely a downwind sail.


    Also, Hydroptere, the king of apparent wind, has at least two headsails, I suspect one for upwind, and one for downwind. This one seems to be bigger than the smaller fractional jibs I've seen, so I suspect it may be a downwind sail, and it appears as though she is on a broad reach as well. What do you guys think?
  3. waynemarlow
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    waynemarlow Senior Member

    Certainly in short leg racing its a no brainer. The kites go up and start to immediately make good VMG to the bottom mark, flying a hull someway further down the track. The uni boats such as an A have to first heat the sail up by bearing away less, pick up one hull and then start to make toward the bottom mark. From my experience I would lose 2 or 3 places on my A at that point against the F18's and Hurricane 5.9's I was racing against as once underneath you they can simply hold you at bay as the speeds were quite similar.

    Out of frustration I fitted a F16 spinny to my A and ballasted up the overall weight to maintain my handicap rating. Certainly now we are on a level playing field and my race results have improved dramatically.

    But my A is not yet fitted with foils and I would suspect that the foils will bring the apparent wind so far foward that it will fold the front of the spinny. Which is exactly where I have ended up, the F16 spinny worked really well on the slightly fatter and shorter hulls which seem to have enough drag to allow the the skipper enough time to constantly tighten the sheet as the speed builds up. On the more slippery A I am having real problems with the boat surging foward so fast that it over runs the leading edge and the spinny folds.

    I tried a very old full head spinny I had and although it is slower over the water, oddly enough it is faster overall, mainly due to the fact that you can steer the boat across a much wider range of angles, when you have 30 other boats in the same handicap race ranging from lasers to Nacra 20's you very often have to alter your course to avoid other boats. A spinny that has a very narrow wind range can be a real pain in this situation.

    One thing for sure though is the sheer "grin factor " a really nice spinny gives when out on the wire doing a steady 20 + knots for long periods. My favourite race of all time was a long race out to a coastal bouy, it took nearly 5 hours to get out there, but on the way back we could fly the kite out on the wire heading straight for the finish. 40 minutes and we were home. What a buzz.
  4. Doug Lord
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    Doug Lord Flight Ready

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  5. Erwan
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    Erwan Senior Member

    In the early 90's tests involving A-cat + kite vs basic A-cat shave shown that the kite improved performance by 10%. I think it was a 12 sqm kite area

    For the tests, crews tried to gybe, more or less, at the same point.

    But it was "middle thing" sailing at this time, we were not sailing "wild thing" yet.


  6. rcnesneg
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    rcnesneg Senior Member

    So long story short, for those of us who aren't sailing with rules, it's fastest to run a rather flat screacher for more power downwind, although it is more work.

  7. waynemarlow
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    waynemarlow Senior Member

    Is it more work, yes and no. Certainly from my experiance, yes it is more work to get the spinny up and down, but good systems such as the F18 and F16's have evolved, mean it's just 5 handfuls of halyard sheet and let the mast rotation fully off. Certainly the single handed lads can do it pretty quickly,why not the duals.

    Whilst underway the main is cleated with the travellor just dropped 20cms or so, yes the main is on nearly on as tight as upwind, the main supports the whole rig and many a mast has broken when the wind gets up and the less knowledgable skipper starts to let the main sheet off thinking it will depower the sail.

    No it doesn't make the sailing more difficult, once that 20 seconds of high intensity of getting the sail up is over and the skipper has learnt the art of filling the sail and then bringing the boat up onto the wind to heat the sail up and lift the windward hull, the speed will rapidly rise along with the grin factor and the boat will settle into a one hull dance downwind with the helm steering the boat to maintain the incline of the boat. The crew has to sheet in and out a little to maintain good sail shape.

    The F16's seem to be starting to drift away from really flat spinnys apart from the top racing teams, the flatter the sail, the less angle of wind they will operate in and the greater the skill needed to sail a good heading as well as maintaining enough drive in the top part of the sail to enable the windward hull to fly ( sitting flat with two hulls in the water is just slow ).

    With a well set spinny on a long sprit it is surprising just how much lift from the sail there is. If we couple in that the hull is now at about 15 - 20 degrees we also get a very long foil section also giving us upward lift meaning that the once problem of the Uni sail of pitch poling, has virtually disappeared.
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