Right, but to make the experiment fair you would have to add the same area to the main of the uni, unless both boats are overpowered already. There is no proof in any of these arguments, just examples and applied logic.
I am certain there are crossover points on the performance plots for both types of rig, and I have some toughts about where they might be. But until someone do the tests and produces some real numbers.. 'nough said.

I still think doing a carbin fibre RIB is outrageous, but nobody seems to have notices in all the uni vs. sloop noise.

I don't do RIB's !

Besides, it is just another example of carbon fetishm. Hardly a new discovery with Marstrom

Wouter

Dear Wouter, why do you constatntly say the sailarea on the A class is rather small and uses that as an explanation why it has no jib? In relation of sailarea/weight the A cat is having the most sailarea compared to it's weight of most of the boats discussed. For the same reason, at 1bft adding a jib might increase the upwind speed of an A cat, from on +2bft I am pretty sure the jib will slow you down as you are fully powered up already without anyhow. Downwind a spi is more efficient than a jib, so if we discuss outside class restriction, with any boat you would go for a spi.
F18HT shows it as well as the earlier Ventilo 20 (which regulary outsailed the Tornado).

A cat 75+75/14 (m²/kg)=10,7
F16 uni 105+75/15 (m²/kg)=12
F16 sloop 105+75+75/18,7 (m²/kg)=13,6
C Class 130+75+75/25 (m²/kg)=11,2
F18 180+75+75/21,1 (m²7kg)=15,6
Carbon RIB (for Rolf) ;-)
M32 ?

I'm not saying a uni-rig is without advantages; Hell in 60 minutes I'll be landyachting across the beach using a single mainsail.

The whole point of the exercise is to put some reality into the myth-making that happened around the uni-rig properties.




Actually it doesn't, not even by a long stretch. You are forgetting the spinnakers that many boats nowadays have. I mean, EVERYTHING is counted as sailarea or nothing is. On larger boats you have the code 0's and screachers that can be set even on beam reaches and low upwind courses.

When looking at spi-less setups there are also very simply counterexample in the beach cat field,

18 sq. 75+75/18.0 = 8.33
F16 sloop 1-up 107+75/18.7 = 9.73
A cat 75+75/13.94 = 10,8
F16 uni 1-up 107+75/15 = 12.1
C-class 200+150/27.87 = 12.6

Interenting to note the C-class specs !

Actually even the old (underpowered) geezers, when sailed singlehandedly, are not that far off the A-cat/C-class specs.

Hobie 16 150+75/19.5 = 11.5
Hobie 17 sport 150+75/18.86 = 11.9
Prindle 16 135+75/17.34 = 12.12
nacra 5.0 147+75/17.82 = 12.5

Now how many of us have singlehanded sailed or raced boats like the P16, H16 and nacra 5.0 and others in the past, over a wide range of conditions ? I think we can all attest to the fact that they were easily enough controlled. Basically all Hobie 16 that are singlehanded just HAVE to fly the jib as on that design the jib luff is also the forestay.

Now I have singlehanded the F16 singlehanded as a sloop as few times and it is pretty calm and easily controlled that way. Lots of power low in the rig giving a stable consistant drive.

And I would actually argue that boatweight is not very important when analysing heeling and righting forces. A better comparison would be to look at sailpower relative to the product of the width of the boat and the weight of the crew. Why, because even on a singlehander the boatweight is only contributing about 25% of righting moment.

When looking at the A-cats and F16's the difference in boat weight is 43% but the difference in righting moment is only 19%.


So actually when looking at the real heeling moment estimate (boat weights included) then some of the other boats mentioned so far have higher sail area to righting moment ratios then the A-cat has. And that makes the A-cat relatively underpowered in my book; note that the F16 is the only MODERN boat in the following listing next to the A.

F16 396/18.7 = 21.2
Hobie 16 435/19.5 = 22.3
Hobie 17 sport 446/18.86 = 23.6
A-cat 334 /13.94 = 24.0
Prindle 16 423/17.34 = 24.4
nacra 5.0 446/17.82 = 25.0
F16 396/15 = 26.4





If there is no restriction on the total amount of sail area that can be had then we see sailboats (not landyachts) with a sloop rig and a spinnaker.

Indeed, the spinnaker makes the jib almost negligiable on the downwind legs but it doesn't affect the jib added performance one bit on reaching legs and on upwind legs. Basically, adding a jib costs you nothing on the downwind legs but still increases performance on all other (non-spi) legs.

Wouter

If this is a true statement then sailing a Hobie 16 without a jib in say 5+ beaufort winds (=overpowered) should be faster then a similar crew sailing the sloop H16 in the same conditions.

I know you sail Hobie 16's Hakan, so don't take my word for it and just try this one time. And that goes for everybody out there. Just try it yourself. You'll all see for yourself what happens in real life.

With respect to A-cats, I have the exact opposite opinion :

An jib added A-cat in 1 bft will not show significantly improved speed in any way. This is because of the way the wind is made up at these low speeds, laminair flow patterns. In effect the range of height were the jib is there is simply very little energy (windspeed) that can be harvested. OVer 2bft the winds switch to a turbulant make-up and energize the layers much closer to the watersurface, now the jib will start pulling and add performance to the whole boat. In big winds all the depowering is done by losing drive high up in the rig which means that the top of the mainsail is switched off. The jib will in these conditions just continue pulling at full throttle because its heeling leverage is so small that it is pointless to depower it. The fact that at big winds the leech of the jib is adjusted as well is the result of the mainsail trim having been altered and the arrive back at the optimal interaction one has to adjust the trim of the jib accordingly.

Wouter

I want to end my postings in this thread as I'm in danger of rehashing my points endlessly and I got some stuff to get done; like repairing some landyachts. By the way Dirk, you are warmly invited to come and join me at landyachting some time.

I just want to say that this whole discussion is just about nuances and that even its heated status does not deminish the A-cat design and A-cat class in any way. The setup they have now is the best that can be had under the specifics (limits) of their class rules. The heated discussion about unis or sloops doesn't affect them as it assumes that the design is unlimited in any way but the need to maximize speed around any given race course. Class rules very much go against such a free environment and so too the A-class rules. Otherwise the A's would have fitted spinnakers a long time ago.

I just hope that readers have read the posts with interest and have looked at the situation from several different viewpoints after making up their own minds just as the designers of IDEC2 an the new C-class champion Alpha have done.

I hope to have argued convincingly that sailboat design is simply too multifacetted to be able to capture it in a few simple design rules. Of which of course, "uni-rigs are best" is one such example. The other of course being that "Full foiling is fastest". I think the recent C-class match where the real racing was between the non-foiling Cogito and Alpha has shown that it is just not that simple. You can't just look at the results in say the moth class and then argue that the same will hold for all other classes. Again, class rules do play an important role in how the fastest setup inside a given class will look like. As such a different set of class rules can easily favour another setup. I hope to have convincingly argued that part of the situation.

Good luck to everybody and have a excellent weekend.

I'm going landyachting now ! (where spinnakers and jibs haven't been seen for centuries ! )

Wouter

This discussion reminds me of this Monthy Python sketch:
Monty Python - Argument Clinic <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />

Wouter the 18sqm weight is 170kg..

Kinda makes a big difference!

That is the NACRA 18 square. This is a different boat then are found in the 18 sq. class. It was mainly sailed in USA and the lightest full carbon boats were very close to the A-cats in overall weight even when being over 3 mtr wide. Now the class is dead.

Interesting detail is that Wild Turkey was the first non C-class catamaran to fit a wingsail, it was an 18 sq. boat. The NACRA 18 square never got passed a large roached pinhead sail.

Wouter

Well if it's dead, then what is the point of using it?

thanks guys

learned a lot from this thread

will be interesting to compare sailing with and without jib on our smallish lake this summer with this thread in mind

Hi Erice,
be a bit careful when you compare the boat with or without the jib. A boat designed as sloop will work best as a sloop, if you remove the jib you will get a lot of weather helm due to too much load on the rudders, and the main needs to be cut differently if it shold work alone without the support from the jib.

/hakan