New A Class Catamaran Rig: Square Top Jib

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Peter, from what I've read thru the bs on Sailing Anarchy, Smyth has convinced himself that you are right.

Some thoughts:
-- If he had a balance problem,he could move the daggerboards forward which would help in a number of ways particularly if he was using lifting foils. Pioneered on the Arc 21 and maybe others. Bill Roberts uses his concept of "shared lift" on the Arc 21 which places the daggerboard(smaller than usual) forward of the front beam. http://www.aquarius-sail.com/catamarans/arc21/index.htm
-- The designer of the Swift Solo(singlehanded Skiff) came up with an excellent sheeting system that allows the main and jib to be trimmed with a single sheet. Has a "relativity control" that allows the slot to be adjusted. I used it on my boat and it works well.

click on image:

 

Swift Solo System

Yes I've admired that system and would do it next time I had a small dinghy suitable, but onward to Wings! Re: Arc21 - we catamaran sailors have not explored properly underwater foil configurations. There is a lot of scope for canard type fwd foils for windward control and tacking ease. But usually the damn rules are written to restrict controlled surfaces and number of surfaces. Image if Boeing had rules that they can't have trim tabs on their rudders! or no airolons on their wings? We now have situations in various classes where we allow banana boards which are very expensive and fiddly and not much better than straight boards yet they were created to get around the max width rules. If we said the max width was only on the hull then we could use an easy straight board to acheive the same thing. Its about time we let physics and good engineering develop boats and get away from prescriptive rules. Peter

 

AC Wing Masts

Gary Baigent - By "4 element" do you mean 4 elements or two elements each with flaps? A proper multielement 4 element rig will give huge lift and would need to be much smaller than the current AC72 wing profile would allow, interesting when teams would start asking to use smaller "sails". But what a mechanical beast that will be but its the future. Peter

 

hi Peter, well, that was just me looking too far ahead - I'm thinking, once the AC72's get bored with their 2 element rigs, real sophistication will appear - meaning 3 element rigs, like Lindsay Cunningham C Class designs, but with sliding elements and "zap" flaps; maybe they could go to even 5 elements ... and then downwind, all the sailmakers will begin crying into their cafe lattes, because that will be the end of soft sails ... because the multi-slotted wings will develop tremendous lift ... and upwind, the slots will slide together or away and the rig will become aerodynamically clean. I bet the design engineers (and crazies) will be already thinking along these lines.

 

Hi Gary- I've been working on twist control and multielement control. Being a design engineer (and perhaps crazy) been thinking about this for some time. Lots of thought balloons and semi conscious ZZZZZ's. Quite a problem. I think twist is out for the big rigs. The loads required to twist rigs much bigger than a C=Class get quite big. So if twist is the goal we need very clever "soft" structures or multi multi element type rigid wings. I'm not sure if the C=Class rig with the small panel 2 is really a 3 panel design. Some serious definition work has to be done by the aerodynamists for wing sails! Would be good to be in Auckland to see the AC45s! Cheers Peter S

 

twist

twist control model - cheers Peter S

 

How about the J-90 Eric Hall was experimenting with a uni-rig, ....
...Eric is now on his third-generation, free standing ,carbon wing rotating mast, with a una-rig mainsail. His “ thought process (and maybe not entirely logical) was: If biplanes became monoplanes and monoplane wings shed wires, why not an unstayed una-rig upwind” Boy, you would surely think this was the ideal upwind rig. In responding to an inquiry on upwind performance, Eric responds, “ first, of course, the boat would be improved upwind with a No.1 jib. Generally, we could not point as high as the others here (Block Island)....

http://www.boatdesign.net/forums/sailboats/analysing-upwind-performance-5681-2.html#post35039

 

Twist Control

Re: AC72 Artemis wing rig. I watched a video interview with Paul Cayard from Artemis and they plan to use hydraulics to control their AC72 wing. They will have two sailors pedaling or hand cranking hydraulic motors full time. The rules state that there can be no stored energy so the "grinders" will be running all the hydrualic systems. This makes sense as the loads are huge and rope tackle won't be up to it. Its a bit of a shame having to go this way with human engines but we are close to this anyway with big sailing rigs. Peter

 

G'day 'petereng'. Re; "So if twist is the goal we need very clever"soft" structures or multi multi element type rigid wings."
So are we - going 'back' to the future? Semi soft structures might be a good place to start. Variable - wind strenght controlled - wing mast - was/were around back in the mid 60's. Successfully won many very competitive races over many years. Maybe one day someone really smart & high tech will do it for bigger & faster yachts. That'll sure leave me out though. Ciao, james

 

Not intending to revive and old thread, but I have a major question regarding the C class and A class cats. I have noticed that none of them seen to run jibs, or even spinnakers. Jibs i could understand dropping, but why spinnakers too? Is it because of the huge apparent wind? If so, why do the AC72s, AC45s, and flying phantoms have spinnakers?

Would spins make the A and C class cats faster, but they just leave them off for some reason? Why don't they use spinnakers?

 

The A & C class have a maximum sail area rule so if you had a spinnaker its area would have to come off the mainsail/jib. They used to run jib/spinnaker but just a main is faster. The other boats you mention have a rule stating that a jib must be used. Please note in last AC TNZ lost its jib and went faster not slower. Its better to consolidate sail area into one sail so you consolidate LE, and top and bottom losses ie the overall efficiency goes up. cheers Peter s

 

These boats are sailing upwind even when they're going downwind. There is a lot of theory around but the AC 72, new AC 45's and probably the new AC 62's all use small jibs. When you consider the level of design talent on those boats you could conclude they know something that some others don't......or not. Spinnakers/screechers/Code Zero's work on some foilers like the Flying Phantom(lower left-Oracle version).
All the AC 45's below are brand new or close thereto. Oracles 45 was sailed for the first time yesterday. Lower right=AC72 with a screecher (probably) :

 

So would an A or C class go faster downwind if you put a spin on it? As for the phantom, I wonder why they would have put a jib on it, are they trying to conform to some class rule as well?

I find it hard to believe that you could go faster downwind with no spin than you could with a spin, yes, the drag increases, but you get a lot more power, right? Is this something we should be applying to our high performance boats, like Doug's trimaran for instance?

 

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You need to do more research-particularly about apparent wind sailing. It was mentioned earlier in this thread and I saw it live: when Oracle 17 THE TRI was racing Alinghi THE CAT for the America's Cup, they were nearly side by side and Oracle dropped her jib and it was like lighting afterburners-she just went much faster. It depends on the boat, the speed, the conditions and a whole lot of factors. In some cases like the C Class and A Class they are limited in sail area so they can't be using downwind sails even in conditions it would help. Other boats use what the scientists say they should.
I had a Code Zero made for my test model to help it foil in real light air-but it foiled in 4-5mph of wind without it so it hasn't been used. But Dan and I will try it sometime even though we don't need it to foil but it may help with faster speed in light air.

Code Zero =white:

 

RC, this may help: http://www.sailbetter.com/apparent-wind/