I know. I would like to understand the physics a little better. Maybe a designer will come along that can shed some light on the subject.

FWIW.... I just finished my first regatta in CRAM. I have never raced against any A cats before and I was surprised I was able, to a large extent, keep up and point with them upwind. I was not able to get them all downwind. I got a decent number of them. The A cat sailors in this bunch are no slouches. I used to think that 2up was the only way to go, but I am not sure anymore. I like sailing solo better anyway.
Btw, CRAM is a great bunch of guys. I look forward to sailing with them this summer.

Hope you can make it to Racine in August. We have 6+ F16s and growing in CRAW. A bunch of us will likely also make it to Captain Jack's in Muskegon.

I'll probably be at Caseville, Muskegon, and possibly another one.

Not sure I will be able to make it over to that side. already pushing my luck with the wifey. I am doing Bay City June 2,3 and NCYC 23,24. Caseville on July 21, 22 is a possibility

An A Class is a lot quicker than an F16 or F18 upwind. They sail about the same speed as a T with more height. The A does have the extra waterline length and the design is all about low weight, low drag and low displacement. Everything from the rig to the hulls are optimised for this. Don’t forget that most F16 uni's are a compromise between sloop and uni hull design. 2 feet shorter, 32 kg heavier and a shorter rig.

As for downwind, the new A's are now keeping up and even beating F18s downwind. It is not just the curved boards, but the stiff hulls, flexible (fore and aft) masts and incredibly powerful mains that are allowing these boats to trap downwind. Whilst you are setting your kite, they are shooting of in the sunset trapping downwind, not that you will be anywhere near them when they turn around the top mark.

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The physics are simple to explain, but opinions are all over the place. It all comes down to what you believe the most.

Theoretically, a sloop boat is faster then a uni allround, that is when considering everything else equal. However, most boat also differ from eachother in several important aspects and that makes comparisons problematic.

Physics,

A sloop rig can always fly MORE sailarea then a uni-rig. On anything but an upwind leg where angle of attack is important the boat with more sail area wins (assuming equal aspect ratio's, luff length and tipheight). Fitting a spinnaker to boat versions reduces this performance gap. Making the sloop boat clearly favoured on a reach and leaving the conclusion still open on the upwind. Downwind is pretty equal now.

On the upwind leg the balans may turn either way or hang flat depending on the details of the design. Sloops point lower but get more drive low in the rig and are easier to not stall, an inexperienced crew can get more performance out of a sloop then a uni. More drive means more speed and if that speed compensates for the lower sailing angle then both boats have equal vmg which is what makes you reach topmark first. F16's are counting on that particular aspect to a large extent. However it does assume that both rigs have rerceived sufficient or equal amount of development. It is probable that sloops have reached alot more development over the years them uni and lots of sailors are soloing their sloop rigs which is some drawback on performance.

The jib is not a hinderance on the upwind leg as many will claim. It does smooth out the flow over the main and will have it producing drive more consistantly , especially when the rig is moving about in waves or when the wind fluctuates. Also, the jib can operate well as surprising low angles of attack because of the interaction with the main. In affect the jib is in the updraft zone of the mainsail and does not nearly need as much AoA as a single sail does. the hit on pointing ability is therefore rather limited. A unirig needs an apparant windangle of about 20+ degrees where a sloop rig needs about 26+ degrees. Assuming as sloop sails at 45 degrees to the wind and a uni at 39 degrees then the uni rig gets 10% more saildrive. 20% additional sailarea will speed the sloop up sufficiently to equalize vmg , 15 sq.mtr times 20% = 3 sq.mtr where the F16 jib is 3.7 sq.mtr.

Do you understand the balancing act now ?

Ofc ourse other smaller factors are also at play like righting moment etc but I leave these out of the discussion for now.

Righting moment is however important and that is in my opinion the largest factor in creating difference performance between sloop and uni f16's (text above refers only to sloop en uni boats in general with all else equal).

Basically I banked on the uni being faster downwind then the sloops here becaus of lightweight and ability to fly sooner and sail deeper. With an optimized uni sail the loss on the upwind will be limited and subtracting these from one another will go a long way to equalize both F16's but of course never fully. In sub trapeze conditions I expect the uni to be slightly faster and in big wind to be slightly slower, in the medium stuff it is a fine balancingact.

That is the theory and consult Marchaj, Bethwaite, Ganty and other books for the details.

First point of call for any solo sailor is however to buy a dedicated uni sail for his F16 if he wants to race often that way. It needs to be latter all over and fuller in the part where he jib flies. It may also have a leech that opens more easily to spill air (at a lower righting moment level). All things a sloop main will not have. This alone will go a significant way in getting max F16 solo performance. The rest is learning how to sail it properly since their is no jib to help you trim the main or point.

Agreed but that has taken nearly 30 years of development. There is now quite some development going on with the F16's, we are starting to opitimise the boats for weight and drag. With an extra 1M in the main and 3.7 in th jib and only 1 1/2 ft shorter we should be fairly equal if not ahead as the hull drag is optimised better. The learning curve of the A will benefit us greatly and will shorten ours.



Yes off into the sunset for the first 75 metres and then the F18's and F16's are up and running faster and lower, it doesn't take long before you can reel the A's in. On short course racing its normally pretty even by the time you get back to the start. At a recent handicap race where the A's were starting, it was noticed a ShadowX with the new large kite ( virtually a F16 ) could reel in the No 2 in the European A Class downwind enough to handicap out as winning the race. That Shadow sailor is a very good sailor but is he comparible in skill ?

The other thing to contend is that very few people can trapeze downwind consistantly sucessfully on an A, you only have to look at race reports where the worlds best all have spills of some kind, sometime in an event. On an F boat most people can trapeze downwind under spinny, it is a far far easier skill to learn for some reason.

Not dissing the A's, they are a wonderful boat, very refined and lovely to sail, but I think they may well be knocked off the top perch fairly soon, by any of the F16, F17 and F18's once developed a little more, being more than an equal match.

Thanks Wouter.

I've been wondering how 'fast' it would be, if you took the current 'hot' A Cat hulls, chopped a little off the front and back, chop a little off the mast, add a spinnaker and maybe some 'corrector weights' to get it up to F16 min wt. specs, then raced it Uni, ie. zero jib hardware.

I think it would be an interesting experiment...but expensive, more so, if it didn't work out to be at least as fast as one of the 'Stock" F16's.