WARNING - LONG POST
Thanks Barra and WP!
Mark, Yo and others - can I just point out that nothing I have written is intended to dismiss the mast-aft rig, which obviously works well for some people. My intentions are not to attack any rig or sailor, but to defend other rigs and sailors from attacks upon them.
Brian; I'm not an aerodynamics expert and therefore not qualified to comment on the technical merits of the Milan study. However, since I'm stuck at home with a cough, I may as well make some remarks;
1 - the authors do not seem to be balanced in their assessment of each rig in some ways. For example they say that in the conventional rig
"the tuning techniques required on the mast, the boom, the stays and the sails, need, to be effective, expensive equipment like additional tracks, sheets, vangs and the correspondent purchases;"
This seems to be biased. The two-jib setup also has a boom, it has as many sheets as a conventional mast. There seems to be no reason why their boomed staysail would not need a vang (all else being equal) and their genoa would have to be barber-hauled out or have its excess twist controlled in some other way when sheets are eased. IMHO their low-clew genoa would be fairly ineffective downwind because of twist, but that seems to be ignored. Their single-headsail rig has a long boom that would require some sort of vang and pose other problems - again these seem to be ignored in an effort to praise one rig and damn the other. They do more of the same, but I won't go into detail.
* They show the conventional rig as being tested when it is trimmed incorrectly, with a straight mast and mainsail reefed down to the same height as the #3 jib, which was not flattened as it really would be. Therefore the conventional rig was not being tested at its optimum performance.
* They ignore the important effects of headstay sag (which makes headsails harder to depower) and the ease of using mast bend to depower a main, which appears to be unfair to the conventional rig.
* There was no report on testing at wider apparent wind angles.
For these reasons, there is probably reason to doubt whether the study was fair.
2 - Tests are great, but the real world has shown many tests have been shown to be wrong in the past (see AstroSail for example, or the huge fracas about the 3/4 aft measurement under IMS).
These tests results appear to say that speed will increase around half a knot under the twin headsail rig, which is an ENORMOUS speed jump. If I recall correctly, this is a performance advantage roughly in the order of adding a canting keel. It's the equivalent of making the whole boat bigger by about 7 feet.
It beggars belief that the many, many thousands of sailors who have been involved in the sport over the years would have missed what would have been the biggest jump in mono performance in many decades. When races are won by a fraction of one percent, no one can miss an increase of about 7%. That's like having a Farr Mumm 30 that can just about beat the world's best Farr 40 OD around the course each week, or a J/24 beating a top Etchell or J/29 across the line every time they race.
For about a century, sailors have been REDUCING the number of headsails they use in many yacht classes. They have also spent decades testing sails and pulling them up and down while racing and experimenting. Thousands of people have lots of experience with staysails and cutter rigs, and (all else being equal) just about all of them have thrown them away because they have found them slower in reality. People note what happens to boatspeed when they set and drop sails!
If this study was correct, all the pros who have designed rigs and played with them are ****** who have not been smart enough to look at their speedo while they are out there testing sails and racing. Apparently this amazing stupidity has been existing since, for example, the J Class and 23 Metres went from three headsails to one.
How could it be that people went to all the expense of developing single-headsail J Class rigs
if the cutters they were racing against were basically faster? If twin headsails and no main make a boat 7% faster then why did the boats with one headsail beat the cutters? If these claims were correct, then decades ago the old 6 Metres with cutter rigs would have beaten the latest 8 Metres with sloop rigs - can anyone seriously claim that no one would have noticed such an bizarre reduction in speed from the newer and bigger boats? Was there some sort of mass delusion going from Keil to Cowes and all the way to Auckland, which stopped people noticing that their new rigs were dramatically slower than the old ones? Has this delusion continued to the present day, and stopped people who use cutter rigs in some classes from using them in other classes?
Every scientist I know of (and I'm married to one) would probably say that in a situation like this, where there has been years of real-life experience, such reality trumps experiments - and for decades reality has shown that cutters are NOT faster (all else being roughly equal) and therefore this test must not be accurate.
EDITED TO CONDENSE
