Alan, here another nice video for your investigations ;D
:lol::lol::lol: X-Ray unit kaput !!! information over-load :p…but seriously jealous of the good sailing weather you have in Rome for this time of the year …:sad:
Yes, Sara after some regattas, preferred to tan in swimsuit!!! Hot day!
However after this day, I finally had the possibility to test SUI-102 vs SUI-100 (with new sails, mainmast and bulb) and at the end now i have a lot of informations to analyse: SUI-100, is much more fast up to 2 knots wind speed, especially sailing close to the wind. Beyond 3 knots, SUI-102 is faster. Now I have to understand why…
some other nice video:
http://www.youtube.com/watch?v=uzd3jvGFntM
http://www.youtube.com/watch?v=XYAX8M2ry0w
http://www.youtube.com/watch?v=c8V6v17cCk8
Matt - possibly a flatter sail (less camber) on SUI - 102 when wind speed increased?
Flattter sail = more speed, less power.
Lay both boats on their sides, hull on one chair, mast tip on the other and bring boom to close-hauled. Then measure the camber in the main sail of each and compare. Possibly the #102 boat has more outhaul (and/or downhaul) then the #100 boat and has a flatter sail.
Only a thought. Dick
Which boat was Sara skippering ? …a bikini can make all the difference 
Either way two fantastic boats Matt !! … hey if you like to post some side by side pic, weight, dimensions, sail plans, ballast comparsions etc …we can “try” and help you understand the micro 1 knot differences … promise no X-rays ok ! :sly:
Cheers Alan
Thx for compliments Alan, on my opinion Dick has complitely reason. The difference in performances is due 99% by the different sails: -1dm2 and flatter sails for SUI-102. This set-up is very good beyond 2/3 knots but under I had problems often and now I understood why. Now I seen the great difference, probably will make a new sails set 1 for SUI-102 with a little bit more surface and less flatter. Probably I will lose a little bit beyond 8 knots but under this range I hope to increase a lot the performances.
Ah back on topic RIG & SAIL FINE TUNING and coming to part two of this thread now…SAILS
With quite a number of new people on the site I thought it might be worth looking at various choices available for IACC 120 class; let’s start with IACC 120 Class rules version 1.3
C.7.2.1 SAIL AREA
RIG 1 80 dm² maximum - 73 dm² minimum
RIG 2 60 dm² maximum
C.7.5 USE
(a) MAINSAIL The LUFF shall be : 1750 mm maximum
(b) HEADSAIL The Headsail forestay top shall not be above 80% of the Main Luff length
© GENOA As above for the Headsail forestay.
G.5.2 SURFACE
The Headsails surface shall not be lower than 35% and not higher than 55% of the Mainsail surface area.
The surface projecting over the Mast is not calculated.
The Genoa Luff length shall not be greater than 80% of Mainsail Luff length
In my quest to learn more about what is required to have a competitive package, I have noticed that there are quite a few variations that are used in 1) traditional triangular mainsail head and 2) different sized square headed mainsails. (see attached pic)
I will focus on 78 dm2 sail plan used for light to medium airs (0-12 knots) from what observe there are three ways to can configure the main: a taller mast, a longer boom, or more area in the roach.
As we all know sail shape of a sail is seldom a perfect triangle, different sail plans have different variations of extra sail area on the leech, outside a line drawn from the head to the clew, called the roach;
I’ve been using 120 mm square head main sail, one of my problems is that mainsail has too much twist most of the time. In fact one of the problems is keeping them from twisting too much in light and medium air. With the extra area in the sail, and the greatly increase leech loading, to support the square top on a fractional rig the mast tip has to be very stiff.
Mast tip deflection either aft or sideways will allow uncontrolled leech twist, hence another reason to have jumpers with square head main sail, we touched on early with my new rig set-up.
A square head mainsail requires more trimming and slightly different fine tuning trimming techniques. In conditions where you are not overpowered you will need much more vang tension to get the entire leech to stand up.
When I look at the Italians, the guys in Rome seems to prefer more square head main sails (some very aggressive sail roaches which I don’t really understand) where as the guys in Milano area prefer the more triangulated main head (less square) and the Milano’s seem to win the Italian Cup ever year … so far !?
My question: what are the basic differences in performance & tuning of triangular vs square head main sails?
Cheers Alan
Hi Alan,
These are my thoughts.
Sailing an IOM, the amount of twist in the main is a crucial boat speed factor. Too much twist and you lose many boat lengths. When I looked at those videos, my reaction was ‘too much twist’.
The twist on a triangular headed main is much easier to control than the flat topped main. The effects of mast deflection, while still there are less pronounced.
The area of a flat topped main breaks into three shapes. A tall thin rectangle behind the mast, a triangle behind the rectangle, and a roach.
Given that is is hard to control the square topped main, I would take out that rectangular area (going to a triangular shape) and add that recovered area to the jib. (While remaining within the class rules.)
So I think that the fastest. most controllable rig is a max luff main with triangular head and as long a boom as necessary for maximum area. Combine with jib of max hoist, max luff length and set the foot to get the max area allowed in the rule. While overlapping head sails offer free area, they are not efficient off the wind (big boats take them down and use spinnakers), so a jib with a boom is more effective all around.
The square headed rig may give a scale/realistic look, but a fully controlled rig will be faster.
John
Hi Alan and John
ther are many justifications that personally I do not understand as John said.
About the choice of main shape.
1- just fashion to imitate the real ones
2- the assumption that at the top, up to 180cm from water, there is better airs ( false) and the upper surface will catch more wind
4- the square shapes produce drawbacks : difficult control of leech twist, and more seriously shift of the CE toward the height
5- some used shorter mast for easy the transport with consequent lowering effect on the CE .
As Alan says and confirmed by John, the triangular shape produce better control and lower the CE expecially if it is accepeted a wider boom
At the end the overall efficiency will increase except if the twist effect is better controlled otherwise will produce more arm then good.
Cheers
claudioD
John & Claudio, I agree with you both and now tending toward the more triangular main sail head shape.
Further, I was comparing different images to my ETNZ and think I found a major mistake on my part during construction, which could explain why I was having diffculty controlling the leech/twist :rolleyes:
I think I had not positioned my vang far enough along the boom from the mast, and had not enough leverage on the boom, you will see in attached pic that ETNZ position is roughly 20% of boom length, compared to my CHN 39 which is more in the region of 35% of the boom length.
Trap for first time scratch builders, especailly if your using square head main with big roach ? :scared:
Cheers Alan
I like this sequence of photo’s which taken over approx 50 meters in Ravenna, shows the triangular main sail is not heeling as much as a square head main in heavy air (as per Claudio’s points) check out the speed/distance gain !!!
Have no idea of the sail area or set-up on either boat…but damn impressive
Cheers Alan
Hi all,
I didn’t understand everything concerning twist control. I think that the main problem is the top of sail twist (that is not controlable). On square sails, the top is “free” to move and creates a disformation of the “wing” shape of the sail. So there might be a loss of power. It may be stupid but some other guys here could explain it better than me.
Regards,
Paulin
Hi Paulin,
Yes you are right, but big boats can control sail twist various ways…attached few photo’s:
-
RC 44 with heaps of twist, you can see how the sail twists going from foot to the head of the mainsail, maximising power going up the sail.
-
Full AC boats you can see mast man or spotter at top of the mast, part of his job to to spot wind shifts & in light air other part of his job is to kick the head of the main over when tacking in light airs.
Why do they have to kick the head of the main over ? when you look at the battens at the top of the sqaure headed mainsail they are in pockets & they can induce bend into the battens to have optimium sail shape at the head, in light air the batten bend will not be pushed out by wind pressure alone, so the mast man needs to kick the battens over.
Cool job 50 metre’s above the water !!! :icon_tong
On our RC boats, battens are important part of holding up the head of the main also, but too stiff and they won’t flick over in light air, so we rely on controlling main sail twist with the vang.
Claudio’s point, if I understand him correctly is that: with IACC 120 trying to imitate the real AC sized boats and the false assumption that there is better air 180 cm off top of the water is that they suffer seriously trying to control mainsail twist with just vang control.
Once you have set the vang on shore, they is no possibilty to change main twist when the boat is on the water (crew not allowed) so in heavy air when you are wanting to flatten the main (minimum twist) you suffer from having too much air at top of sail (CE moves up the sail) which results in more heeling.
Cheers Alan
Alan,
I agree with you for all…but I use large mainsail head with success… so?
If… IF… you have a perfect head control thanks to the perfect rig quality and sails quality and shape, you can have an advantage using it because the CV sails, is 5-6 cm lower. That means power, stability and speed. Of course it is not easy to do a fine set-up. You remember in Ravenna, saturday I used a wrong maisail head set-up and I lost the first position…but…however I arrived second…so the low CV benefit allows advantages ALWAYS also if you don’t have a perfect mainsail set-up, especially sailing downwind. Thanks my sails downwind and 90° to the wind (I don’t know in english the word sorry), SUI-100 was much much more fast than other boats…
If you see one of the first video that I posted in Ravenna fleet regatta at the end of one, you can see a transition to the boa and a long sailing upwind between Shosholoza and Alinghi and you can easy check my problem to sail close to the wind as Luca, cause the mainsail head too open, but grace to the low CV point I can have a major speed so at the end the distance is the same…
Cheers
Matthias
Hi Matt …wondered how long it would take you to join the discussion 
and there is no question that you sail SUI 100 with great deal of success in Rome, but when it comes to the Italian Cup, the guys from Milano always seem to come out on top at the end of the day …right or not ?
I’m just a taking a subjective approach and discussing it with the wisdom and experience of others in this forum, and I’m very happy that you are part of it.
Agree 100% it appears that a large square head main sail is much harder to tune right and you have no doubt mastered it with your low aspect sail plan, I’m just wanting to better understand it and I cannot so far, sorry but I’m am not knocking it, you are a winner and I’m not, but I will be perfectly open in saying that I’m not fully convinced that is the whole story either :rolleyes:
You’ve touched on SUI 100 ability to point very high and I’m of the personal opinion (as you know) that SUI 100 Jib set-up is the best on the planet my friend, and it may even carry most of SUI 100 advantages to what I see through my eyes against the disadvantages of the SUI 100 main, but it is only an inexperienced RC sailing personal opinion talking here, wanting to better understand some of the finer aspects of IACC 120 class racing…
Cheers Alan :zbeer:
Alan, the skippers from Bologna (not Milano ;)) use 6cm head mainsail because their great previous experience is from IOM class and M class where the sails used are only with a little mainsail head. So they know perfectly how to tune them.
Of course the phisic teaches that a high and narrow sail has a better performance but a sail is not a wing of a airplane, and the dimensions in elevation produces also some disavantages: High CV, mainmast weight, mainmast flexibility, principally.
Remember that Shosholoza and Bmw Oracle are good boat, but now my boats are faster and if they win is only because the skippers are better than me 
I would to show you a video of Ravenna where I joint some regattas only in heavy wind, so the hardest conditions for a large mainsail as Alinghi use. You will be surprised of the image results: on this weather Alinghi was much faster in downwind and pretty fast as Shosholoza sailing upwind:
http://www.youtube.com/watch?v=8Rc_YWAy9NM
Cheers
Matthias
You guys aren’t using battens up top to add camber, (or are you ??) so the flop over when tacking shouldn’t be a problem, unless you have and use a method to tie the battens in and make their tension adjustable to add camber up top. Seems most photos I have seen of r/c sails, show that battens are simply using flat battens NOT under tension, to support the sail area and leech that far up and out from the mast. Granted some use the uphaul/halyard further out on the mast crane to support the top of the sail.
Flat, under-cambered battens up top also reduce power up there as well as add to stability issues of heeling if wind picks up.
Hi Dick, Everyone is using battens with various application to the main, to my knowledge no-one uses adjustable tension battens, I could be wrong but have not see any. Main reason being that you need to sew a pocket into the main which is little more complicated for RC sails and then there is the question of added weight up high 
Attached is pic showing sample how battens are applied to IACC 120’s.
Matt, firstly aplogies to the guys in Bologna :drunk: stupid me
A great collection of vids demostrating SUI 100 superior boat speed both upwind and down-wind, thank you for sharing that with us, with your permission I would like to post my theory on what I think are the major differences there in boat set-up between SUI 100 with RSA 09 ?
Personally I think both boats have the highest skilled skippers in this class, both Luca & yourself, but I respect that you may not want to have open discussion on “my theoretical thinking on your different boat set-up” so I would like both your permissions first before posting.
By the way, who was that poor bugger which was de-masted :blkeye:
Cheers Alan :zbeer:
Hi everybody
I pick up this image from one of my books
The translation of the italian text :
“In a sail with low A/R ratio, the sail portion disturbed by vortex at the extremes, i greater than the one of a sail with a high A/R”
Claudio, is this for full size yachts, if so would you say that it applicable for RC yachts as well ?
Cheers Alan