Steve,

Sloop rigged Taipan and Mosquitos are definitely faster then cat rig Mosquito in wind over 20 knots. While I may have beaten sloops in those conditions I certainly don't think its the norm.
Cat rig Taipan versus Cat rig Mosquito in wind over 20knots, I would expect to race with Taipan cat rig backmarkers and beat the first Taipan on handicap if VYC yardsticks are used.
As for the standard of the sailors I race against, they are club sailors like myself.

No more from me on this thread,
Darryn

Yeah, the cat rigged taipan back-markers are my benchmark atm without kite. If I can keep with them then I'll be happy.

The taipan sailors at the club have also said a mozzie will perform very well in a breeze. Now I've got to stop breaking the thing in a breeze!

I will post photos as soon as the mast is sorted.

Nick.

Hi Nick

Keep posting the information on your mainsail. This is definitely the right place for it. It's great to have someone making the effort to try out an idea like this. There's no other way to find out if it will work.

The Taipan is wider as well as having the taller & bigger rig. You are right that in most other respects it's like a Mosquito.

Mosquitos are competitive in a drifter, but as the wind increases bigger cats get on trap earlier and leave the Mosquitos behind. Once the Mozzies get on trap they are back in the race.

As far as performance goes, what we see at regattas in Victoria is:

• Cat rigged Taipans are definitely slower than sloop rigged Taipans once everyone is trapezing.
  
  
• Cat rigged Mosquitos are slightly slower than sloop rigged Mosquitos above 15 knots and in waves.
  
  
• Cat rigged Mosquito is faster than sloop in 10 knots or less.
  
  
• Well sailed Taipans are a lot faster than well sailed Mosquitos (note: despite the rumours even a Mosquito with a spinnaker can still be beaten on handicap by a good Taipan - see last year's
  Wildcat results).
  
  
• However,a Taipan that is not sailed well performs well below it's handicap and can be beaten around the course by a well sailed Mosquito.
  
  
• A Mosquito with a spinnaker is fun to sail in everything up to 20 knots (maybe more) whereas the Taipans do not want to use spinnakers in 20 knots (what's the point when you are already at terminal velocity ).
  
  

Thanks, Tim & Darryn for clearing up my misconception. We (the RSA Mozzies) had believed that your uni fleet would be faster around a course than your sloop guys, even if it was windy. We must have got that info from someone / somewhere, but these last two posts clears things up a bit.
Having said that, when our National champ sails uni in up to 14knots he is still damn hard to beat if I`m sloop, over 14knots it only gets a little bit easier to stay with him, and that includes us both on spi. downwind. But in over 20knots sloop is just so much faster.
Skill level still plays a huge role, as you said Tim, well sailed Moz can beat an average Taipan sailor, I have had Hobie Tigers behind me but then I know there is a difference in skill levels, it proves nothing about the boat`s potential.
Darryn, I was not questioning your integrity about finishing ahead of Taipan sloops in 20knots, just letting Wouter know that from what I`ve heard you are no slouch against the Taipans in these conditions.

Steve

Going back to the subject of sail twist with the fat top sail, I just found this recent photo of Gary on Altered.

What does everyone think? Right or wrong? Could he make this leech stand up? Would it be possible to over sheet it? Gary should be able to tell us from the mainsheet blocks, whether he has it sheeted in or not here.

Hard to tell without seeing telltales. I reckon it's under-sheeted, but I'm a n00b to cat sailing...

Nick.

Hi Tim,
As usual, a great photo of Gary styling on an awesome boat.
I think that he looks pretty much sheeted in max there, looking at the blocks. Most cat mainsails are designed with a certain amount of twist built into them, so if your leech stands up all the way to the top, you are in effect oversheeting the bottom 2/3 of the sail. I`m certainly no expert here, but from what I understand, twist is good, not only to depower the sail, but aerodynamically as well. Something about the wind higher up flowing faster than lower down, or at a different direction, whatever. Maybe the aeronautical engineer`s who visit these forums can explain it.
Looking at modern windsurfer rigs, the sail is designed to have quite a lot of twist, so much so that when you look at the sail on the beach, the leech is floppy, this depowers the rig before you have even sheeted in, but also has the effect of creating a large amount of twist. Now why would they do that if they could rather rig a smaller sail and have the leech stand up straight, it would still depower in the gusts due to the flexible mast. The answer must be that a large sail with a twisted off head is faster than a smaller sail with a straight leech. Perhaps in cat-sailing this is all different, maybe too much twist will hurt your pointing ability, but if your speed is much better you might still be first to the weather mark.
Just my opinion, so all those who have a degree in aircraft or sail design, feel free to straighten me out.

Mmmm, very interesting. The theory I have running around in my mind right now is that as the boat pitches and accelerates/decellerates over/through waves causing the sail to move back and forth through the wind, the apparent wind moves forward and aft very quickly, say through 10-20 degrees for every wave that is encountered.

So you need to be able to change the sheeting angle of your sail to obtain the maximum thrust from this ocsillating apparent wind. As the boat pitches backwards the apparent wind shifts aft a bit and as the boat pitches forward the apparent wind shifts forward a bit.

Changing the sheeting angle is very difficult, or impossible, to do fast enough on many boats. So another technique needs to be developed to allow the sail to operate efficiently at all these different angles of attack very quickly. Dinghies do it by pumping and "bouncing" the crews body weight through waves, although it is illegal, as this moves the rig towards the wind and counteracts the apparent wind moving aft as the boat/sail is pitching aft.

Cats don't tend to operate the main much upwind so a different technique has evolved, big head mainsails with the right amount of twist, not too much, not too little. With the right amount of twist, the sail will "on average" operate more efficiently as different sections of sail at different heights change between being highly efficient and then inefficient. So while one section at the top may be operating poorly, a section at the bottom may be operating highly efficiently. Then when the boat pitches the other way the top will start operating highly efficiently while the bottom operate poorly. But on average, a correctly twisted sail will operate better than an over-twisted or under-twisted sail. This all depends on the conditions ofcourse, if there are no waves, more of the sail can be in the best position more of the time.

The first principle to get straight is that the apparent wind oscillates/rotates across the sail as the boat moves through waves. A cross section of a sail works best (produces best thrust) at one angle of attack. Twisted sails have many angles of attack to what is referred to as the steady wind direction. All of these sections up and down the sail at sometime during the oscillation of the apparent wind, due to pitching, will be at their most efficient angle of attack to produce thrust. This means that the centre of thrust is actually moving up and down the sail with each pitch. Over time, this thrust will add up to be more than is produced buy a sail that is setup with too much or too little twist since both these scenarios have a section of sail that will rarely operate at its most efficient angle of attack.

This might explain why it is a common indication of a correctly twisted main that the top leech telltale should be flowing about 50% of the time. The top section of sail is only operating at its best angle of attack to produce thrust about <50% of the time (telltales will stream slightly either side of best angle of attack though). While the top section is operating poorly, the other sections of sail are operating efficiently. Imagine the apparent wind angle as it moves up and down your sail. It will tend to slowly move forward as you go down the sail and will tend to move aft as you go up the sail.

I might be a nerd and crunch some numbers later to see how much the apparent wind will rotate at the head of a pitching sail. That will give an indication of whether or not my theory is correct.

How this relates to square head mains may be that the sail area is distributed more evenly up and down the sail so the instantaneous thrust is pretty much the same during the tiny oscillations.

Be careful with my terminology, I have used rotate, move and oscillate interchangeably with reference to the apparent wind angle throughout the post depending on the scenario I'm trying to explain.

Excuse my long sentences, I wanted to get it out quickly before I forgot it.

Nick.

Just better clear something up about wind angles. The true wind is not changing direction significantly the higher you get up your mast. The true wind speed is however changing significantly, as you said, because of wind shear/the boundary layer. In other words the wind closer to the water surface is affected by friction and slowed down compared with the wind up higher.

Since a boat always moves at an angle to the true wind an apparent wind is created. Apparent wind is what you feel across your face while sailing. The apparent wind angle changes significantly as you move higher because the wind speed higher is faster. A thing called vector addition lets you calculate the apparent wind speed and direction very simply as indicated here:

Apparent Wind Calculator and Diagrams

The guys at the twisted flow wind tunnel are the gurus when it comes to apparent wind and required twist. There is a diagram that perfectly shows what is happening to the apparent wind at this link:
Twisted Flow Wind Tunnel - Auckland

Anyway, enough from me.

Nick.