hi guys, am just graduating form mosquito catamaran to a stingray caamaran. much the same shape (hulls like a tornado).
and some of the boats carry a standard shaped mainsail, and some newer rigs are running the big head or square top mainsails. my question is: what are the pros and cons of the squar top???
are they faster in heavy wind or lighter wind???
cheers

beg to differ on the turd polishing , myth busters busted that myth
square head on my boat seems much better all round for me

i look forward to hear the response of the guys who can really explain the technical aspects of your question, but from my experience i find the extra sail area on top leads to more power (not necessarily speed.. it depends how you utilize this power).

This is a great advantage in light air.. and i can handle it without to much problems up to 20knots.. above that i am rough handling my boat to keep it from capsizing and need to do everything i can to depower it (upwind) down/outhaul.. traveled out, jib furled... etc.

PS I usually solo my 5.5

I have recently acquired a pin top tornado sail that was cut for a prindle 18 (its a bit short for my rig) and i haven't had a chance to try it out.. but if all goes well... it will be my sail for heavy air (above 20)

I believe it was Dave Calvert that started the concept for windsurfers, before he started designing multihull sails.
The theory is you have a fuller, more powerful area of the sail up high for lighter winds.
Now, when a puff hits, because of the length of the batten sticking out from the upper mast, the wind uses that leverage to allow the top of the sail to blow off to leeward, thus depowering in the puff, lowering the center of effort, and also reducing the heeling moment.
Sort of an automatic transmission, it shifts to a high gear in the puffs, and when the puff subside, it shift down again for more power.
Add to that the ability to downhaul and it becomes even more useful.
And they definitely work much better than pinheads
Rick

It's more nuanced than the question asks. In terms of power, it is basically as simple as 'its windier up there' as there can be as much as 2-5 mph difference 25 feet above the water surface. Placing more sail area up top takes advantage of more power.

Now we get into nuance...Square top sails are usually designed to match the mast, which has a very dynamic interaction with the sail plan. The front of a performance cat sail is cut with a curve in the luff (the part that goes into the mast track) which, when the mast bends, allows the sail to flatten. Without going into a lot of detail (you can spend hours trying and still not be able to visualize the process until seeing it with your own eyes on a boat) the square top works in tandem with the cunningham/downhaul/rotator to impose a shape on the sail that is most conducive to sailing conditions. The square-top provides leverage on the top of the sail down from the mainsheet (think square top 'pulls more downward' vs than does a pin-head sail (think 'pulls more backward'), and is therefore able to bend the top of the mast more efficiently. The result is greater ability to tune the rig according to sailing conditions, and an edge on speed overall.

That said, I haven't figured it all out...

Hope that helps

Less drag for more area, higher up => better lift/drag ratio. A sail that is in my opinion easier to handle and sail well with.

The "automatic gust response" is fiddly to get right and depends on a lot of variables. That is not the main point. A more efficient and userfriendly sail is.



I dont knof if there is such a thing as "graduating" from mozzies. Seems like there is a lot of skill and experience in those fleets.

There are cons?

This is not the engineering of the sail, just my experience with it.

When I put the squaretop on the Tiger I expected to get better performance out of it in light winds. The first day racing it was miserable. I was sailing in bumpy conditions in light winds and finished at the back of the fleet. The next morning I looked at the leech, while on the beach. I noticed, sheeting and loosening the main, that there was a huge hook at the top while sheeted in. I marked the mainsheet where the hook stopped and raced that day with that slack in the sheet. I finish in the top three with the same conditions as the day before...much better.

So where do I think the squaretop shines? In windy conditions where you do not want to do too much sawing if you hold your own mainsheet. As Rick pointed out the top of the sail will depower on its own as a puff hits it. I usually play my own mainsheet and do not like to pump it in and out. Doing that too much, one handed, hurts the shoulder. The squaretop is perfect for this application.

Later,
Dan

Good post!

Higher sheeting loads. More area at the top to flip you forwards if running dead downwind in extreme conditions, or when transiting from beating to reaching to downwind.
There are some cons, but the pros outweight them massively in my opinion.

Dan,
That is what I teach for sail trim. Line up the points of mast base and sheeting center, trim so the sail is slightly off center of mast and mark the sheet. That way you know exactly where to sheet in after any maneuver, i.e., tack, start, mark rounding.
At least you are in the ballpark. In a puff, sheet in a bit more, in a lull, ease off a bit.

You certainly do not want to oversheet a square head, or any other sail for that matter.
Rick

Marchaj's book "Sail Performance" does a good job discussing head shape. The square head does have more area up higher, but b/c of the shape it's much more efficient (more equal loading along the chord length). I don't remember the percentage, but if you look at flow and usable area of a pin head, it looses something like 30% at the top.

I'll pull the book back out if I have time and find the section to reference.

Rick,
Does that spot always hold true or do you have to sheat more if you apply more downhaul creating more mast bend?

If the mast bend makes the blocks closer together (lowering the clew), then it will change. But, for most boats the downhaul does not significantly change the relativity of the sheeting blocks.
Rick

does this apply downwind too?

thanks guys for all the input. sounds like the squaretop is the winner, especially if the rig can become that little bit more "automatic". doe sthe extra sail up top not cause more healing moment due to the extra sail power "higher up the lever", i guess if it automatically twisits off and depowers itself it shouldnt cause too much drama, in 2o knots plus i guess i would be more inclined to run an older mainsail anyway.
thanks guys!!!!!!
p.s. dont stop with the info!!!!!!
its great to keep learning, even after racing for 30 years. you can always learn more

There was a huge string last year on this in SA with allsorts of technical stuff.
I remember asking Bill Roberts about it a very long time ago when the came back after all he was a rocket scientist at Pratt Whitney. It is not new but old technology that was re-born again in the late 70's early 80's or there about for beach cats.

He said some simple things to me:
A sail is a wing.
Ever see pointy wings on modern airplanes?
Also a bunch of scientific stuff about the way the wind leaves the sail, and the vortex of wind not going down the face of the sail.
Bill made fast boats and knows more about airplanes and rockets then me I took his word for it.
When I went flat head my boat sailed faster.

G'day Brian Big head sail is the way to go, Mitch Bayliss was here last weekend and he went like stink. I had a square top on my big rig Stingray though a lot smaller than the squares now. I found that to make the main hold it's shape I had to have tight main sheet but if I had the mast rotated properly it pulled the top of the mast over backwards and depowered the boat so I used less mast rotation. The 5.7's have gone from my square top to a F18 style, in light wind from what I've seen they seem to lay off quite a bit if you let any main tension off. Maybe super stiff top batten needed? Whats your new boat?
regards

Disagree.

When applying DH you are streaching the sail and bending the mast; this will change the sheet position.

THink about what is ahppening; mast bends and sail flattens (top of the sxail falls away); to get the sail back into a good foil, you have to pull more leach tension; this means more mainsheet.

When sailing without any extra DH, I have about 20cm between the blocks on my F16; when sailing with full DH (but needing to sheet in) my blocks will be almost block to block.

Brian - From a completely non technical point of view I'll say this:

In light airs/choppy water the square top seems slower, in flat seas it's about the same.

As the wind started to fill in a Victor (13kts) and we were able to stretch out on the wire the big head sail seemed to be faster, I sailed over the top of Brett and gained about 100m on Todd in one upwind work.

However - Todd did win the series with a pin head sail - it should be mentioned he is an excellent sailor with 15+ years experience on the boat (I hope he doesn't get a big head sail!)

I'm going to go out on a limb here and say that this is probably b/c it's much easier to oversheet a squarehead in light/med conditions than it is a pin head. Oversheeting is a painful death in light air.