Square top mains?

Without knowing how the rigs compare in area, mast height, etc it's difficult to impossible to state how much the difference sail shape by itself makes in performance. If the square top rig is faster because the sail area is larger than how would it compare to a different shape with the same area? If it is faster because the area is distributed higher with an associated increase in heeling moment than how would it compare to a different shape with a taller mast but same heeling moment? Or is a square top rig with the same heeling moment and area faster?

 

The JPKs had the same sail area, but the normal mast was 35 cm taller. They also had similar righting moments (measured), as I recall the normal rig boat had 30 kg removed from the bulb to compensate for its 11 kg lighter rig. Both had North 3DL sails and I know that North did a big effort in optimising the square top sail, to get it right.

 

Than with same masts and bulbs, who would be the winner?
Just your opinion.

 

Then you could no longer have boat on boat testing. One boat would have more sail area. The original test sounds logical.

 

I do not say or think the test is not logical.
I am just curious about the point in question.

 

Right on all those points, AFAIK. I wasn't trying to say that your posts were wrong about anything.

All I was disputing was the claim (by another poster) that two boat testing worked better in cats than in monos.

 

Interesting figures. If you are adding 11kg of rig + 30kg of lead with a squaretop one imagines you are also adding quite a significant bit of cost as well.

 

The trouble is to a large extent these comparisons are always flawed, because there are so many interacting factors.
Should you compare rigs with identical sail area, or identical span, or heeling moment, or cost or identical weight or what? All these are equally valid factors to test different concepts against, but you can't test all of them without an enormous study, and in any case the smart money says that the results you will get out at the end will say "it depends". It may not depend on very much if one idea has many advantages, but most likely there will be one use or set of circumstances in which the other will have its points.

 

Fashion statement, yes, I totally agree.

 

Not to mention full length battens, batten fittings & luff track systems, double running backstays on winches, plus a system to enable to stove the squaretop inside a boomcover: the head needs to be released from the mast to swing to diagonal batten along the boom.

 

With the same mast height, the square top is more efficient, yes, even if the sails were the same area (triangular sail with a longer boom). But the point of the triangular sail is that since it is heeling the boat less, you can make a longer mast and likely end up with a better boat than the one with the square top.

 

Thank you for explanations.
Shorter boom for the same sail area is quite inviting in many cases. .
_______

Than, if our constants are the same mast and boom instead of sail area, (and assuming the backstay is not here at all) the square top would be at clear advantage -more area and more efficiency at the same time.
I think so.

 

Well that depends whether extra area and even greater in proportion heeling moment is a good thing where you sail.

Don't forget to you are going to want a *much* more powerful kicking strap/vang/whatever you call it where you are, the boom will thus need to be stronger and the space and engineering will need to be there for the kicker too... Then the mast for the square top needs a stiffer top mast and a whole lot of other factors come marching in.

Don't get me wrong, I had what would now be called a moderate square top main for a boat I built back in 1998, and I'll probably have one on my next boat, but there are always tradeoffs in these design decisions...

 

Well, if we talk "normal" boats, not racing machines optimised for the very last gram of weight, all this additional strength and stiffness may well be already here in existing safety factors.

Or just account will need to be taken for softer topmast when making the sail and trimming it.

Stronger vang is actually not that difficult to create. I did it many times on boats I did skipper by simply adding a cascade to existing 1:6 or 1:4 purchase. (Many boats in my area have strange habit to have a vang not stronger as the mainsheet )

 

Windsurfers seem to do all right with square tops, bendy masts, no vangs (wishbone) and deliberately loose leeches. On a displacement long board a pinhead sail might in some conditions out perform a square top. but I doubt you will see them used any time soon on modern planing boards. I don't think testing two identical boats with different sails is a valid test except for the boat tested. Different horses for different courses.