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Old 06-29-2009, 10:09 PM   #1
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I have just seen the specs on the 2010 Lagoon 40 and it has square top main. Can anyone tell me what advantage you have by going this route other than additional sail area, and why would this be advantageous on a cruising catamaran.

I have seen Square tops on racing yachts, hobies and such, in those instances they have been used purely for speed. Could it be that you can have a shorter stick and still carry the same amount of sail without over sheeting.

From what I have read about them you have to reef earlier as not to have the top twist and they carry extra battens for support.

Unless I am missing something and that is very possible I am guessing that it may be a sales / marketing technique to attract novice buyers.
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Old 06-30-2009, 12:05 AM   #2
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If you mean the fully battened sails that are squared off at the top with a batten--many gaffers think of these as "modern" gaff rigs without the hassle. "Square top sails" are an extra sail that is carried on a topmast and it would be square. That's not what you're talking about

Actually, I though the reason on modern racers was to get more sail area up high. Its like the ultimate in roach. Doesn't mean the stick is shorter in that case. The traditional gaffers do have more sail area down low--thus your rig has lots of power but doesn't produce the same moment as a taller rig.

That's all I know--not much, eh?
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Old 06-30-2009, 01:52 AM   #3
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95m (1,000ft) main -- Stick something like 65ft off the top of the saloon, say 75ft off sea level.

Whereas most modern catamarans provide an increased fully battened Roach with a wide head board instead of a top batten - the leach in this one is a straight line with a batten that appears to be attached to the luff which then goes out at around 45 degrees to the peak in order form a small triangle along the head with small headboard. When the mainsheet is eased, what effect will that have on the small triangle?

Lagoon_40_Main.jpg

Apart from making an ugly boat more ugly (if that is possilble?) Guess it will provide more drive with the additional area higher up - time will tell, there are a lot of pre-owned Lagoons on the market.
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Old 06-30-2009, 09:23 AM   #4
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Geez that's an ugly boat...

benefits: more sail area for less stick height, could be good on normally undercanvassed cruising cats.

drawbacks: way more load on leech, and the batten cars (more tension on headboard cars, more compression on upper batten car.)

Very important to have a well-designed and built sail, and the best (and properly sized) mast track/batten receptacle/car system available.

Given the limited sailing performance of this type of multihull (heavy SA/displacement ratio, lower L/BWL chord ratio, the keels etc), the marketing/hype aspect of the 'square-top main' is perhaps greater than any actual performance benefits.

Having said that, the square-top main is very sexy, and I must have one too.
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Old 06-30-2009, 10:48 AM   #5
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Thank you Deva,

For the reference to lack of beauty !

What sailboat was in your post's picture ? It doesn't look like a Perry - Baltic 64.

Richard
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Old 07-01-2009, 04:59 PM   #6
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It's been so long since we've seen Deva - is that her? *You should tell people Deva's size to give people an idea of what size catamaran can cross oceans.

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Old 07-07-2009, 09:21 AM   #7
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Deva is a 38' modified Robin Chamberlin design (ex- "Kialani") built by OSTAC in 1992 in Brisbane. We left Mooloolaba in 1994, spent many years cruising SE Asia, Africa, and now she is lying in Brazil.

The main is original from 1992, the pic is from 2002. Heavy Dacron, well reinforced, by Ian ____ Sailmakers (he passed away)

Nice feature is the 8 full battens which are probably why the sail has lasted so long in decent profile shape. The battens seem to accept much of the dynamic load away from the sailcloth (maybe, or maybe I'm making it up) but the result is a sail that has lasted over 15 years in decent profile shape. The battens are tapered, so sort of force the sail into the proper shape.

The Ronstan batten cars keep eating up the 1/4" balls, which i suppose I need to change to Torlon instead, they must be under some serious load...

Back to square top mains... I believe they need to be built of composites rather than Dacron, to properly align the stretching load w the thread line of the material. I think Dacron's bias stretch is probably unacceptable for this type of sail design, further limiting its cruising utility over the long haul... and oh yeah, for sure you will break a lot of battens in that sail in the pic, if cruising...
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Old 07-09-2009, 08:41 PM   #8
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Honestly, you should have asked this in a beach cat forum. Go where the most knowledge is, and all that...

Square Tops (aka Fat Heads) do add sail area without making any other significant changes. However, that's not all they do.

The typical triangular shaped mainsail is nearly the worst aerodynamic shape possible. The top of the sail can't "capture" the air and make it flow back, so the air spills off in tip vortices and the suction draws air from further down the sail upward. This reduces the amount of lift created over a considerable portion of the top end of the sail.

The squared-off top increases the sails ability to "capture" this wind, greatly reducing these vortices and increasing the efficiency of the sail.

In light wind, the battens hold the leach out, making full use of the extra sail area. As the wind picks up, the top twists off, automatically opening the leach and de-powering the main.

Remember- most beach catamarans don't have reef points in their sails. They use downhaul and mast rotation to de-power first, then the traveler. If they still find they are over-powered they drop the spinnaker and/or furl their jib. Letting the mainsheet out is the last resort before survival techniques come in to play. (Loosening the main while the spinnaker is pulling will bend their masts.)

There are plenty of dacron square-tops. Most recreational catamarans come with these now. The racers use Mylar and Pentax and other exotics, just like they did with the old "pinhead" mainsails.

There doesn't seem to be any drawback to this shape for boats without a backstay to get in the way.
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