Square top mains?

Discussion in 'Sailboats' started by kenwstr, Dec 6, 2005.

  1. Perm Stress
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    Perm Stress Senior Member

    My considerations were actually for the same boat with same spars, but different mainsails -square top and conventional one.
    For this dilemma I would like to hear well based opinions.
    :)
     
  2. michael pierzga
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    michael pierzga Senior Member

    Then you are asking if the bigger square top mainsail will perform to its Rating ?
     
  3. Perm Stress
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    Perm Stress Senior Member

    No, just in absolute terms.
    Modern rating systems like ORC I consider fair enough not to bother about if a boat is not strictly racing oriented.
     
  4. michael pierzga
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    michael pierzga Senior Member

    Then I would say a block head main will be faster. More sail area always wins.
     
  5. themanshed
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    themanshed Senior Member

    I tested two sail on the same boat and saw a difference. First the sail was a pin head, and then modified to a flat head. Same boat – Same skipper. The only difference was the head of the sail (it was actually over stitched on the pinhead) and a small batten. On subsequent sails I had the flat head sail made directly. The boat was a light 5.7 meter multihull I noticed an overall performance.
     
  6. michael pierzga
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    michael pierzga Senior Member

    As an observation.

    Ive been sailing a fat head ,fully battened main, for 20 years. about 300,000 miles. The boat is a masthead sloop. When hard Upwind I cant trim the top of the main...get the batten near centre line, without over triming the rest of the main. On a close reach its powerful and fast. Block head mains belong on fractional rigs.
    .
    The reason for the fat head is that a standard pointed head mainsails luff length proved to be too long to furl inside a prototype hydrualic in boom furler. We shortend the main hoist by 1 meter and 40 to get the sail into the boom. To compensate for the lost luff, we put a big fat head on the main. The top batten kisses the backstay . The boat is 80 ft.
     
  7. gggGuest
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    gggGuest ...

    It doesn't work like that. If you have too much area in the head for the stiffness of the topmast then the sail will just twist off and dump power early no matter what you do with vangs or cut or or trim anything else. Well, not unless you put jumper struts and wires or whatever and support the mast externally anyway.
     
  8. Perm Stress
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    Perm Stress Senior Member

    Could you be more specific?
    As all those effects described depend on "how much" rather than on "unconditionally, in principle".
    On what boat you did you experience effects just described?
    Not that I do not believe in your statements, I'm just hungry for more detailed description on what did happened and how. :)
     
  9. Mikko Brummer
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    Mikko Brummer Senior Member

    Like in the case of the JPK the mast maker Eric Duchemin had to add 11 kg to the square top mast, to make it stand up for the extra loads. Even if the mast was 30 cm shorter. Not all of it was carbon fibre, though, there was double backstays and and the upper shrouds were re-dimensioned.

    "Il y a 11 kilos de moins dans le gréement de la deuxième version, non seulement parce que le profil est moins dimensionné en unidirectionnel de carbone – puisqu’il n’y a plus de corne, donc moins de compression des lattes et surtout un pataras unique –, mais aussi parce que nous avons pu diminuer la section du haubanage. Dans la version à corne, il faut que le profil tienne lorsqu’il n’y a plus de bastaques. La section du profil est la même, avec 30 cm de plus et une potence renforcée en carbone de 35 cm en tête de mât pour permettre de passer un peu de rond de chute sur la grand-voile."
     
  10. CT 249
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    CT 249 Senior Member

    Yep, on a multi like that you'd no doubt see a performance improvement. When the Tornado rules allowed them to use squaretops, old mains were modified like yours and there was an improvement.

    However, whether that shows that squaretops are "better" is another matter. For one, any increase in sail area will make the typical cat go quicker a lot of the time, all else being equal, so the fact that some boats go better when you add sail in the form of a squaretop is not really evidence that squaretops are "better" IMHO. UNless you did the test, you wouldn't know whether you could have gained even more speed by adding the sail area by going for a taller mast without a squaretop, could you?

    And what some of us are pointing out is that in many craft, adding a squaretop that works is not that easy. If you add a squaretop to a "normal" mast (not a big one as seen in most production cats) then it can just bend too much no matter what you do with the vang and sheet. And in light winds when the mast straightens, sometimes you can get so much depth in the squaretop (or rounded fathead) that the leach stalls, no matter what you do.

    So you end up needing modification or replacement of the spar and many other pieces of gear. You can also, in my limited experience, get further issues such as extremely high mainsheet loads, which is something that people like me hate - I want to be able to tweak without grunting or winding a winch in its lowest gear. And even when we stop sailing, there's the issues that Mikko talked about, such as having to get the top battens out to pack the sail away on a moored boat.

    I spent the winter doing shorthanded offshore races on a tri with a screecher, masthead and non masthead assys, twin backs, genoa, big head etc. All that gear did make the boat fast, but on the 20 mile races I'm sure we actually spent more time on the boat, packing away all that gear, than the slower monos with their simple mains and non-overlapping headsails. The time we saved on the course was compensated by extra time getting rigged and unrigged, and personally I'd rather be sailing than packing.

    It was a classic case where adding speed made the overall sailing experience (IMHO) less enjoyable and looking at the boats that people actually buy and sail shows that most sailors think the same way. Squaretops could be similar in some ways.

    And still, we are doing all this to try to make something that is LESS efficient (when heeling moment is a limit) than a sail with a narrower head, according to very well developed aerodynamic theories used by people (among others) as those involved in the America's Cup wing design.

    So sure, there's no doubt that the squaretop works in terms of making particular boats go faster, but what I think some of us are saying is that it doesn't make all boats go faster, it may not be faster than just using a taller rig, and it DOES come complete with hassles that may not make it as much of an advance FOR ALL OR MOST BOATS as some of the hype says.
     
  11. CatBuilder

    CatBuilder Previous Member

    I've never had a square top, so I do not understand this.

    Isn't there a car for the top batten?

    Why do you need to take the top batten out? Can't it just drop down into a stack pack or something?

    [​IMG]

    I was looking at doing a square top on my boat to add a little extra sail area and just for fashion (charter boat). So... why would the stowing of the sail be any more difficult? I'm not following that.
     
  12. michael pierzga
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    michael pierzga Senior Member

    Well...the more batten cars the taller the stack. On cats a big head main makes sense because you are not windward machines.

    Have a good look at Volvo race boat mainsail ..."Lazy Jack "....leech control systems. If I see a good photo I will post
     
  13. CatBuilder

    CatBuilder Previous Member

    Cats are not windward machines? You must not be seeing anything more than Lagoons and other slouches (with keels instead of dagger boards - remember that thread?) where you are located.

    Performance catamarans spend the vast majority of their time sailing close to the wind, even if a nearby mono is on a reach.

    Why? Because as your boat speed increases the apparent wind moves forward.

    Cats (good ones) spend a very large portion of their time with the apparent wind forward of the beam.
     
  14. michael pierzga
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    michael pierzga Senior Member

    Ill take your word for it...Ive never met a cat that was particularly weatherly.

    My experience with fat head mains are that they really shine when close reaching.
     

  15. Paul B

    Paul B Previous Member

    That says more about the trimmer than the sail.

    There are thousands of fat head mains that trim just fine, and thousands of people who know how to trim them.
     
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