flat top main

Discussion in 'Sailboats' started by whitepointer23, Jun 2, 2012.

  1. whitepointer23

    whitepointer23 Previous Member

    i have just purchased a used main sail which i need to get cut down, my sails have 9.5 meter luff this one is 10.5 meter luff. can i just get it chopped at the top and add a battern for a square top or are do square tops have a different cut to normal. the foot is okay it is just the luff that needs shortening. can i expect a performance increase with a square top.
  2. whitepointer23

    whitepointer23 Previous Member

    1 more question. how do gaff rigs perform compared to bermudan rigs, not very well i guess or we would all have gaffs. i would love to get some opinions on the merits of a gaff. i like the idea of a lower rig with a folding mast.
  3. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    Gaff rigs can be as effective as bermudan offwind, sometimes more so, but aren't nearly so good upwind.

    There's a lot more to sail design than just chopping the top off and putting a batten on: I'be be suprised if it works well. You also need to consider the rest of what's going on: a square top and a fixed backstay don't work well together for instance.

    If the whole rig, mast sail and everything works well together you will get a bit of a performance increase with a square top, depending on the precise nature of the rig. OTOH, if none of it matches well and all the components are fighting each other all you'll add is difficulty. Such rigs are complicated to tune and setup. Whilst I would probably have them on my racing dinghy if the mast were made to match the sail and vice versa, I'd think twice on a cruising boat, esp one put together on a budget from used components and various sources, because the advantages may well be out-weighed by disadvantages.
  4. Stumble
    Joined: Oct 2008
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    Stumble Senior Member


    Most racing boats are going to square top mains, but as Guest pointed out that is because the whole system is designed together. So the carbon masts they use are designed to fall off to leeward a bit when guests hit, opening the top and spilling air.

    Cutting a main down by just lopping off a section may work, but I doubt it will be very efficient. And unless the sail is a cross cut Dacron sail will likely destroy the integrity of the sail. Most modern sails (tri-radial and laminates) are built with the load paths being reinforced, those loads converge at the corners, cutting of the reinforcement will force sections of the sail not designed for the loads to take them. This will lead to massive failure very quickly.

    Even cross cut sails these days are somewhat designed for the loads, and cutting them down like you propose could be disasterous, but perhaps not as bad. My advice is to find a very good local sail maker and have them look at the sail you are contemplating, and get their recomendation.
  5. sean9c
    Joined: Jan 2011
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    sean9c Senior Member

    Also remember that with a big top main there is no backstay.
  6. whitepointer23

    whitepointer23 Previous Member

    thanks for the replys, i thought that might be the case. my boat has a very good rig now but i blew the main out in a blow and got this used 1 cheap. i will just get the sail; makers to cut it to size normally. pity though, i like the look of the square tops. i have twin back stays.
  7. luff tension
    Joined: Aug 2010
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    Location: auckland

    luff tension Junior Member

    Ive done a few cut-downs like that and they work just fine.
  8. whitepointer23

    whitepointer23 Previous Member

    thanks luff.
  9. Paul B

    Paul B Previous Member

    Please be careful about making decisions based on the opinions of internet denizens.

    You should consult your sailmaker and discuss the possibilities.

    If you think about it, cutting off the head would require you to rebuild the head, add the battens for the support, etc. You would probably have to change the luff curve to flatten the head a bit more, etc.

    Cutting the excess luff length from the bottom of the sail would require rebuilding the tack AND the clew, and would result in a shorter foot.

    Also, if the existing sail has reef points, cutting the sail off at the bottom is probably going to require rebuilding the reef points as well.

    I'm sure your sailmaker will have a professional opinion based on the construction of the sail. If it is a string sail neither option might be advisable. Best to wait on making a decision until after you sit with him/her.
  10. whitepointer23

    whitepointer23 Previous Member

    thanks paul, i will be getting a sailmaker to do the job , so they can decide to make it a square top or not.
  11. luckystrike
    Joined: Feb 2010
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    Location: Germany

    luckystrike Power Kraut

    I have done the same operation and it worked well. My sailmaker did a good job, adding two full length battens, one for stretching out the squaretop and one for stabilising the profile.
  12. Petros
    Joined: Oct 2007
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    Petros Senior Member

    A square top sail done properly by your sail maker should improve the performance noticeably. As much as the upper third of a convention pointy top sail does nothing but create drag and heeling moment, the flat top sail allows much more of the surface to generate thrust with less drag. There might be a slight raising of the center of effort, but with the other benefits will not likely create any problems for you.

    If you bought one at a good price I would certainly consider using it, just make sure your sail maker is familiar with how they are built so it can be altered properly. I would say you scored a good deal. Post pictures when you have it finished.

  13. whitepointer23

    whitepointer23 Previous Member

    1 more question. i was looking at the boat today and the new/old sail is about a meter too long. if i get it cut to a square top won't it catch on the backstays, and would the topping lift lay along the side of the sail not behind as it does now. are these things i should be concerned about or not. thanks again for all the great replys so far. p.s. this sail is a dacron racing main from an etchells, would it be too light to put reef points in.
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