High performance Gaff sails?

Discussion in 'Sailboats' started by BenMP, Mar 18, 2011.

  1. BenMP
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    BenMP Junior Member

    I have noticed that many of the newer high performance sailboats have a main similalr to this:
    [​IMG]
    or these:
    [​IMG]

    Where does the Bermuda rig leave off and the gaff rig begin?

    I was wondering if the newer Bermuda sails are using battens or a very large headboard to hold the roach out, wouldn't a carfully designed gaff rig give equal or better performance (added controls etc.)?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    You've hit the nail on the head-there is lots of room here for improvement. I've built an RC model using a curved pivoting gaff as well one with a straight gaff. The "peak" also had an adjustable outhaul and the "throat" was a little adjustable. On the model, the main benefit was allowing a more rectangular planform without requiring full battens. I think there is lots of room for experimental gaffs and other ideas that can allow the upper part of the sail to be controlled(via an upper outhaul) like the lower part is. These rigs also allow automatic gust response. In model racing, with boats of similar sail area, the "gaff" boats were always lots quicker upwind and a little quicker downwind.
    I think square top jibs with an upper outhaul could also be beneficial-even if only adjusted before you go out.
    Lots of room for development......

    Pictures: left to right-the first and third pictures show rc models with two different kinds of "modern gaffs" both with upper outhaul. The middle boat shows an experimental boat I designed and built about 1975 with an upper gaff that also served as masthead floatation-no upper diagonal batten and an adjustable outhaul controllable from the cockpit. The fourth picture is the rig for my 16' foiler with a square top jib with the head supported by a short gaff. The halyard was attached to the gaff about 25-30% aft. The second to last picture is a model rig with gaff supported main and jib giving both sails a more rectangular planform with adjustable upper outhauls. And the last picture is a mini with square top jib using a diagonal batten-not as good as the gaff version, in my opinion.
    Click on image:
     

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  3. Boston

    Boston Previous Member

    I think one characteristic of a gaff rig was at least to keep the center of effort low and another characteristic was to spill wind as a boat heels over past its point of efficiency. I seem to remember something about the length of the gaff and its angle being a huge factor is what makes a friendship sloop such a seaworthy little boat.

    so the type of gaff ( if its a gaff at all ) being employed on these yachts is a whole different animal than the more traditional ones
     
  4. TeddyDiver
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    TeddyDiver Gollywobbler

    Some of those sails are kind of gaff sails allready.. anyway I wouldn't call them bermudan anymore.. IMHO
     
  5. JRD
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    JRD Senior Member

    In that case I have a gaff rig too! Excuse the reef, its normally to the masthead, photos taken during initial rig set up. The sailmaker actually refered to the top batten as a "gaff batten" so there you are. The batten is very stiff carbon tube with a flexible section at the luff. I havent examined the photos of Dougs various masthead systems in detail but some appear as if they have mechanical control of tension or rotation (I might have this wrong). The only controls here are vang and cunningham, very conventional. Haul on the cunningham, and the top opens in gusts without the leech twist to de-power. Keep the leech tight and it points.

    I bet the real sailors 70-80 years ago would have loved a nice light carbon fibre gaff instead of the heavy wooden gaff thrashing around during each tack, gybe and gust.

    Cheers
    Jeff
     

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  6. FAST FRED
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    FAST FRED Senior Member

    Look at any 100 year old Dutch boat mainsail.

    They had the right concept then.

    FF
     
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  7. Doug Lord
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    Doug Lord Flight Ready

    High Performance Gaff

    ==========
    You've got it right, Jeff: the "gaffs" I showed (including on the full size jib on my boat) all have adjustable upper outhauls.
     
  8. BenMP
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    BenMP Junior Member

    Interesting. Thanks for the information.

    How do these sail compare to a comparable Bermuda style rig on the same boat?
     
  9. Doug Lord
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    Doug Lord Flight Ready

    High Performance Gaff

    ================
    Squarehead sails with diagonal battens are faster than triangular sails of the same area. The "high performance gaffs" I showed are faster compared to another model with a triangular sail of the same area-proved in extensive testing-but haven't been used enough on full size to really compare. The fact that they are similar to square heads with diagonal battens but with more sail control features would tend to make me think they are fast.
     
  10. Milan
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    Milan Senior Member

    Yes, pretty close. Probably the best windward, (short handed), sail possible with traditional materials.
     

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  11. BenMP
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    BenMP Junior Member

    I can't help but notice that the new "gaff" sails look similar to a Chinese Lug sail (only not a lug rig at all) could you use the battens of these for reefing (with lazy jacks) like the Chinese sail?

    Also, how do the curved gaffs of the Dutch boats work? Is there an advantage over the straighter ones?
     
  12. JRD
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    JRD Senior Member

    Look at the way the Vendee Globe or Volvo 60' racers are using slab reefs. Not using the battens for reefing as such, they just use reefing points. The full length batten just help to hold the sail in the correct shape once the reef is in place.
     
  13. PAR
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    PAR Yacht Designer/Builder

    Lets not call these new square heads a gaff folks, there's huge differences between them. The gaff rig stopped development, for all practical purposes about 80 years ago. Had it continued, the three most important features to receive further exploitation, would be gaff dimensions, weight aloft and windage.

    Carbon fiber and spectra would solve the dimensions and weight issues for the gaff, so windage issues would next be addressed with internal halyards and lifts. This still leaves the mast shadow, head twist off, mast/sail attachment, boom control, weight aloft, etc. as other concerns. to contend with.

    Sail tracks strong enough to accept the torque of the gaff, internal outhaul sheaves and lines, boom vangs, gaff vangs, more carbon fiber and spectra stuff address some of this. Maybe fully rotating masts, full battens and shaped sock luffs can deal with the other issues, but it's still just fodder in terms of the gaff rig.

    Some hermaphrodites have been produced, but most can be categorized in the Bermudian column. As a rule, high aspect gaff rigs don't stand well and when you engineer them to do so, they become fat headboard Bermudians for the most part.
     
  14. BenMP
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    BenMP Junior Member

    PAR,
    I'm still not real clear on what the difference is between a "bremuda" sail with a gaff batten and a "gaff" sail with an external gaff. Could you explain some of the (perhaps not so) subtle differences between the two?

    Sorry for the repetition as you know I'm a bit slow on the uptake sometimes.
     

  15. Milan
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    Milan Senior Member

    Of course there is a huge difference and traditional gaff can’t come near the performance level of the square headed Bermudian rigs, that take full advantage of all modern aerodynamic knowledge and new, light, strong, dimensionally stable, (and very expensive) materials.

    Still, I find it fascinating how traditional, intuitive, empirical engineering in some cases reached very high efficiency . (Especially when you consider limitations of materials that were available at the time, and how simple and cheap these rigs were).

    Loose footed, Dutch style short gaff rig, is a very good example.

    Short gaff considerably improved all three named features – gaff is short and tin, so it is a very light. Mast is in one peace, has a lot less windage then gaff with top mast and top sail. Twist is also much less of a problem with a short gaff. Loose foot gives a good shape to the sail from top to the bottom. Mast shadow turbulence that spoils flow of the air on the luff is lessened by keeping distance. Sail is laced to the mast in such a way that there is a considerable gap between the mast and luff of the sail. Therefore, luff works in a clean air.
     

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