Aftmast rigs???

Discussion in 'Sailboats' started by jdardozzi, May 28, 2002.

  1. Fanie
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    Fanie Fanie

  2. Manie B
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    Manie B Senior Member

  3. Fanie
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    Fanie Fanie

    How come everyone have that link except me ?

    Are you guys hiding some things from me :D
     
  4. pbmaise
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    pbmaise Senior Member

    Dual Sails on aft-mounted mast designs

    Thanks so much for the article. It again helps substantiate my election to go with an aft-mounted mast. In the article I enjoyed reading:

    "As can be seen at closer AWA unconventional solutions are better than the standard sloop and in particular the two jib configuration with overlap seems to be able to produce higher driving force (at dynamic pressure =1) at the same heeling moment."

    I'm not so concerned about heeling moment with a 40 foot beam on my trimaran, however, this business of dual jib with overlap is keenly of interest.

    As you can see from my photos I have two crab claw sails made for the sea trials. One is designed for the 67ft mark and one for the 50ft mark. My intention if to eventually fly both at the same time. It will be so neat if a dual crab claw also proves to be a better solution like a dual jib.

    Now based on the book Sail Performance, C. A. Marchaj showing a crab claw is 190% more efficient, in combination with this new paper showing the aft mast design is better, and dual sail is better, I should start entering races.

    Again, thanks for your patience and understanding that I am conservatively proof testing rigging before raising the sails. I've invested quite a lot of money in the mast, rigging, and sails and don't want to make a mistake.

    Currently I estimate I'm about 4 to 6 weeks away from giving you feedback on the sail performance.

    Thanks Philip Maise
     
  5. Fanie
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    Fanie Fanie

    Philip, mistakes are always there it's just how large or small they are, so don't worry about it ! I'm sure the sails will work well. I think at this stage I'm more excited about it than you are :D

    What you will find is this sail setup has a lot less heeling force than probably most other sails. Can't you expedite your activities a bit ? I don't want to wait 4 to 6 weeks... :rolleyes: :D
     
  6. gggGuest
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    gggGuest ...

    Be prepared for a bitter disappointment because there are a lot of caveats to all that. Race boat rigs are not likee they are because of short sighted conservatism, no mattrer what some here will tell you, but because they work.
     
  7. peterAustralia
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    peterAustralia Senior Member

    To Fanie

    I was wondering if you had a summary of your trial with aft mast rig written up anywhere. Something that takes into all factors, like reefing, good points, cost, simplicity or otherwise, bad points, like how much does the C of E change when reefing etc etc,

    It is a long thread, 15 pages, to find a summary make take a long time.
     
  8. Fanie
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    Fanie Fanie

    Hello Peter,

    Reefing is very simple. I like fishing and the one advantage that stood out was when you get the big one on it is easy to put the sail away. You pull a rope and the sail is gone, you pull another and you're sailing.

    The center of sail does move foreward while reefing but has little effect since the sail area get smaller.

    Sail cost is per sq meter here, I just gave the sailmaker the sizes and got the sail back from him. In my case I had it modified three times for various reasons and testing. Like always on a small boat there is no space to do all you want and I plan to do more once I can get the other boat built *sigh*.

    Sailing with the sail is really simple, a novice can do that, pointing is good and the sail makes good lift with a lot less heeling than one would expect from the sail size. I was only once in wind I had trouble turning into the wind but that was because the tri is so small and all the weight aft. If the weight is moved foreward the problem went away.

    Tri's in general were always faster than cats, but I think with a sail on each hull could change this. Shorter standalone masts but with larger sail area and more leading edge.

    In a while there is going to be a lot of boats fitted with this sail. Fishing is not really associated with sailing but fuel prices and this sail makes a lot of sense.

    I would think on a hydrofoil thingy with this sail making lift could enhance staying up a bit.
     
  9. brian eiland
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    brian eiland Senior Member

    I didn't have that link,...first time I've seen that article.
     
  10. Fanie
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    Fanie Fanie

    In that case - Are you guys hiding things from US ? :D

    Brian, they're copying our sail...
     
  11. brian eiland
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    brian eiland Senior Member

    I dropped them a note via email. I was interested to see if they had knowledge of my somewhat extensive promotion of this mast aft subject matter, and if they had gone a step further with any analysis of the rigging involved. We will see what they say in response.

    It was strange that in their paper they never refer to an aft-mast or a mast-aft. I would have thought this term might have arisen, and some reference to it have been made....such as one reference to Procyon.

    It does appear the twin headsail arrangement with overlap was superior in most of their testing...just as I would have predicted.
     
  12. Fanie
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    Fanie Fanie

    Well, since a jib is ahead of the mainsail, calling it a jib is incorrect. Maybe we should come up with a sophisticated sounding name for it. Eiland rig sounds good to me ;)

    A twin or tripple overlap arangement should perform better yes. I once asked if one could make cuts along the stay to form multiple leading edges in the same sail - still believe it can be done - and I was told it probably won't work.

    Pls let me know if you get a response from them.
     
  13. MikeJohns
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    MikeJohns Senior Member

    The study is interesting but it's of limited usefulness IMHO.

    The sloop was never tested with an overlapping headsail this was an omission which could have had a significant impact.

    How would the sloop have performed in comparison with say a deck hugging code zero to match the deck hugging single sail of the aft mast config?

    In real life unfortunately such studies are not great recommendations. Ideal wind tunnel (and smooth water tank tests) produce data that is of debatable usefulness at times. Also that study is only for upwind sailing. There are no polars, not even for the various upwind conditions. For the VMG plots just one heading for figures 24 and 25. No error bars and I’d like to see the raw data scatter, for such relatively close results.

    20 degrees heel for 10 knots of wind is tender and questionable, and they apply Wolfson's VPP code refined for standard rigs to the aftmast without any verification. Anyone involved in VPP will know that it's essential to tie it to real data.

    Then there’s all the little inconveniences of the real world. For example there’s no consideration of the effect of wave resistance increase due to the change of longitudinal gyradius by concentrating the mass of the (heavier) mast and supporting structure in the end on the vessel. This alone would make it slower relative to the sloop for the ULDB configurations.

    Also I’d be concerned at sea that there is an inability to stack sail forward downwind, for good control, with other effects like smaller rudder angles. How do you fly a spinnaker safely ?

    Also consider that the bare rig is your final storm sail, and putting all that air drag aft will be a liability running in survival situations.

    For Ocean going monohulls I would have thought Procyon was a good example herself. [Edit] Relentless [Not Procyon] unfortunately was not am astounding success, and she was being just about given away recently after a long period on the market.
     
    Last edited: Oct 22, 2010
  14. RHough
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    RHough Retro Dude

    This is from 2004 ... 6 years ago. Anyone have NUMBERS yet?
     

  15. RHough
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    RHough Retro Dude

    This is from 2006 ...

    Has anyone addressed this?
     
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