Single-handed Skiff

Discussion in 'Sailboats' started by nacra5.8, Jun 17, 2012.

  1. Doug Lord
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    Doug Lord Flight Ready

    It seems to me that a narrower boat designed from scratch to use a rudder t-foil may be a good combination for your conditions. Some of the problems associated with the narrow shape may be overcome by the lift from the foil-allowing both quick planing and reduced wave drag. Foil lift upwind and the foil pulling down downwind may really allow a narrow shape to come into its own.
     
  2. nacra5.8
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    nacra5.8 Junior Member

    Alright, thanks GGGguest. I might try starting over with the design, and going to a 12 or 13 foot boat that's a fair bit wider. I was definitely thinking along the same lines as your thoughts on beam vs. length, but I kept coming back to the Plus Plus website where he mentioned that he wished he would have gone longer and shorter. I think I needed to start the design over anyway to be able to extrude the deck correctly, I messed that up on this one. Rocker-wise, I would lean towards a middle-of-the-pack kind of boat, but with a T-Foil rudder for downwind, do you think it would be OK to go with a 'low rocker wedge'? I'll have to dig up some pics of the Aussie 14s, I haven't seen many.

    Plus Plus Site:
    http://www.devboats.co.uk/plusplus/hulldes.htm
     
  3. nacra5.8
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    nacra5.8 Junior Member

    Sorry Doug, I just missed your post last time. I hink I'll try that, a shorter and fatter boat than what I was planning, but with the T-Foil taken into account, still skinnier than my earliest 12 foot long design (which I haven't uploaded here yet)
     
  4. gggGuest
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    gggGuest ...

    Mmm, but that was intended as an all round boat primarily for inland waters. I'm not unaquainted with the design for that one.

    In your place I don't know that I'd stray very far from the sort of length and beam of successful boats that have sold in numbers like the Contender, Musto Skiff, RS600 etc. The IC is longer and thinner than those, has blistering upwind pace but is less dramatic downhill. You can already do that with a multihull... Certainly not much below 14'6 or 15' waterline unless you have a specific desire for a short boat with resulting advantages and disadvantages.

    I don't have good expeience of the design tradeoffs and influence the T foil brings.
     
  5. nacra5.8
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    nacra5.8 Junior Member

    Alright, I'll try stretching the design to 14' 6"
     
  6. nacra5.8
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    nacra5.8 Junior Member

    On another note, what's a good wing angle (ie compared to parallel to the water). 15, 20 degrees?
     
  7. nacra5.8
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    nacra5.8 Junior Member

    Here's some pics of the new 14' 6" / 15' skiff- I went pretty wide, squared off chines, not too much flare ( I had a bit more earlier), I think the bottom might be a bit flat right not, it's hard to tell from the angle DELFTship gives you.
     

    Attached Files:

  8. nacra5.8
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    nacra5.8 Junior Member

    Also guys, using Bethwaite's Sail carry power / weight ratio, I'm leaning towards going to a cut down main/jib setup, versus only a main. With a main, the ration would be around 0.28 (28%). If I shorten the main and jib to around 150 square feet- and now the ratio is 0.35 (35%) slightly above the 0.30 minimum needed for windward planing. I also plan on cutting around a foot (or more?) of off the daggerboard, I won't need it especially in the higher winds where I sail.
     
  9. Doug Lord
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    Doug Lord Flight Ready

    ====================
    When you say shorten the main and jib are you talking about cutting down an I-14 rig as opposed to having new sails made?
     
  10. nacra5.8
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    nacra5.8 Junior Member

    Yes, but also I completely messed up the calculations- I divided by a 17 instead of an 11. Here are m revised calculations, which would lead me to stick with the main only rig:
    Full-size I14 main only: from 0.36-0.43, depending on how much I cut off the daggerboard, and the final weight (150-180 pounds). Within windward planing range
    Cut down I14 rig (main and jib): 0.45-0.5 (higher, but also would make the boat more complicated...)
    And, for shits and giggles, a singlehanded boat with full-size I14 rig and 20-foot wide racks:0.55-0.59
     
  11. nacra5.8
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    nacra5.8 Junior Member

    Normal I14 is around 0.35
     
  12. Doug Lord
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    Doug Lord Flight Ready

    Just out of curiosity, what's your designed max RM and the distance from the CE to CLR? This is interesting and got me thinking about how much weight I'd have to add to the "wing" of my boat to achieve an SCP/total weight ratio of .31-about 62lb. Not bad for a future turbo -up....
    -----
    I'm not sure cutting down sails is such a good idea unless looked at real carefully by a sailmaker. Good Luck!
     
  13. nacra5.8
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    nacra5.8 Junior Member

    Alright Doug. I reverse-calculated the I14 ration of 0.35 to get an average number for them of about 11 feet. In High Performance Sailing, bethwaite says that Aussie 18's were around 12+, but I think that both sails and foils have gotten higher-aspect since then. I was using 10 feet for main-only, and 8.5 for main + jib. Cutting-down wise, if I only take sail off of the bottom, I think I should be OK, right? i would cut off of the bottom of the mast too, to keep the luff curve matched up. Max RM is (180 x 8) for average person, then 9 feet beam / 2, plus around 6 inches (for heel), plus 3 feet for center of mass.
     
  14. nacra5.8
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    nacra5.8 Junior Member

    which is 1440 ft/lbs
     

  15. Doug Lord
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    Doug Lord Flight Ready

    ---------------------
    N5.8, My boat is 14.6' with a relatively low aspect square topped main and a relatively high aspect jib, 120 sq.ft. total and the CE-CLR is 11.5' . You should probably lay your sail plan out to scale and see how it turns out. I set the CLR at 34% of the board span under the boat to take into consideration the small lateral resistance from the hull.
     
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