canting mast 16ft Mosquito catamaran

Discussion in 'Multihulls' started by tasman sailor, Jun 1, 2011.

  1. tasman sailor
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    tasman sailor Junior Member

    Hello, i apologise for starting a new thread but here goes.

    The plan is for the manipulation of mosquito plans, as they are readily available, obviously this breaks the class rules, for a canting mast instigated by adjustable (controlled continuous line) side stays and a pivoting mast step.

    the purpose of the mast is to retain a vertical mast, perpendicular to water, while flying a hull, not to gain a component of lift from a sail like moths, and
    rs300s when they lean to windward. Also does the underwater profile of the hull when leant over, resemble an aerofoil and pull the boat to windward.

    Some questions:

    • How do i calculate loads on a sail does the force required to pull in a mainsheet differ from that to pull a must into the wind, how do i calculate this is it relevant through all points of sailing, is there a linear relationship between force required and windspeed?

      Is moving the sail through only one plane going to effect the weather helm? Windsurfers obviously use a universal joint and pivot through all planes for steerage and maybe counter something like this?

      How do you calculate the force on a stay or sail and appropriate pully ratios?

      Are the centre boards, being dual shaped like an aerofoil to pull the boat, minutely, to windward? Does this coupled with a curve offer a vertical component of lift on centreboards and hull?

      At what angle do A class cats and the likes turn out their hulls for efficiency while flying a hull, is the ideal angle for sailing a catamaran disregarding the sail (this will pivot and hopefully remain the same) directly relevant to this?

      Does anyone know of a manual winch geared continuously clockwise and anticlockwise or will a continuous self tacking jib setup attached to the stays work?

      Has anyone ever built a rotating hull setups, ive seen yours Doug Lord.

    thankyou for any and all responses
     
  2. Doug Lord
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    Doug Lord Flight Ready

    ====================
    You have? Just out of curiosity what do you know about it?
     
  3. bad dog
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    bad dog bad dog

    Mr Tasman - you ask a lot of questions! ;-)
    - that's coz there are a lot of mysteries with canting rigs. Allow me to fill in a few gaps from my experience with one on my old Catapult.

    How do i calculate loads on a sail does the force required to pull in a mainsheet differ from that to pull a must into the wind, how do i calculate this is it relevant through all points of sailing, is there a linear relationship between force required and windspeed?
    Others will no doubt give you the formulae, but I can tell you that the loads are high, and friction is the killer. A mainshheet-type system would make it easier, but that's a lot of weight in blocks and wet rope.
    A technique for avoiding this is to cant the rig to leeward just as you go into a tack or gybe. This works when you have time to set up for it, but in racing conditions this can be difficult.

    Is moving the sail through only one plane going to effect the weather helm? Windsurfers obviously use a universal joint and pivot through all planes for steerage and maybe counter something like this?
    In my experience, everything works better with the rig canted 5° to windward. Less weather helm, better pointing.

    How do you calculate the force on a stay or sail and appropriate pully ratios?
    ...Doug?

    Are the centre boards, being dual shaped like an aerofoil to pull the boat, minutely, to windward? Does this coupled with a curve offer a vertical component of lift on centreboards and hull?
    There may be a detailed answer to this, but I suspect if it's there it will be minute.

    At what angle do A class cats and the likes turn out their hulls for efficiency while flying a hull, is the ideal angle for sailing a catamaran disregarding the sail (this will pivot and hopefully remain the same) directly relevant to this?
    About 4~5°

    Does anyone know of a manual winch geared continuously clockwise and anticlockwise or will a continuous self tacking jib setup attached to the stays work?
    I looked and looked - and never found anything that weighed much less than I do! Well - 30kg-ish anyway. Way too much weight. But maybe you'll strike it lucky...

    [/QUOTE]

    Good luck - I love canting rigs! If my A needed more power or pointing I would definitely do it again!
     
  4. Doug Lord
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    Doug Lord Flight Ready

    Shroud and forestay loads can be calculated using Skenes or Larrson and Eliasson's "Princibles of Yacht Design".

    Mainsheet loads here(among other things)-see the "Mainsheet Load Calculator" : http://www.harken.com/blocks/blocks.php

    Sail Load calculator: http://www.sailingusa.info/cal_wind_load.htm

    Best(I've found) treatise on blocks and hardware:
    Chapter 14 p289-322 of "Sail Power" by Wallace Ross

    More info on setting sails correctly: "The Art and Science of Sails" by Tom Whidden
     
  5. bad dog
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    bad dog bad dog

    Skene's Elements of Yacht Design - what a classic, but written back in the 50s and then revised 60s?? - does not even consider apparent wind and the other dynamics a fast multi experiences - is it still ok to use for rig loads?
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ---------------
    Yes, for sure. Rigging loads should be sized based on the max righting moment(+safety factor)-apparent wind is not in the picture.
     
  7. bad dog
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    bad dog bad dog

    Yep I guess that's right Doug. Time i dusted off my copy! Such memories...

    Anyway, here's a pic of what Tasman is trying to achieve, as seen on a Catapult.
     

    Attached Files:

  8. Doug Lord
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    Doug Lord Flight Ready

    ---------------------
    Cool! Didn't see the Catapult reference... I wonder-are they close enough that Tasmans questions would be answered by the specs on the catapult?
     

  9. bad dog
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    bad dog bad dog

    Maybe - Catapult canting was not something you do easily in any breeze over 4kn.

    It used an 'endless' 6:1 on each stay, with one end crossing the boat over the tramp. The triple blocks were set so with mast vertical the distance block to block was about 600mm. Canted at 8° it was about 300mm on the windward side.

    In its original form, the forestay was fixed on a sliding bridle - when the rig canted, the block slid around the bridle so the load was always shared equally on each hull.

    I put a 16' skiff rig on it to see how the extra sail area and jib would work, and at the same time put a 3:1 adjustment on the forestay length, thus being able to rake the rig fore and aft at will, as well as canting. A bit of added complication for not much extra performance in terms of sail area. But the rake control on the water was great.

    It proved what Tasman said about windsurfers: in light air I had the rig right fwd and slightly canted, and this gave a great response. In 8~10kn I would move the rig right back and keep the canting at 5°. Then in over 12kn the canting could come over a bit further, max out at about 9°. Any more than that and it became counter-productive. Having it all controllable on the water meant I could sail all day in variable winds and not suffer from making the wrong settings on the beach.

    I tried it near 15° which gave insane acceleration in gusts but absolutely no unloading of the rig - as it became vertical as the boat heeled, it just powered up mnore, and then the angle of heel became so great I had reduced righting moment - and you can guess the rest.

    ps - the skiff rig: I don't get 'em. It was not really quicker than the cat rig, and much fiddlier and sensitive to mast set up etc. Mast had to be non-rotating - why do they do that??

    Attached is the sail plans I worked on back in about 2002 for the two rigs.
     

    Attached Files:

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