Main-less rig

Discussion in 'Multihulls' started by Spiv, Feb 10, 2008.

  1. Pericles
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    Pericles Senior Member

    For speedy mast lowering, the Norfolk Wherry took line honours.

    http://images.google.co.uk/images?q...GB:official&client=firefox-a&um=1&sa=N&tab=wi

    The mast is pivoted within a substantial tabernacle and is fitted witth a large counterbalance weight at the bottom. This enables the wherry to lower the mast for passing under bridges. The mast can be dropped, the wherry continues forward under its momentum and the mast is raised again on the far side by the crew of two. If there is no wind, or for manoeuvring, quant poles are used to push the wherry.

    http://www.horning.org.uk/stylegallery.php?page=wherry&menu=style4

    http://www.google.co.uk/search?q=no...s=org.mozilla:en-GB:official&client=firefox-a

    Hope this helps,

    Pericles
     
  2. Spiv
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    Spiv Ancient Mariner

    Malasai and Pericles,
    thank you for your input, always welcomed.
    I do not have a problem with lowering the mast, in another post I already had this picture, but I might just resubmit it. I could lower my 17.5m rotating carbon wing-mast in less than 2 minutes (electric winch....)
     

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  3. Fanie
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    Fanie Fanie

    Hello Stefano,

    I'm no expert on sailing stuff, but I can tell you what I know based on a little experience with my little tri to gain information on the aft mast setup.

    During me playing around with it I found the mast upright better than leaning foreward.

    With the mast upright you also get more sailing area and the aft stays are easier to implement.

    The loose end or clew should be extended past the mast - you don't sail with the sail in the centre of the boat, so the sail should be extended.

    The main sail can be extend any distance past the mast if support allows for it. Also makes it easier to keep the sail centre of force centre to the hulls as the sail centre of force moves foreward when you let the sail out.

    If you're looking to lower the mast foreward you can get away without an 'A' frame if you add side stays that swivel on the same horizontal level and in line with the single mast.

    The storm jib can be furled and tied to the mast untill needed. Will make the main sail easier to tack and using an auto tacking setup will have no hinderance form the storm jib's forestay.

    You can add battens to the main sail's leech to extend the leech area that is parallel with the forestay and you can still furl it.
     
  4. Spiv
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    Spiv Ancient Mariner

    Brian,
    I now had a chance to go through all those pages...I see that you have been considering the idea from all points of view.
    An inventor friend of mine had suggested to me the idea of pre-stressed curved masts, like in Procyon as they would provide the strongest, lightest structure possible. I was reserving to mention it later on.

    Reading Olaf's comments I understand the need to properly engineer the topmast.
    Your note on the torsional force is a little trickier to overcome, especially from the mizzen sail.
    I am giving up (for the moment) drawing by computer, the drawing shows a possible solution: a spar hanging from the fore and back stays. Could the mizzen sail and the headsail be attached to it?
    The main staysail could be attached to a cross member in the mast.
    Can that work?
     

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  5. Spiv
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    Spiv Ancient Mariner

    That is right, you cannot go and change the rake of an existing mast too much or you affecr the centre of the sail plan. In our case, we would design the sails and the position of the tip of the mast so as to have a balanced rig.

    Yes, that is how most peple lower their mast here, I had to attach stays to my daggerboards to achieve that.
     
  6. Triroo
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    Triroo Junior Member

    Attached are some photos of John Hitch's 52 ft Cat which sails exceptionally well without a mainsail. Paul
     

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  7. Pericles
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    Pericles Senior Member

    Triroo,

    Thank you for those photos. What more can you tell us about this vessel?

    Regards,

    Pericles
     
  8. yipster
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    yipster designer

    made some sketches a while back knowing the asymetric jib(s) have advantages, good to hear the John Hitch's 52 ft Cat sails exceptionally well
    than drew a double aerorig ended with a wingmast with endplate crowsnest and inflatable wingsail that perhaps better reefs vertically
    i can read that pencil drawing much better Stephano but i go for triangling even the boat
    from an RC site here A frame forges and some more good reading
     

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  9. brian eiland
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    brian eiland Senior Member

    Thats interesting Triroo...reminds me of another vessel I have mentioned somewhere on this forum.

    Can I suggest that you go back and 'edit' your posting and replace those huge size photo files to a smaller overall size. That would make it much easier for those folks with slower web connections to view the photos.....maybe edit copies of your originals down to 8.5 x 11 size and then replace those you posted with them. (I really noted the slow download time with this connection I presently using in Thailand)
     
  10. brian eiland
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    brian eiland Senior Member

    And as the mast gets lower to horizontal, it gets real ungainly to control using wires
     
  11. brian eiland
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    brian eiland Senior Member

    Hello Stenfano,
    It has been a couple of years since I last considered this 'wishbone mast' configuration in any detail, so I need to refresh my own mind as to what I was thinking when I made these drawings I posted here:
    http://www.boatdesign.net/forums/showpost.php?p=109336&postcount=34

    I do remember that in trying to take account of as many of the variables I saw, I determined that these were the three best possible configurations I came up with.

    I would not want to attach the mainstaysail forestay to a horizontal member as there just would be no way to maintain any tension in it. Likewise keep a tight forestay on the leading genoa sail would mean hi-loads in the 'backstay' that goes over the aft-jumper. That aft jumper pushes the mast forward at the same location as the staysail forestay attaches. This must be combated by the 'traditional' split-jumpers up forward of the mast. All of this 'activity' and attachments just seem to dictate that the mast be a single column at this point. Furthermore the wishbone legs were then shorter columns.

    With reference to the torsional load of the mizzen sail, I had thought this might be controlled with two lightly loaded lines from the outer tip of the aft jumper down to the beam sides of the aft deck.

    ..to be continued
     
  12. masalai
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    masalai masalai

    Gee Yipster, those land-sail guys really get down to the numerical analysis bit. Some impressive work there. Thanks, much appreciated...
     
  13. Triroo
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    Triroo Junior Member

    LOA 52ft, Beam 33ft, Mast 18mts above cabin, 2 genoas 100Sq mts each, 1 staysail 35sq mts, 2 x 50hp 4stroke outboard motors, 2 asymmetrical centre boards set a fair bit more forward than normal, 26 to 1 beam ratio over all. It was built in the upright position using the X beam as the main structure. The X beam divides the cat into 4 main cabins, galley & lounge foward, 2 double cabins, 1 port & 1 starboard, & nav station, head & shower aft. Maximum beam of the hulls is 2 ft, & they are double-ended. The hulls have no rocker at all, the bottom of the hulls are round & strip plank cedar up to the water line. The bottom of the hulls were built in one piece on the bench then jacked up & glued & glassed in place. The top sides are of Durakore and were also glued together in one long piece on the bench then lifted into place. The rest of the cat is built out of Durakore. Before the mast was fitted, 2 motors pushed it along at 13kts, 1 motor = 9kts. Top speed sailing so far, = 23kts, & has averaged 10kts for 24 hours. Points quite well & can go to windward in light airs using 2 genoas. Paul.
     
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  14. Pericles
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    Pericles Senior Member

    Thank you Paul,

    The third photo showing the two genoas set had me foxed until your explanation. Is the vessel sailing on a broad reach?

    Regards,

    Pericles
     

  15. deepsix
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    deepsix Senior Member

    1 person likes this.
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