Aftmast rigs???

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

  1. FAST FRED
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    FAST FRED Senior Member

    Folks that want a sail that will happily short tack , and also overlap the mast can simply copy what the Dutch have been doing for centuries.

    A conventional jib has a rope loop added to its foot,where the traveler would be with a boom ankle buster.

    A rope is lashed side to side threaded in the loop.

    When tacking the jib sheet is cast off and when the boat tacks, the LUFF works to keep the boat moving .

    The leech is not tailed as its a waste of effort short tacking up a river .

    Might be a useful mod to any jib for a short handed sailor.

    This was done on heavy commercial vessels that would carry their way thru the tack..
     
  2. brian eiland
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    brian eiland Senior Member

    Don't use the Main?

    ....over on this other forum there has been a discussion entitled 'Don't Use the Main'...sail, that is.
    http://www.cruisersforum.com/forums/f48/dont-use-the-main-115978.html

    I wrote a few postings in response, including this one just recently:
    Perhaps we need to take another 'tack' at the reasoning here.

    The subject thread is titled 'Don't Use the Main'sail... that is. The problem with that solution is it doesn't take into account the interdependence of the headsail and the mainsail. A headsail can be a more effective sail than the mainsail, BUT it can only do so with the HELP of the mainsail.

    Lets go back to this link at well respected WB-sails,
    http://cdn2.hubspot.net/hub/209338/news/Ad_aerodynamics/index2.htm
    and look at the text in the middle of the sail.
    MenuBoat, WB sails.jpg
    Then have a look at this flow illustration from that same website. Which sail has the greatest pressure differential across it, and which one has that differential more in line with the direction of the boat's travel,...obliviously the headsail
    AirInSlot, WB sails.jpg

    The sailboats illustrated here are fractional rigged boats, much like most of our catamarans are rigged,....our headsails are much smaller than the mainsails. So if we reduce the size of the mainsails (by making them roller furling, or eliminating their roach, or eliminating their fat-heads, etc, we are going to significantly cut the boat's performance, because we don't have headsails large enough to make up the difference !! We have potentials to make the rigs more effective by increasing the size of the sails that we can make more effective, but we continue down the path of making the following sail (the mainsail) ever bigger and the headsail ever smaller.

    It's this reasoning that lead me to the twin headsail rig on my mast-aft configuration. I wanted a nice big headsail that could be helped by its following sail (my mainstaysail). And I wanted it to occur in a more 'parallel manor' than the traditional configuration (a more consistent slot).

    Here are a few illustrations (rough draft) that I made of 3 style rigs, fractional jib, masthead jib, and then aft-mast rig.
    Note that the horizontal lines in each of the illustrations represent the centerline of the vessel when viewed from above, so you see the overlap of each of the two sails at each elevation in the rig.
    Fractional & Masthead Rig slots.jpg


    Look how consistent that slot is for the aft-mast configuration.
    Aftmast Sail Slots2.jpg
     
  3. brian eiland
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    brian eiland Senior Member

    Interesting Rig Solutions (aft rig and use of wishbone boom)

    Moving the mast aft, and more concentration on headsails (not quite to the extent of mine ;) ). Interesting boom(s) arrangement also.
    Look at either of these links, and click on 'Rig and Sails'

    http://www.freeflowcatamarans.com/FF52.aspx

    http://www.freeflowcatamarans.com/FF66.aspx

    I received this note from Nathan....
     
  4. brian eiland
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    brian eiland Senior Member

    Pointing Ability of a Twin Headsail arrangement

    Just happened across this posting on another boating forum

    http://www.cruisersforum.com/forums/f48/has-any-one-sailed-or-seen-a-cat-with-two-roller-furlings-16935.html#post179430

     
    Last edited: Jun 28, 2015
  5. Jamie Kennedy
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    Jamie Kennedy Senior Member

    Interesting boat, Zenataos. You can see the interesting rigging in this picture here as she is, literally, flying through the jungle !!! ;-)

    [​IMG]
     
  6. brian eiland
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    brian eiland Senior Member

    And now the new Lagoon 39 moves its mast aft as well.
    lagoon_39_sailing2_2015.jpg
    lagoon_39_starboardside_2015.jpg
    lagoon_39_birdseyeview_2015.jpg
     
  7. DennisRB
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    DennisRB Senior Member

    Zenataos now has a regular bridgedeck cabin instead of the poles, it also now has a aft mast setup with no main similar to what Brian promotes. Apparently it does not sail well anymore with this setup. But it was made with used sails etc and looks a little under canvassed so has room for improvement.
     
  8. brian eiland
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    brian eiland Senior Member

    Any photos of modified boat.
    Brian
     
  9. DennisRB
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    DennisRB Senior Member

    I will try to get some
     
  10. brian eiland
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    brian eiland Senior Member

    Victor Tchetchet's Rig

    I mentioned this name 'Victor Tchetchet' on my website as one of factors (a minor one) that resulted in my pursuing the mast-aft idea many years ago. But somehow I never did post a photo of his rig. That's likely because I started this quest long before I became computer literate, and didn't have a digital photo at the time. I just today went looking for a photo or illustration of his rig, and was surprised when I could not find it anywhere on the internet.

    So I dug back thru an old external hard drive I had and found a photo and an illustration from that era. I thought they should be added to this subject thread for historic purposes.
     

    Attached Files:

  11. DennisRB
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    DennisRB Senior Member

    Zenataos (Wired) now aft mast.
     

    Attached Files:

  12. brian eiland
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    brian eiland Senior Member

    This is NOT a rig from which I would expect any decent windward performance.

    And to tell the truth I don't really understand some portions of the rigging.
    1) What purpose does that small aft spreader at the lower forestay attachment point serve? Its not helping with any sideways forces exerted by the lower forestay, nor resisting any forward forces exerted by that forestay??

    2) The upper and lower backstays are just to 'shallow' of an angle to allow for any tension in the forestays.

    3) I would be concerned that any good size wind gust into that unfurled leading headsail could bend over the top portion of that mast (seriously out of column),...and depending on how the upper backstays are attached it could thrown a big twisting force into that upper portion of the mast.

    ...appears to be a rig to deploy two lateen type sails void of their normal supporting long spars.

    PS: Even this somewhat similar rig looks to be better done
    Bamba 50 http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-33.html#post533098
     
  13. Kojii
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    Kojii All is remodelling

    Is this a candidate for a bipod?

    Most of Brian's concerns are related to the extruded aluminum pole weaknesses. They are given to bending in all the wrong ways with poor (finite) modulus aspects ( i can hear the aluminum apologists winding up their defenses now). Many people forget they were originally called "bendy masts", like it was a sales point, and they fold routinely, are prone to corrosion (in hidden places), and are very difficult to tension properly for the recreational boater.
    I admire the willingness to step outside the box, but there is a reason people stay inside the box - it is well-charted territory. Bipod could be less expensive than the replacement aluminum you may end up buying when this tube collapses. Just my thoughts, FWIW.
     
  14. sharpii2
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    sharpii2 Senior Member

    It should be pointed out that this other boat is much heavier, maybe twice as heavy as the boat in question.
     

  15. brian eiland
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    brian eiland Senior Member

    I suspect you meant to say a channel that was 2 boat lengths wide. ??



    Sorry I don't understand what you are saying here. That jumper strut might lend some small amount of force to keep the mast in column, but I don't see it adding any appreciable load carrying force to the upper forestay.
    Are there 2 lower (aft) shrouds, and 2 lower backstays, all from that 'hounds area' where the inner forestay and jumper strut are located??


    Perhaps I need to clarify what I am saying here. In the first place many people just assume the the forestays on our vessels are exerting a big force pulling the tip of the mast forward. What they often ignore is the forestay is generating a lot of force athwartships, and the further out on a 'crane fitting' at the masthead, the bigger lever arm it has to twist the mast tube. For our purposes here assume there is no crane fitting, but rather the forestay attaches to the front of the mast tube. It still tries to twist the upper portion of this mast.

    Now resisting this forestay load we appear to have 2 backstays at the masthead that lead down to the transom(s). Very likely only the windward side backstay will be carrying most of the load, Again we assume that these backstays are attached to the aft face of the mast extrusion, or maybe some small crane arrangement. The point is its the windward backstay that is more heavily loaded, and it is also imparting a twist to the mast in these upper regions. So both the forestay and the backstay are twisting the upper portion of this mast in the same direction.

    I don't see any rigging in these upper ranges resisting these twisting loads. That was my concern.
     
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