Aftmast rigs???

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

  1. brian eiland
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    brian eiland Senior Member

    ...and I wouldn't be able to issue this challenge....:D

     
    Last edited: Oct 13, 2015
  2. markstrimaran
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    markstrimaran Senior Member

    I loose sleep over this

    CT249
    Bermudan rigs can also be extremely cheap, if you get one that allows you to use the sails from a popular racing class. If you ask at the right time (like when the owner's wife is within earshot and wants the garage cleaned out of beautifully-kept sails that have been used 30 times) you can get them for free!*

    Yes I fear my wife might do this to my canoe and kayak mini trimaran project.
     
  3. markstrimaran
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    markstrimaran Senior Member

    Raising an aft mast on a trailer trimaran.

    https://youtu.be/GnmLeCffUBc

    Clip is 4 minutes. It takes me 25 minutes to be sailing after I park.
    The out riggers winch and mast winch are drill or manually power worm gear type.
    The roller furler boom takes about 2 minutes to set.
    The aft mast allows a 25' mast that is always stepped on its hinged base. On a 15' boat hull.
    A Bermuda rig would require unstepping the mast for transport. Or a 18' mast perhaps hinged to lay back. Traffic laws allow about 6 feet sticking out behind.
    I usually go sailing after working a 3rd shift. So I keep things very simple. Very frequently I get back to the boat ramp at 2 am. So derigging in the dark, has its own problems. With out an aft mast. I do not think day sailing would be very enjoyable.
     
  4. CT249
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    CT249 Senior Member

    Nice work Mark - that setup suits your desires nicely.
     
  5. sharpii2
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    sharpii2 Senior Member

    For most ocean crossing purposes, the square rig was superior to the latteen.

    The reasons for this are:

    1.) Ocean voyages were predominately downwind, which negated the lateen rigs bigest advantage; it was a far superior upwind rig, and
    2.) The lateen rig required a yard that was at least twice the length of that required by a square rig, for the same sail area. This yard also had to be shifted from one side of the mast to the other, everytime tacks were changed.

    I doubt this study, which is constantly being quoted, proves that the mast aft rig is generally superior.

    Their data may point in that direction, but one has to be careful about how they came up with these numbers.

    Aparently they tested a scale model with a wind tunnel.

    And apparently they tested mainly on one point of sailing, upwind.

    The problem with any boomless sail is that its clew line needs to be attaced to a different point on the hull for every point of sailing, to get the best out of it.

    Also, to get the best out of any sail, it has to be sheeted to its best angle to the wind. This is especially true for a sail which has a clean leading edge

    with a wind tunnel, these requirements are easy to acommodate. The rig is held to a fixed angle to the "wind" which never changes its direction--even slightly.

    As for the scale model itself, being on a much smaller scale than a real cruising boat, there are some loads that just don't scale down easily. One of those is the leading edge tension. To get a jib to set well requires a rather straight leading edge. To get this straight leading edge requires quite a bit of tension. The biger the jib is, the more true this is.

    My guess is that with the model such tensions were easier to achieve.

    On a full scale cruising boat, weighing in at several tons, this will almost certainly prove harder to do. It will require a stronger, stiffer mast section and mor intricate staying.

    Without this, much of its upwind advantage is lost.

    I find it very concievable that a bendy spar fractional sloop may well be the superior upwind animal in real life conditions. The main reasons I say this is are:

    1.) the bendy mast, which sets mostly the main sail, can be lighter for its length than the stiffly stayed mast aft counter part.

    2.) it can have simpler standing rigging, with far fewer stays and shrouds and have ones that have smaller section too, and

    3.) In any kind of a seaway, the wind does not blow from a steady direction. And the pitching and rolling of the boat constantly changes the angle of attack on the sails, due to changing apparent wind, thus making it impossible to come near the accuracy in getting perfect sheeting angles, which gives the clean leading edge sail most of its superiority.

    For these three reasons, it is clear to me why the mast aft rig never made it to the race course. It was simply more economical to set the mast a little further forward and set a tiny main behind it, until the bendy rigs took over.
    Because hey, man, I'm getting a little less head sail, with proportionately less staying tensions, and I'm getting 15 to 20% more sail area for the same length mast in the bargain.
     
  6. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Shifting the lateen yard to the other side of the mast?
    I suspect they did it the way I will. See-saw the yard to tack.
    The yard tip aloft gets hauled down to the deck and the opposite end goes aloft.
    Now the yard is on the other side and the sail on other tack. :D
     
  7. Kojii
    Joined: Oct 2006
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    Kojii All is remodelling

    Heading south

    Heading south - Rounded Pt misConception few weeks ago under staysail in 20 knots with following swell. This flying staysail is the power, oddly, to the rig. I highly recommend it for the double headsail delta rig. Very little moment to it, all drive and damping roll effects.
    Previous comment (someone had a real sail under headsail only) on stalling when the genoa is out rang true. So we frequently reduce the big genoa combined with the staysail and get less drag and more speed that with the long-footed genoa.
     
  8. CT249
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    CT249 Senior Member

    Sorry; I just meant to be making the point that there is a lot of evidence from racing that indicates that the rig is NOT faster.

    Of course, you're right, speed is not everything in a rig.
     
  9. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    Happy Columbus Day!
     
  10. sharpii2
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    sharpii2 Senior Member

    Do you mean like this? (see attachments)

    I proposed this scheme in an earlier thread, proposing a possible archaic version of the rig, before it became a true fore-and-aft rig.

    Most reconstruction drawings I have seen are not like this at all.

    With them, there is a definite top and bottom to the yard. The bottom part makes up as little as one third the length.

    Even with my sketch, it is clear to see that the SA would be severely limited with my scheme. Also, notice how long the yard is compared to the boat's Beam.

    A square sail would have a yard half as long, for the same SA, and one that pivoted on only one plane. It would be an awful lot easier to control in a storm, wouldn't you think?
     

    Attached Files:

  11. CT249
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    CT249 Senior Member

    Is there any reason to "suspect" anything? I thought there were lots of descriptions of the way they shifted the lateen yard, and it wasn't by see-sawing the yard. Apart from anything else, that would demand the sail to be symmetrical, and we know from many, many depictions dating back to ancient times that they were normally assymetric.
     
  12. brian eiland
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    brian eiland Senior Member

    I'm surprised that your mast appears not to wander side to side as you raise it,....and I believe I see that you are not applying any 'stabilizing' lines to the sides?

    I had a 36' mast on my Firefly trimaran design, and we raised the mast from the with the help of a gin pole,...somewhat similar to your operation. But we definitely needed side lines to stabilize the situation.
     
  13. brian eiland
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    brian eiland Senior Member

    Overlap Genoa Size on my Aftmast Rig

    Somewhat surprisingly I never did bother to calculate the overlap % of my genoa on the aftmast rig I proposed. I just did it by dropping a straight line down from the masthead in my drawing, then measuring that "J' dimension, then divided that length into the luff perpendicular (LP),....standard method.

    Guess what I came up with?.....slightly less than 104%.

    Surprised even me, as I had just guesstimated it at 110-115% for years.
     

    Attached Files:

  14. hoytedow
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    hoytedow Fly on the Wall - Miss ddt yet?

    Would a symmetrical sail work?
     

  15. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    > Would a symmetrical sail work?

    For a given value of 'work', sure. Most ways of hanging some cloth in the air produce some forward power on many points of sailing.
    The "leech" and "foot" would need to be identical and swap places when the boat tacked and gybed. There'd be an awful lot of rigging though I think. The drawing above seems to cover it - and some of the obvious disadvantages.
    Gybing would be easy enough, but, although I haven't put too much thought at it, I suspect tacking might be a bit of an adventure.
     
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