Balestron modification?

Discussion in 'Sailboats' started by plebian, Sep 3, 2015.

  1. plebian
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    plebian Junior Member

    Hey guys, recently my wife has being going through some medical complications that prevent her from crewing, so I've been stuck going completely solo when I take my mac 26 classic out. I've been looking for ways to reduce the load on myself while I casually sail and have been reading alot on aerorig/balestron configuration and was wondering why all I see is complete mast replacement for a stayless 360° system instead of just a main boom extension that would hold the jib and only rotate 180° (well more like 170° considering spreaders). Since I couldn't find anything like I desired I started mocking it up on paper and would like some feedback from experienced designers on potential problems that I can't foresee. Keep in mind this is for casual sailing, not racing, and I don't take the boat out in high winds. The actual contruction of the clamp would probably end up more square around the mast and made out of stainless unistrut.
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  2. gonzo
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    gonzo Senior Member

    The masthead and the brackets for the spreaders and lower shrouds will also have to rotate simultaneously to maintain the proper geometry. Further, the mast step has to have a bearing that will support the load of the rig and allow it to rotate.
     
  3. plebian
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    plebian Junior Member

    Well, it's a mac 26, changing the j-bolt that holds the boom from a 3/8" to a 1/2" to hold another 40 lbs is almost nothing. Also, my proportions on the downward view on the clamp is wrong, it would have to be 2x the diameter and the j-bolt length so when turned to 85 degrees it would look like this:
    [​IMG]


    (I know it's 90 in the drawing, but drawing an angle in microsoft paint is a pain).
     
  4. gonzo
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    gonzo Senior Member

    The whole rig needs to turn. Also, the spar needs some kind of structural support to keep it from bending up. The tension on the ends will be pretty high. Simply attaching the end of a tube to a ring will not work.
     
  5. plebian
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    plebian Junior Member

    You think it will be enough for a 9' X 1 1/2' of stainless unistrut to buckle if supported a foot in on the bracket?
     
  6. plebian
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    plebian Junior Member

    I guess I can weld a 1' 45 degree bracket on the end and rig a cable to give downforce from there, like this:
    [​IMG]
     
  7. plebian
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    plebian Junior Member

    What's your reasoning for having to rotate the whole rig if I don't intend on turning it more than 85 degrees in either direction off center? Unlike the aerorigs, I have no intent to ever flip the jib past the shrouds.
     
  8. gonzo
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    gonzo Senior Member

    Assuming the rigging won't have to turn, the main structural problem is the ring around the mast. You need to treat is as a mast. The angle between the cable and the end should be 14 degrees or more. However, this introduces a huge amount of tension, which your existing boom may not be able to handle. Also, the boom for the main and the jib need to be a single rigid structure, both with a truss system on the lower part.
     
  9. PAR
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    PAR Yacht Designer/Builder

    I see a number of engineering issues, but the main thing I'd worry about is point loading on the mast, when the rig is pressed. The current mast is a compression post and doesn't tolerate much wall pressure, before it buckles.
     
  10. plebian
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    plebian Junior Member

    How much more during a press than it already does when I use a jib pole are we talking about? I had assumed not that much since the force is already taken through the forestay to the masthead where the sail rides now. The most pressed point I foresee is whatever part of the clamp ring is leeward, as the booms would want force back on it and push the rig into a "V", I just didn't know if it would ever see winds hard enough to cause that with 2 sails with as little surface as the mac has.

    What I mean is, it's not a large sailplan as it is. It's weight that Prindle 19 booms have been handling for decades, and I'm sure you've seen one of those by now, aluminum tube smaller than the stainless unistrut that I was planning on using.
     
  11. plebian
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    plebian Junior Member

    and I was wrong about the 3/8 j-bolt that holds the main boom now, I just looked at it and it's a 5/16.
     

  12. sharpii2
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    sharpii2 Senior Member

    The number one job will be maintaining adequate luff tension for the jib. This means:

    1.) the boom combination cannot be allowed to bend significantly. The structure you have drawn probably won't work, because the boom was never designed to be a cantilever structure. It will probably bend over at the end of its attachment point. Same for the forward boom. In order to make this strong enough, the boom will have to be much thicker, made of much stronger material, or both. A spreader could be added to the ring with a cable running to the ends of both booms. To be effective, this spreader would have to be about one forth the length of the aft boom, minus half the ring diameter.

    2.) once the sideways bend is taken care of, something has to be done about the vertical bend. Another set of cables would have to attach to the mast ring about one forth the longest boom length below the booms. The other ends would attach to the end of the booms. Your ring has now become a barrel.

    As you can see, this would be a lot more trouble than it originally appeared to be.

    Why not keep the original configuration and just make it easier to use?

    Assuming money is an object (it almost always is) let's look at the least expensive alterations.

    The first would be a down haul for the jib, so you can take it down without having to go out on the fore deck. This will require a well placed small pulley and some relatively thin line. The pulley attaches at the base of the fore stay and the line passes through the jib hanks, to attach to the top of the jib. The other end leads to the mast or the cockpit.

    Next, you can consider putting a boom on the jib. It won't be as efficient as the present two sheet set up, but it would be self tacking.

    Both of these mods combined would be far cheaper than what you propose.
     
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