Subject: Re: beams and trailers
From: Mike Crawford
Date: 2/5/2006, 12:27 PM
To: rob dalton


  I'm becoming more of a fan of an expanding trailer that stores the lw hull on its side, extends out, inserts masts horizontally, and then winches to vertical using the beams.  It probably can't much simpler than that, and you won't find a way to make the beams lighter, stronger, cheaper, or more reliable.  Simple, light, strong, cheap, and reliable are all good things.

  I then see the challenge being threefold:

  a) Supporting both hulls as the trailer is widened.  They can be temporarily supported by posts once the trailer is at full width, but you'd need to have a pretty stable and sturdy trailer to get there.

  b) Keeping the ww hull vertical.  The trailer will have to have some pretty tall and sturdy bunks for the ww hull to keep the weight of the sleeping pod from rotating it downward.

  c)  Rotating the lw hull.  This shouldn't be too much of a problem as long as the bunks are tall enough to support it well on its side.  The whole bunk could pivot on a single axle on the outboard side.


  I've also realized that my dream of the scissors-beam scheme has a major flaw -- the steering system.  Steering would have to be mounted on the main hull for that to work, and not on the walkway.  I'll have to spend some time thinking about that one.  This would also be a problem for the farrier system, making it difficult to use either scheme to reduce beam for entry into a slip.

  The scissors beams could also be a problem for the ww hull beam.  Right now the collapsed width of the boat would be 12-8", eight inches wider than the legal maximum for non-escort trailering.  I can't be entirely sure of this because I haven't seen any official dimensions, but I've dimensioned the online drawings using some design software (assuming the lw hull is 50' long), and this is what I've come up with.  I was going to print the renderings out and use a draughting scale, but then I realized that it would probably take less time to do it electronically, and then I'd have a nice file I can print out.  A pdf file is attached, in case you're curious.

  This means that either one of the hulls would have to shrink somewhat, or the lw hull would need to be stored on its side.

  You could make the argument that it would be easier to assemble the boat with the lw hull on its side, and that this would also yield a narrower trailering width of less than 11', which would be nice.  You could even add a foot or two of width to the ww hull without affecting this equation, providing a larger cockpit and more storage area inside.  Of course, this would add more weight, but at least it would be an option.

  Rob really has thought things through.


       - Mike



rob dalton wrote:
Roughly how I imagined it. You could use your boom as the gin poles and then use the two booms to make  a a bipod to provide support for a lightweight block and tackle. Possibly the bipod and a block and tackle could do the original lift but I don't know if it would be quite long enough to lift the mast high enough to pivot it in position.With a 9m bipod it would be a piece of. The main difficulty is setting up the boat with various sockets and rope attachment points. Check out robs original Harry in the articles section for how he worked on a big schooner rigged wingmast.

Mike Crawford <jmichael@gwi.net> wrote:
<<I suppose the mast could be raised on a pivot at the base, when vertical remove the pivot and somehow make sure the whole thing doesn't fall down.  >>

  That's it.  Or at least that's the way Franke does it on cat2fold.

  The mast is supported by a roller at the top, and then pinned to a sleeve that gets inserted into the hole on deck.  This sleeve extends about 10cm higher on one side than the other, "missing" half the sleeve on the aft side where the mast is inserted.  Lines triangulate out to each side to provide lateral support, while a halyard goes over a gin pole and down to a winch, and another line runs from the mast to the boat in order to prevent the mast from tipping over once it reaches vertical.

  He then winches the mast to vertical.  Once it's there, he fastens the missing half of the sleeve to make it complete, grabbing the mast at its base.  He then uses a neat little lift that's about one meter high and 30 cm wide with a crank at the top.  The crank is a 1cm rod/axle that extends out to a handle that's maybe 30 cm long.  A line wraps around this axle many times and then fastens to the mast.  He "winches" the whole mast up few centimeters with the lift, removes the pin at the base, and then lowers it with the crank.  With the 30:1 power of that handle, even an 80 kg mast wouldn't be an issue.

  There would still be some problems adapting this to a proa, but I think it's possible.

       - Mike



rob dalton wrote:
The akas can be made perpendicular. But even if they weren't it only needs the pivots to be parallel. The pivots do not need to be perpendicular to the beams. The ends of the beams can sit on a flat suface and be held down but better if they are in a notch. the ends of the beams can be tapered to perpendicular to the hulls as they would have to be for any system of sockets.  James Shannahan's original version of the folding sysstem was very elegant but the extra complexity is a big expense apart from the weight. Also the bridge deck comes either level or below the bottom of the beams. To get the boat to trailering width the lw hull needs to tuck under the bridge deck, preferably on its side. This could be done fairly easily with the expandable trailer. My experience with putting very tall objects into close tolerance holes has not been easy. It needs a gantry to lift the masts from near to their pivot point from almost directly over the hole. I suppose the mast could be raised on a pivot at the base, when vertical remove the pivot and somehow make sure the whole thing doesn't fall down.  
Mike Crawford <jmichael@gwi.net> wrote:

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