On 2/14/13 a "mock-up" was assembled again. The pulley area will be padded:

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Looking aft; the lines at the boom will be spaced two ft. apart:

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Looking fwd.; the lines at the boom will be spaced two ft. apart:

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The black line and bungee keeps tension on the forward "tow" lines:

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Connections at the tow eye:

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Connections (and boom material) revised February 24, 2013:

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ANOTHER PHOTO
ANOTHER PHOTO

(on facebook 2/27) I've revised the (ski) boom and its connectors. Now using tube of unknown aluminum alloy, with "schedule 40" wall. Turned some machinable aluminum to receive shackle. An SS 10-24 flat-head bolt will secure the two pieces. Same detail inboard and outboard. Another slip-fit tube ("schedule 40" wall) outside strengthens the tube.
Top = new
Middle = original
Bottom = aluminum "plug" to receive shackle
New outside tube and SS bolt not shown here.

Frank Miklos sez "I like a little better ..."

Frank, -- :-)
I'm finding this to a very interesting study in forces. Now thinking of loads mostly two:
1) the skier being pulled from bow lift eye, and
2) the skier being held away from the boat via the boom.
The buoyancy of the skier means there is not much vertical bending load.

The "truss." The "lift line" will be adjustable in length and will terminate at the boom farther out the boom:

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That's a jib sheet cleat from a Flying Scot:

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Two views of the truss. Carpet protects boat deck from marring. The small white line keeps the truss from moving fore or aft:

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Click to enlarge.