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Boom Internal Outhaul - Flatten Mainsail & install to shorten boom.

The section protruding beyond the boom supported a block and tackle to tension the mainsail foot.  The problem with the protruding section on Panache is that I sometimes didn't see it coming across.  Yikes!  I guess this is why its called a boom?  The prospect of it whacking my head was not something I looked forward to on my outings.  Since I've had far too many close calls and lost too much coffee, I shortened the boom 9" so now it extends only 6" past the clew.  While shortening solved one problem, it necessitated an internal outhaul due to the reefing lines installed on the outside of the boom. 

At left is the exit block of the outhaul line at the bottom of the (mid) boom.  At right is the shortened boom showing the entry block of the outhaul line. 

Construction - My initial design was a simple 2:1 mechanical advantage block leads aft to the cockpit.  But not having room on the deck to terminate the line I chose a 4:1 block and tackle tied off at the end of the boom as shown below.  While ball bearing blocks have the least internal resistance and are therefore the prime choice, my internal blocks are equipped with smooth turning bronze bushings.  The exit blocks are equipped with ball bearings.  Since I didn't want to perform extensive machining to install the exit block at the top of the boom, I installed it on the side and looped the line through the clew back to the end of the boom.  This balanced the pull on the clew but added some internal resistance.  All line is 5/16" prestretched polyester.  All blocks and the end casting are mounted with aluminum pop rivets with marine adhesive between metal surfaces.  Look at the diagram below to see how the control lines are installed.  Three lines are required.  One of the static lines is attached inside the boom at the gooseneck.  (Remove the casting to secure this line).  The other static line exits at the free end of the boom, through the side mounted exit block, to the mainsail clew.  The remaining control line exists at the middle of the boom to an exit block then through a captive jam cleat to hold the tension while sailing.  To prevent an internal jamb, adjust the lengths of the three lines to position the internal blocks such that they never jamb against the bottom exit block or whatever else you have inside your boom.  The correct relative position is shown in the diagram below.  In the above left photo I've pulled the sail cover back to reveal the bottom exit block and jam cleat.  Note that the style of jam cleat I used holds the line captivate, make cleating easier in a rough seaway.  The line exists the boom about half way so it is within reach when the boom is 45⁰ out.

Conclusion - With the shorter boom I can now stand astride the tiller, steering with my knees and focus on where I'm going without fear of a concussion from the boom.  I can also finish my coffee to the last drop!  With the outhaul adjustment in the middle of the boom, I can adjust the tension regardless of the position of the boom, thereby maintaining sail balance and drive.  There is sufficient mechanical advantage to tension the foot of the mainsail well beyond what is required.  You don't have to be a deck ape to perform this job!  The only problem I've experienced, is dealing with the internal resistance to release the tension for light air sailing.  This merely requires that I pull some slack into the line and push the foot of the mainsail forward.  (Seems like a dumb thing to say but it works).
"One day my buddy and I were sailing in fairly light winds and he thought the mainsail was too flat, while I thought the sail was loose enough, having no tension on the foot.  By moving the clew forward 6 inches and inducing wrinkles in the foot, we gained another knot of speed.  It was obviously a good experiment.  You learn something new every day!"

NOTE - Unfortunately I can only guess at what the factory version of the outhaul line looks like.  Panache did have a block and tackle between the clew and the end of the boom but it was not factory hardware.  The previous owners of Panache changed this long before I bought her.  This is a similar system to what Panache had.
 

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