I have found that an 8:1 purchase is essential for on-the-fly trimming of the large race sails used in Formula Racing. The system shown here works fairly well, and I can usually make pretty fine adjustments while going upwind, unless i'm really overpowered. There are many different ways to rig an adjustable outhaul, and i've tried a few of them. If you have any comments, or if you think you have a better way, let me know; jfeehan@ix.netcom.com
To achieve an 8:1 purchase overall, I have a 4:1 system at the tailpiece (purple line),
which is inside a 2:1 cascade (red line) on each of the boom arms. The blocks are
all 16mm Harken Airblocks, which provide a noticeable reduction in friction when compared
with the integrated sheaves that come in either the HPL or Fiberspar booms. The cleat
shown is the Clamcleat CL244. A newer version of this cleat has a hole which can serve
as a becket, so you don't have to tie the end of the red line to the boom.
The best thing about this setup is that it is extremely quick to rig. the only
step in rigging/unrigging is to tie/untie (i use a square knot) the green line to
the clew of the sail. the whole assembly is left threaded at all times. Attaching
this outhaul is actually quicker than tieing off a non-adjustable outhaul.
When switching sail sizes it may be necessary to lengthen or shorten the line in the
4:1 part to keep the right range of adjustment. I use one piece of line, and just change
the position of the knot holding one of the single blocks.
I use 1/8" uncovered spectra for the 4:1 part, and a 3/16" low-stretch covered line for the
2:1 part so that it is easy on the hands.
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At the tailpiece i use 3 harken 16mm airblocks. Two of them are Harken #432 pivot cheek blocks, which are attached by bolts through the existing holes in the tailpiece. No holes need to be drilled in either the HPL or Fiberspar booms. Between the cheek blocks, i use a Harken #404 single block. This block is anchored, with a short piece of prestretch, around one of the internal sheaves, as can be seen in the photo below. |
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This photo shows how the center single block is tied on to a sheave in the boom. The main reason I did this was to avoid drilling any holes, but it turns out that it allows the block to rise up and point at the clew of the sail keeping the lead fair no matter how high the clew rises. |
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From the tailpiece, the 1/8" spectra leads to a Harken #406 double block. As I mentioned above, the double block never needs to be removed - it is left on the boom. To rig the sail, the only step is to tie the blue line to the clew of the sail. I use a piece of line about 8" long, and pass it through the grommet of the sail and the shackle on the double block, several times and then tie it off with a square knot. It takes only a few seconds. |
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When the outhaul is eased downwind, the clew tends to rise up. In the arrangement I use, the center block can swing up to follow the clew, maintaining a good lead for the line on this block. In general, there is little load on the line when the outhaul is eased, so having a fair lead when eased isn't that important, but it may help to reduce chafe on the line. |
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The 1/8" spectra coming from the tail is tied to a Harken #404 single block. The 3/16" line is fixed to the boom with a clove hitch. It leads through the single block and back through the cleat, a Clamcleat #CL244, providing a 2:1 cascade outside the 4:1 purchase at the tail. The new version of the clamcleat #244, which I have on another boom, has a hole to serve as a becket where the line can be dead-ended with an overhand knot. I like to use a thicker line for this part of the system so that it is easy to trim. Not shown here is a piece of 1/8" shock cord which attaches to the tail of the 3/16" line, goes around the mast, and attaches to the tail of the 3/16" line on the other arm. The shock cord keeps the tail of the line from getting twisted around the boom arm while sailing. |
Hardware
3 Harken 404 single blocks
2 Harken 432 pivot cheek blocks
2 stainless fasteners to attach cheek blocks
1 Harken 406 double block
2 Clamcleat 244 boom cleats
Line
2 72" lengths of 3/16" covered line
1 110" length of 1/8" uncovered spectra
2 8" lengths of prestretch or spectra
1 60" length of 1/8" shock cord
Line lengths will depend on your boom and sail sizes. The lengths suggested here are
what I use on a Fiberspar 220-268 cm boom with a 9.4m2 sail. I haven't really got
the exact lengths worked out, and my lines are a little long.
Clamcleat
Harken
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