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Fractional
rig with sidestay masthead support and no backstay. Typically
the T750, T830, and T920.
This type of rig has no backstay and relies on the V3 wires
from the second spreader for masthead support. This rig has
a 2 spreader configuration with additional spreader at the I-point
for MH and fractional Spinnaker support.
Vertical (Vs) outside stays are discontinuous and adjusted
at the chainplate, and second spreader for the topmast (V3).
The diagonals (Ds) are adjustable at the deck, while the
D2s are adjustable at second spreader ends.
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Preparation
Make sure all rigging screws are fully operating smoothly and
lubricated with suitable weatherproof silicon grease.
Strip all wires off the rig, and measure and compare lengths
of each pair without the rigging screw. Note the measurements
and any differences. Check all the spreader and spreader bases
for any movement. Also the mast base for rotaional movent. Any
undue movement should be alleviated.
Installation and Tuning
Stand the rig with the D1, D2 & V3 loose, and set the rig
up to the required rake.
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Measure the rake by hanging a bucket of water from the main
halyard. Measuring the distance from the halyard to the mast
at the deck level. The mast should be as straight as possible
with little or no prebend for this task. When the mast rake
is as required, usually around 3 degrees, lock off the forestay.
Tighten the V1s (with the D1, D2 & V3 slack) until
approximately 150% of the mast setup prebend is achieved. The
mast setup is measured at the spreaders and the I-point, and
can be done by pulling tight the main halyard to the back face
of the mast at the boom gooseneck.
Note: When tightening up any rigging, check the pairs length
against each other with the known original stay measurements.
Progressively tighten both the D1 & D2s until the
mast prebend setup is achieved.
Check the forestay for the right tension. As a guide, a person
should not be able to move the stay more than 60mm at head height.
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If the forestay is too loose, progressively tighten the V1 and
also the D1 & D2 to get the tension on the forestay required.
Make sure that the prebend as required is maintained and the
mast is in column athwartships.
While the tensioning is proceeding, the masthead V3s should
be slack. After the required tension has been achieved, tighten
up the masthead V3s at the second spreader. Being careful
not to over tighten. These stays should only be tightened enough
to support the masthead Gennaker downwind. But slack enough
to allow the mast tip to bend upwind.
Sailing
Sailing downwind, the Vs need only be Tight enough to
keep the mast from bending forward at the top. The leeward stays
should slack when sailing upwind. Once the mast is setup, measure
all of the turnbuckles and record for future reference. In lighter
air, slacken off the forestay approximately 20mm to give more
slop in the forestay and more power in the jibs.
Mast Gate
Where the slot in the deck is provided to form a mast gate,
it is important to have enough purchase to counter the forward
thrust of the mast due to the vang and mainsheet loads. As the
vang is used in heavy weather, The mast gate control will need
to be used to stop the mast bending forward, thus depowering
the rig.
A good rig setup will provide enough excelleration with little
or no tweaking. With the right setup, the topmast should flick
aft and to leeward to open the leech of the mainsail to spill
air when overpowered therefore reducing the need to constantly
trim the mainsheet, and to a lesser extent the traveller. Also,
as more vang and mainsheet is used, the mast will automatically
bend forward in the middle to depower the mainsail by flattening
it.
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