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 (V’s) outside stays are discontinuous and adjusted at the chainplate, and second spreader for the topmast (V3).
The diagonals (D’s) are adjustable at the deck, while the D2’s are adjustable at second spreader ends.

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.

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 V1’s (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 & D2’s 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.

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 V3’s should be slack. After the required tension has been achieved, tighten up the masthead V3’s 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 downwind, the V’s 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.