Tuning
The 707 is undoubtedly the ‘Sport Boat’ success story thus far, with its main strength being ease of operation and tight class rules. The class limitations on sail inventory make the boat simple to sail, fun, and affordable. With each of the three sails having to cover the whole spectrum of sailing conditions, it is important to be able to get the most out of them at all times. As with all tuning guides, this is just that, a guide. This information should not be taken as absolute. It is impossible to sail strictly by the numbers. Trim and tune are dynamic, requiring constant changes to get the most from the boat. It is more important to understand the concepts behind tuning and the effects of the different controls so that you can learn how to shift gears. Keep an open mind and experiment in changing conditions to determine the right combination for the moment, or simply what works for your sailing style. There is no one way to make your boat go fast. The single most important thing is to recognise when you are slow and to do something about it.
Rig Tune and Basic Set Up
There are three goals to achieve in basic set up:
- Set forestay to maximum length
- Centre the mast in the middle of the boat and ensure that the mast is in column athwartships
- Set the correct amount of pre-bend and forestay tension for the conditions.
Forestay tension and mastbend are the key variables in adapting the rig setup to specific conditions. As with all fractional rigs with swept back spreaders, forestay tension is directly related to shroud tension. Strong winds require a tighter overall setup with more pre-bend. Medium winds call for a fairly tight rig with a straighter mast. Very light airs call for a softer rig but with more pre-bend again. In all conditions the forestay length should be set to maximum. Remember that in addition to keeping the mast in column side to side, the cap shrouds also help to control forestay tension, and the lowers act like checkstays and control mastbend. With this in mind the following should provide a sound starting point:
Mast rake: Class rules prohibit the addition of toggles or any other means of altering the length of the forestay as supplied with the boat. However, the forestay should be set as long as is possible, thus providing maximum rake. With the rig tension set to base settings (see below) the distance from the top of the mast to the after edge of the transom should be 10.80m (this measurement was taken by hoisting a tape measure on the main halyard with the shackle pulled up hard to the sheave)
Centre the mast: With the rigging fairly loose hoist a tape measure on the main halyard and measure down to a point at the chainplates on each side of the boat. If the measurement is the same both sides (or within a few millimetres) the mast is upright. Once the mast is upright, you can begin to tighten the cap shrouds, making sure that you wind an even number of turns on each side. Wind on about 8 turns past hand tight. Now you can begin to wind on the lowers, again winding on an even number of turns each side, but making sure that the mast is straight side to side. Winding turns on the lowers will straighten the mast. Put enough turns on until you are left with about 70 mm of pre-bend (you can check this by sighting up the aft edge of the mast).
Shroud tension: Your mast should now be upright in the boat with approximately the right amount of pre-bend in it. The shroud tensions now need to be fine tuned. Using a Loos gauge (rig tension meter) the cap shrouds should be tensioned to read 21 measured at eye height, the lowers should be 19 at eye height. Using these measurements, the pre-bend should remain at about 40mm. The critical measurement is the pre-bend, do not worry if the tensions are +/- a little. These measurements should be regarded as your ‘base’ settings.
Rig tension for conditions: Remember that what we are trying to achieve is pre-bend in light air but with forestay sag, pre-bend in heavy air with as little forestay sag as possible, and a straighter more powerful rig for the medium airs. Use the following table as a guide
True Wind Speed : Lower Shrouds : Upper Shrouds
0-8 knots : Ease 3 turns : Ease 1 ½ turns
8-12 knots : Base setting : Base setting
12-18 knots : Base setting : Tighten 2 turns
18 knots + : Base setting : Tighten 5 turns from base
These changes are made for two reasons; firstly to control mastbend, and secondly to control forestay tension.