It's a fine Saturday morning at the launching ramp... and the number of trailer yachts gliding into the water is visible proof that more and more New Zealanders are enjoying the access to the sea and camaraderie provided by trailer yachts. But as the number of trailer yachts continues to increase, so does the proportion of people unfamiliar with the finer points of sailing and setting up their rigs. This tuning guide is intended for those who just want to get the best out of their boat and their sailing pleasure, and for those keen to compete, both the newcomer and the old salt.

For want of a better place let's start at the top of the mast. The first item needed is a wind pennant and I recommend the arrow or Windex type. The advantage over a flag-on- a-stick type is in its stability and accuracy of direction; it doesn't oscillate wildly but changes direction in a steady manner unless there is practically no air, when it will sometimes rotate slowly through 360 degrees. It is important that it is evenly balanced (not heavy at one end) for maximum efficiency, while for easy visibility it should be mounted as near as possible to the aft face of the mast or, on larger boats, set out aft of the top of the mast on a short strut (Figure 1).

It is also important that it stands well clear of the top of the mast so that it is not affected by updraft, or tip vortex, from the top of the main. I suggest a range from 220mm to 260mm as most suitable. For this reason, smaller dinghy windicators are not really suitable.

The rake and length of the spreaders also influence mast bend and therefore shape. Basically, longer spreaders, or more rake in them, will increase mast bend. Where the boat is tender this is often an advantage, whereas a stiffer boat is better with less bend. Bear in mind that excessive mast bend induces forestay sag and this will have its own detrimental effect on boat speed and stability unless the jib is cut to suit. The longer the forestay the more acute the problem. Forestay sag deepens the draft in the upper portion of the jib and moves it aft, hooking the leech, back-winding the main and choking the slot (Figure 3).

A method of inducing or reducing mastbend is to use the heel of the mast (Figure 4). If the base is cut at a slight angle, applying pressure to the for'ard or aft edge of it will induce mast bend in the respective direction. The effect is quite small but may be all that is required to make the difference. Pressure on the aft edge (1) would be used with a mast larger than required and pressure on the for'ard edge (2) with a mast too light. This effect is similar to, although not as dramatic as, chocking a mast at deck level when keel-stepped. This method should be used with caution as the edge of the mast can be easily crushed.

Because the upper section of mast is unstayed, the leech of the main is controlled by mainsheet tension. For this reason it is best to have a stiff boom which bends only a little. I prefer a mainsheet system in from the end of the boom - referred to as central sheeting although in fact it should not be in the centre of the boom as this requires too much sheet tension to control the leech of the main. It also requires a rather large boom if it is to remain stiff.

If the mainsheet is to be taken to the end of the mainboom, it should be no further aft than the clew position of the mainsail as it can create an upward bend in the centre of the boom under load, which serves to increase draft in the sail at the very time you wish to reduce it. One of the principal reasons for keeping the mainsheet further forward, however, is to get greater range from a shorter traveller (Figure 5).

Because of the unsupported top- mast section, mainsheet tension is critical. It is important to put a mark on the mainsheet at what you consider to be about the right tension for moderate airs, then work around that mark. A little more tension will be needed in fresh airs, a lot less (sometimes up to 600mm less) in very light airs.

As the mainsail of a trailer yacht is usually of fairly low aspect ratio it is easy to overtrim the mainsheet, tightening the leech and reducing boatspeed. A good way of assessing this is to sight up the sail from underneath the mainboom to the top batten and make sure this is not above a line parallel with the boom (Figure 7) - this, of course, being not too easy to do in fresh airs! In the very light and fresh, the top batten should be falling off this line between 10 and 20 degrees.

Leech tell-tales are generally placed on the main at each end of the batten pockets. These consist of strips of light nylon spinnaker cloth approximately 25mm wide x 230mm long (Figure 8). They are a good indicator of mainsheet tension as if one or more are not flowing (except in very light airs), too much tension is indicated.

Here also boom vang tension is applicable in light airs as it is not much use having the mainsheet well eased if the vang is too tight. In the very light, 25mm on the boom vang can be critical.

The most important (and difficult) tell-tale to set is at the second batten down. This and the top one are the first affected by too much leech tension, whether from mainsheet or boom vang. However, the second is also usually the intersection of the jib with the mast and the amount of twist in the upper part of the jib can also affect it. If the others are flowing and this is not, try easing the jib sheet or shifting the lead aft to twist the upper part of the jib a little more.

A wool tell-tale is attached halfway across the main just above or below the top batten and by a combination of this and the respective leech ribbon it is easy to tell if the airflow is stalled either on the wind or reaching under main and jib. Adjustment is dictated by mainsheet and vang tension, luff tension and traveller position (Figure 9)

To achieve the flatter shape higher up the main without a permanent backstay it is necessary to ease main halyard tension until small wrinkles start to form from the luff. This, combined with pulling the traveller up the mainsheet track and easing the sheet, will flatten the section (chord depth) of the sail (Figure 13).

As with all rules there are, of course, exceptions, and in this case one is when there is more sea than wind, as in a dying breeze. This is when a little more draft is warranted, but accompanied by an easing of the mainsheet to induce more twist and by pulling the boat off to "foot" through the water for boatspeed.

Foot tension should always be eased to make the sail as full as possible when reaching, unless in a fresh breeze.

Looking next at the cunningham. First, always hoist the main to the maximum height possible on the mast (unless this over-tensions the luff) as the lower down the headboard is the stiffer the mast will become - and what is the use of more mast above the sail than necessary? The luff of the main should be stretched just tight enough to remove lateral wrinkles (otherwise as explained in very light airs). As the breeze freshens it will be necessary to apply cunningham tension (or gooseneck down) to maintain this state. As the breeze freshens further, more tension still needs to be applied to help induce mast bend yet keep the draft in the for'ard part of the sail.

Pulling the luff tight enough to induce a crease up the luff of the main before going out on a fresh day puts slack material up against the mast, leaving the mast free to move for'ard in the centre without restriction. The mast will bend only as far as the sail will allow before severely distorting the sail if the pressure is great enough and the mast soft enough.

When the boat starts to become overpowered, ease the mainsheet traveller down the track. This should be done before easing the mainsheet. At this point the mainsheet should be quite hard, bending the mast and flattening the main. If you ease mainsheet it will simply create more drive in the sail and mean easing the sheet still further till the main flogs.

Once having reached the limit of the mainsheet traveller and providing the boom is strong enough, put the vang on hard and ease the mainsheet further. This will have the effect of a longer traveller. By keeping the mast bent and sail flat, the boat will stand up longer before you have to start reefing. Tight mainsheet or vang also helps keep the forestay tighter, thus reducing heeling force.

In addition to luff tell-tales I like to put another ribbon (like on the main) about a quarter way down the leech from the head. By keeping this flowing in light airs, a clear airflow is maintained over the lee side of the main which, as mentioned earlier, keeps the upper mainsail leech telltales working. Basically this tell-tale indicates (in light airs) the amount of twist required in the head of the jib (Figure 15).

In some trailer yachts where the jib barely overlaps the mast (such as the Farr 6000), pulling on the weather sheet allows the clew of the jib to be barber-hauled to weather, decreasing the sheeting angle and putting more drive in the lower part of the jib while at the same time twisting the head off. In very light airs I prefer no barber-hauling, but in light to moderate breezes a reasonable degree of barber-hauling is a definite advantage. This needs to be coupled with some easing of the leeward jib.

As the wind freshens, the barber- hauler is released and sheet tension increased, reducing chord depth in the sail and controlling excessive twist in the upper leech of the jib.

Jib halyard tension is also critical and if you haven\'t a winch, a trucker\'s hitch (Figure 16) will do the job. Always tension the halyard enough to prevent scalloping between the jib hanks, thus giving a fair flow off the luff of the jib. If you overtension, a crease will appear up the sail on the luff edge.

Because of the nature of the rig - i.e. forestay kept reasonably straight by mainsheet tension - it is usually necessary to induce this crease when running downwind so that when coming hard on the wind with the forestay taking some sag, there is enough luff tension to prevent scalloping between the hanks. Better to overtension than undertension as it is easier to ease off than increase tension.

With an overlapping genoa, some backwinding of the main will be inevitable in moderate and fresh breezes. So long as the main is kept flat low down this must be accepted, though the rules of mainsheet trim still apply. The mainsheet traveller will still be dropped down the track to keep the boat upright even though this will increase the backwind rather than reef.

With a fractional rig, once the main is reefed the de-powering effect of the bending of the unsupported topmast is lost, the mast becomes stiffer and the mainsail fuller. However, once the boat becomes overpowered, even with the use of all trim adjustments mentioned previously, reefing becomes necessary to keep the boat on a reasonable angle of heel. If the genoa is full hoist on the forestay, a cunningham eye is necessary in the jib to further tension the luff.