Tuning Trailer Yachts Part 3
A popular misconception is that the lighter the air the fuller the sail should be. This is not the case, as in light winds the air is travelling too slow to encompass a deep curve and so breaks off before reaching the leech (Figure 12).
Conversely in fresh winds the air is travelling too fast to encompass a deep curve and so breaks away. How ever, by this stage if the main is set up too full it will be backwinded severely by the jib because of the constricted airflow through the slot.
When the air accelerates in light to moderate conditions you can have maximum draft as the air is travelling fast enough to encompass the curve without prematurely breaking away. Basically this means that quite a lot of outhaul tension is used on the foot of the main going to windward so that a crease (fold) starts to form, at rest, in very 1ight airs. This would be eased a little for light to moderate airs, then pulled out hard as the wind freshens.
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.
t is advisable to have tell-tales on the luff of the jib about 150-200mm away from the luff and at quarter, half and three quarter heights. In moderate conditions these tell-tales (or wools) should all luff together when the boat heads up into the wind. To achieve this, keep adjusting the jib and heading up into the wind until all the tell-tales lift together. If the top one is lifting first;the sheet lead needs to go for'ard; conversely if the bottom one is lifting first (Figure 14).
The most important luff wools on a headsail are the leeward ones as these indicate the worst stalling situation. If the boat is a bit overpowered the windward wools can be lifting with the boat still performing well. However, to have the leeward wools stalling is unacceptable.
Don't let wools be your only guide to sail trim as the most important single factor is the angle of heel of the boat. All boats perform best at particular angles of heel for varying conditions and finding and maintaining this optimum angle is of prime importance. It is no use to have all the wools setting but the boat over at 45 degrees.
In very light and fresh airs the jib sheet lead should be moved further aft. In the very light this allows more twist in the head of the sail, opening the slot between main and jib. At the same time ease the sheet, giving more "life" to the sail.
In fresh airs the sheet is kept hard but the effect of sheeting aft twists the upper leech, opening the slot and reducing heeling moment by spilling air from the top of the sail. This, of course, is in conjunction with the mainsheet traveller being let down the track.
In very fresh airs, ease the sheet as well which, coupled with pulling the boat off a few degrees, produces boat- speed and makes her able to drive through the sea better and stand more upright.
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.
It is essential to the boat's performance to have the correct mast rake, This may be obtained from the designer or manufacturer, or set up in the following way:
Correct mast rake is best achieved under moderate conditions. Set the boat up with slight weather helm so that when the tiller is released the boat will veer into the wind. Weather helm can be increased by raking the mast aft. If the boat has weather helm, this can be rectified by raking the mast forward, but not beyond vertical.
If the boat has too much lee or weather helm, the actions of the rudder will be greatly amplified when heeled and the yacht will be difficult to handle. A rule-of-thumb guide is 10cm for every 3m of mastlength.