Understanding Sails and Sailing

Efficient Sailing 
Some cruising sails are still made like this. The maximum camber of a sail should be somewhat forward of the middle of its cross-section. In practice this varies to a degree with what sort of sail it is and how hard the wind is blowing. As the breeze hardens, the power of the fullcut sail will become too great for the boat. It must then be flattened or reefed, if either is possible; or changed for a different sail if not.

This requirement is underlined by the fact that as the wind increases, a sail naturally becomes fuller and the point of maximum camber is blown aft towards the leech. Most sails twist away from the wind in their upper sections. When a boat sails along, the wind she actually experiences is a composite known as apparent wind. This phantom combines with the true wind to generate the actual breeze across the sails. Clearly, the faster the true wind for a given boat speed, the less will be the interference caused by the boat's movement. If the upper part of the sail can be twisted to take advantage of this, its resultant force will produce a larger forward component than that being delivered by the lower section of the same area of canvas.

In the case of a fractional rig, the upper section of the mainsail cuts undisturbed air, while the lower parts receive their wind already bent further aft by the headsails. Twist control is vital if the top of the sail is not to be stalled completely.

Shaping the headsails 
In most boats, the primary tool for headsail camber control is the halyard winch. Hoist the sail, then steer the boat on, or nearly on a closehauled heading. Now look up at the mid-part of the sail. If it is too far aft, tension up the halyard and watch the draught move forward. If the sail seems susceptible to this treatment, check it again once your boat speed has built up. The apparent wind will now be greater and the sail may require some adjustment. It's important to do this with your fully open roller reefing genoa as well as a hanked-on sail.

The sail should now be overpowering the boat if the sailmaker and the designer got their sums right. The converse of keeping your sails reasonably flat as the wind hardens is that a sail can sometimes be set up to be too shallow-cambered. It will then lack the power to drive the boat in light airs. If the sail seems lifeless, ease the halyard, and the sheet too if necessary, so as to power up the canvas.
Attention to the luff of the sail may cause the leech to require service. The leechline, if fitted, is a light piece of small stuff sewn into the trailing edge of the sail. If the leech is already hooked, slack away the line as far as the sail will let you.

Most boats have these on sliders. If yours doesn't, the sail must be cut to the position of the fixed leads.
Sheet-lead positions are crucial. When the helmsman brings the sail a little too close to the wind from closehauled or a close reach, the luff should lift evenly all the way up. If the bottom of the luff lifts first, the lead is too far forward, making the leech too tight so that the sail is not twisting enough. The windward ones will always flick up just before the sail lifts. Shaping the mainsails

As in a headsail, mainsail camber is largely controlled by luff tension. However, sails on boats with any pretension to performance generally also offer a clew outhaul. The effects of this will extend approximately to the lower third of the sail. The more powerful sail of a fractional rigger should carry its maximum camber somewhat further forward, but still with a flat, gentle entry.

Mainsail twist is highly controllable on a modern yacht. On a race boat, the powerful kicker may be brought into service even closehauled to help flatten the sail. I've heard people complain along the lines of `All this sail shape nonsense is for the boy racers. Sail combinations

Una-rigged craft often sail excellently. From time immemorial, therefore, sail plans have been divided.
Because individual sails are set forward and abaft the centre of lateral resistance (CLR) about which the boat effectively pivots, they can be sheeted so as to balance her steering characteristics. Secondly, the slot between two sails produces a venturi effect, accelerating the air which is squeezed through it. The result is weather helm. Lee helm is a dismal condition.

Hull balance
In addition to the disposition of her sail plan, a yacht's helm balance varies depending on how much she is heeling. As she heels to leeward, any tendency to weather helm will increase. Rolling to windward generates lee helm. As the boat heels, the centre of effort of the mast and sails moves outboard.

Shortening sail  
Shortening sail as the wind strengthens is part of the sailor's everyday life. Similarly, a reef in the mainsail moves the leech inboard along the boom. The sails are therefore generating less weather helm than if the yacht were spreading everything she carried. It would be unwise to generalise about where to begin sail reductions. Poorer gears produce a dismally reefed sail which looks more like a flour bag than a number 3 genoa. None the less, all such arrangements give the benefit of instant sail area adjustment. It can therefore be used routinely for heavy weather sailing.

Mainsail reefing systems now exist which are way in advance of the old 'round-the-boom' roller reefing. Mainsail reefing options therefore subdivide into three choices: in-mast roller, inboom or round-boom roller, and traditional gear for reducing the sail in `slabs' at the foot.

Cruising chutes
Today's Bermudan-rigged yachts have much in their favour, but sailing downwind in light and moderate going is not one of them. Sailmakers will deliver them complete with a `snuffer' - a sort of sleeve which rolls down over the sail, spilling its wind miraculously.