Sail trim for cruisers

There are many reasons for having well trimmed sails other than winning races, but unfortunately that is not always appreciated by the cruising sailor! Guy Waddilove looks at 10 ways to improve your performance and speed up passage-making.

Sailing fast, or even sailing efficiently, is not the sole preserve of racing boats and there are numerous reasons why the cruising sailor should aim to sail at optimum efficiency. However, unfortunately this is often a neglected skill among some in the cruising fraternity.

Sailing faster obviously shortens passage time, and while part of the adventure when cruising is the pleasure of getting to new destinations, the longer spent at sea the higher the risk there is of experiencing bad weather. In the most extreme cases this could mean maintaining a decent speed to get maximum distance away from the predicted route of a hurricane or cyclone. This will allow the sailor to get to an area of potentially less devastating winds than would have been experienced closer to the centre of the system. On a more local scale it could be the difference between getting safely into a port or anchorage before a front comes through or beating the change of tide on a bar or tricky entrance.

As well as reducing potential exposure to bad weather, setting up and trimming sails properly will prolong the life of the sail. Sails do not like flogging and flapping; it breaks down fibres, yarns, glues and just about everything else that ensures the structural integrity of the sail. Allowing a sail to flog will shorten the life of the sail dramatically and at best require repair and service earlier than should be necessary. A properly trimmed sail should not flap or flog.

Trimming the sail to avoid flapping will also reduce noise and vibration on the boat. Reducing noise is beneficial for the comfort of all on board as excessive noise can contribute to fatigue. Additionally vibration, in extreme cases, can have an adverse affect on many parts of the yacht, damaging or shortening the life of other equipment on board.

So, without getting an America’s Cup trimmer on board to train you up, what simple steps can you take to make sure your sails are properly trimmed? The ultimate aim is to have the telltales on the mainsail streaming in a direction as though they are an extension of the sail and the telltales on the headsail flowing along the surface of the sail on both sides (you do need to occasionally check that the telltales are not crusted in salt as this will definitely stop them flowing). How can we attain these goals?

1. Make sure the sail fits

If the sails have been made specifically for the yacht, then this will not be a problem, but if secondhand sails have been bought or even new sails that were built for another yacht are fitted then this could cause problems. As well as fitting along the luff, a headsail will need to be sized correctly along the foot and leech to ensure that it can be properly sheeted. This is less of a problem with mainsails because two sides of the triangle, the luff and foot, will need to fit to get the sail on the mast and boom. The roach of the sail should be checked to make sure that it can pass the backstay.

2. Sheeting

The sheets are the principle means of controlling the trim of the sails with the aim of getting the telltales flying. Over-sheeting the headsail will flatten the sail to a shape that is no longer aerodynamically efficient and thus not producing the ideal amount of power. Not enough sheet tension will result in the draft of the headsail being too deep, so air will stall as it flows across it, again not producing the prescribed amount of power.

For the mainsail, the sheet is controlling the angle of attack of the sail via the boom but the same principles hold true as for the headsail: over-sheeting and under-sheeting will both mean that airflow across the sail is not optimised so the sail will not perform.

3. Sheet leads and car position

The sheet leads and car positions for headsails are crucial to trim. Moving the car forward or aft by just a few centimetres can drastically change the performance of a sail, particularly upwind. If the car is too far forward the foot and lower portion of the sail will be too full to allow the sail to be efficiently used upwind. If the car is too far aft the foot of the sail will probably be pulled tight but the head of the sail will twist open, again making for an inefficient sail shape. A good rule of thumb for this is that when fully sheeted on, the foot should be almost touching the chainplate or shroud and the leech should be almost touching the spreader tip. It is worth experimenting with car positions on different points of sail and marking the best positions for each point of sail on the track.

4. Correct halyard tension

Halyard tension is a significant factor controlling the trim and therefore the performance of a sail. Horizontal wrinkles in the sail when it is sheeted on will normally indicate that more halyard tension is required while vertical wrinkles before the sheet is tensioned indicate too much halyard tension which can damage the sail. The aim is to create a smooth surface for the breeze to blow over rather than a wrinkled surface that will arrest and disrupt the air flow across the sail. When moored, headsail halyards should be eased to avoid stretching the sail.

5. Batten tension

Batten tension is crucial to the flying shape of the sail because battens help form the aerodynamic shape of the sail. Battens that are too loose in their pockets will sit straight like slats in a venetian blind: they require compression to make them bend. Too much batten tension will result in too much bend which can make the draft of the sail too deep. Excessive batten tension may also make it hard work to hoist and drop a sail.

6. Leech lines

These are a much neglected feature of many sails — again correct tensioning is crucial to the performance of the sail. A slack leech line will not support the leech which will adversely affect the performance of the sail. A slack leech line will probably also lead to the leech flapping, and if left to do this for long periods will mean a trip to the sail loft for repairs. If the leech line is too tight, it will hook the back edge of the sail in upsetting the airflow across the sail and slow it down; it has a similar braking affect to an aeroplane putting its flaps up which will not help speed or helming. It is worth ensuring that a good-quality line made from spectra or similar is used for the leech line: venetian blind cord is too stretchy and will mean that it constantly needs to be tensioned and eased as the wind changes in strength.

7. The boomvang

The vang is used to control the twist towards the head of the mainsail. The vang works in conjunction with the mainsheet to provide downwards pressure on the boom, tensioning the leech. Twist can be desirable in some circumstances, for example when over-powered or in choppy conditions where acceleration is required, but in general terms it is better to reduce twist with the aim of having the top batten parallel with the boom. The vang is also very helpful when reaching because it stops the boom lifting which depowers the sail.

8. The traveller

This controls the angle of the mainsail to the wind and is useful for controlling the balance on the helm. Upwind, for maximum power, the boom should be on or very close to the centre line with the mainsheet running near vertically from block to boom. This will ensure that the angle of attack is optimised and twist in the head of the sail is minimised.

9. Mast shape

Mast shape is another variable that can affect the performance and trim of the sails. A mast needs to be set up properly initially to ensure that the right amount of pre-bend and rake are present. A badly tuned mast can mean that the sails will never trim properly, however much you tweak them. Once the mast has been set up, generally it can be forgotten until the next rig check or replacement of standing rigging or sails. Mast shape can be altered with backstay tension on some boats. Tightening the backstay will take sag out of the forestay which will control the depth and entry of the headsail. To get the best performance upwind forestay sag should be minimised, but off the wind, for maximum power, some sag can provide more power because the depth of the headsail will be increased. It is important to have a sail/mast combination that is suited to each other, otherwise accurate trim cannot be achieved.

10. Recutting

Taking your sails to a sail loft to get them recut is a more remedial measure that will ultimately improve the boat’s performance. Over time most sails built for cruising will stretch. This stretch will normally result in the draft of the sail moving aft of its original position which will mean that the flying shape of the sail is no longer aerodynamically efficient. Recutting should bring the sail back to its original shape, allowing it to work efficiently again.

Competitiveness

There are a few reasons to trim your sails so they perform as they were designed to. Another one not mentioned so far is the naturally competitiveness of human nature. Many cruisers will tell us that they are not interested in speed; so why is it then that when there are two cruising yachts close to each other, each boat tries to beat the other to the destination?