How to sail in light winds

Many years ago I voluntarily turned my back on the most powerful aid to light wind sailing known to man – when I gave up smoking. The world’s most high-tech wind indicators are crude and insensitive compared to the curling wisp of tobacco smoke. But you don’t have to doom yourself to life as a social outcast, to keep sailing when the wind drops. The techniques I’ll outline over the next few pages aren’t particularly racy: they’re as applicable to cruising couples as they are to anyone else.

When ghosting along in a breeze that barely ruffles the sea surface and only just fills your sails, it’s all too tempting to sit back and drift on until things kick in again. Don’t get me wrong – I’ve spent many a happy morning afloat watching the world go by, keeping an eye out in seamanlike manner, but remaining largely unconcerned about boatspeed or time of arrival. Such is the joy of cruising.

However, sometimes we need to keep the knots up when the wind starts to become light. Perhaps it’s simply that we’re loathe to break the silence with the engine. And keeping the boat moving in light airs can be fun, often using tricks and techniques we were taught as dinghy sailors.

Trying one or two of them may well mean that you can make port without reaching for the ignition.

1. Understand the sea breeze

I used to skipper a lovely old 56-footer for a Swiss owner. He was every bit as methodical and organised as you would expect anyone from his country to be, planning his summer cruises in meticulous detail. He even once sent me the summer itinerary along with his Christmas card. And if his plans, conceived in Zurich in winter, said that we’d be leaving Royan at 0730 on a particular morning in July, then 0730 was when he expected to leave, regardless of the weather or the tide.

One Biscay trip, in particular, was plagued by light winds.Every morning, we would leave early and drift for a few hours before switching on the engine to catch up with the owner’s ambitious schedule. After lunch, he would retire for his nap, leaving me and the crew to enjoy a cracking sail in the afternoon sea breeze!

The mechanisms that create local winds are many and varied. It’s worth buying a book – such as the RYA’s Weather Handbook – and reading up on them while you’re waiting for the wind to blow! But there are a number of fairly simple rules of thumb that apply to coastal winds:

Warm days

On warm days with light winds, from any direction, the wind within 5-10 miles of the coast will generally increase during the afternoon and die at dusk as the land heats and cools. Don’t rush breakfast – the sailing will almost always be better later on.

Spring and summer

In spring and summer, clear skies and a light offshore breeze at breakfast time are perfect conditions for a sea breeze. There will probably be a brief period of flat calm, but look out for puffy white cumulus clouds forming over the shore showing the beginning of the sea breeze circulation. The clouds will drift inland as the onshore sea breeze becomes established, and the sea breeze is likely to veer (shift clockwise) during the afternoon.

Sea breezes are strongest near the coast, but can be felt as much as 10 miles offshore.

2. Use the tide

When ghosting along in light airs, a knot or so of tide can make all the difference between making progress and going backwards. But although tide tables, tidal stream atlases and the tide prediction functions on most chartplotters look precise, they are all subject to errors caused by weather conditions and omissions caused by features too local to show up on small-scale maps.

On both sides of Portland Bill, for instance, the tidal streams flow south for nine hours out of every twelve. There’s a similar effect along the northern edge of the Cherbourg peninsula, where anyone prepared to hug the coast can gain a couple of hours of west-going tide. These two are well-known, but similar effects occur close to most headlands.

Compare your course and speed

Compare your course and speed over the ground (shown by your GPS) with your course and speed through the water (shown by your log and compass) to gauge the strength and direction of the
tidal stream.

Go as close inshore as you dare

Faced with a contrary tide, the general rule is to go in as close inshore as you dare. Even if you don’t pick up a back eddy or counter-current, the speed of the foul tide will be reduced in shallow water. When the tide is in your favour, of course, it pays to stay out in deeper water, where the tide flows faster.

3. Use the tidal wind

Tidal streams don’t just carry you in the direction they happen to be flowing – they also create apparent wind. Imagine that you are hanging on a mooring in no wind, with a four-knot tidal stream. You don’t feel any wind, but if you let go the mooring, and drift downstream at four knots, you will be moving through the mass of stationary air around you – so you will feel what appears to be a four-knot wind blowing against the tide.

You can’t use this tidal wind to make progress against the tide, but a four-knot Force 2 is enough to give you some control. Where you have a few knots of real wind blowing against the tide, the combination of the true wind and the tidal wind can easily add up to a pleasant sail.

If you are beating across the tidal stream, keep the tide on your lee bow to make the most of the tidal wind. On a cross-channel passage beating into a southerly wind, it would pay to be on starboard tack while the tide is flowing west, and tack onto port when the tide turns.

4. Look for catspaws

In very light and flukey conditions, the best anyone can really hope to achieve in the way of sail setting is to set everything up to suit where they think the next breath of wind will come from, and hope for the best.

Look for catspaws, patches of ripples on the water, perhaps only a few yards across. Catspaws heading towards you tell you that a puff is on its way, and their direction of movement is usually a good indication of its direction.

5. Use traditional navigation

Most chartplotters include tidal data, but very few of them are able to apply it to work out the optimum course to steer.

At low speeds, it’s doubly important to ‘shape a course’ using traditional chartwork or the ‘one in sixty rule’, and to avoid ending up down-tide of your destination.

The one in sixty rule is a fairly straightforward piece of simple arithmetic that says:

Tide speed x 60 ÷ Boat speed  = course correction

So if you are sailing at five knots across a two-knot tidal stream, you will need to steer

2 x 60 ÷ 5 = 24° up-tide

When the tidal stream is changing, as it would on a longer passage, you need to add up all the tidal streams in one direction, take away all the tidal streams in the other direction, and divide by the total time to find an average.

If, for instance, you expect to be pushed 11.5 miles west and 6.5 miles east during a 15-hour south-bound passage, the average tidal effect is going to be 11.5 – 6.5 = 5.0 miles, so the average is going to be 5 ÷ 15 = 0.33 knots west-going.

If the expected boat speed is 4 knots, the offset will be:

0.33 x 60 ÷ 4 = 5°

So you will need to steer 5° east (up-tide) of the straight-line route to your destination.

6. Use lightweight sheets

A 15sqm jib in a full 40-knot gale creates a sheet load of around half a tonne, so even in a real blow, sheets of 8mm braided polyester would be well up to the job.

The only reason most of us use thicker sheets is simply for comfort – a 14mm or 16mm rope grips the winch better and is much nicer to handle!

But in light airs such massively oversized sheets become a liability. Their sheer weight robs us of control by pulling our sails in towards the boat, and easing sheets defeats its own purpose by adding more weight to the bight of rope pulling the sails towards the centreline.

So think about having a set of 6mm or 8mm genoa sheets ready for when the wind falls light. They don’t need to be the finest quality yacht ropes – even a hank of polypropylene from B&Q will be fine (although if you do choose to use polypropylene, bear in mind that it’s prone to tangle).

Changing the mainsheet may not be quite as simple, but it’s usually possible to achieve a similar effect by unreeving it from the blocks.

7. Carry a lightweight headsail

As well as lightweight sheets, racing crews often carry a sail called a ‘drifter’. This is a very lightweight spinnaker that they’ll use on any point of sail from a close reach to a run in a Force 1–2.

Cruisers used to buy tired racing spinnakers, or hang on to an ancient No1 genoa, for this very purpose. Some still carry a drifter, considering it a piece of safety kit for when the breeze drops at the wrong moment.

8. Reduce your drag

Naval architects will talk about at least five different kinds of drag, or resistance. They can’t be eliminated, but it makes sense to reduce them as much as possible.

Wavemaking drag is the big one. It imposes a natural speed limit of about 1.3 x √LWL (waterline length)and is the reason why big boats generally sail faster than small ones, and why performance-minded designers try to give their boats the longest waterlines they can. But at speeds below about five knots, waterline length isn’t really an issue: we can afford to sacrifice length in favour of lifting the wide aft sections of the boat out of the water. Moving weight forward reduces the wetted surface, and therefore skin friction, and it reduces turbulence at the stern to reduce what is sometimes called ‘wavebreaking drag’ or ‘form drag’.

Appendage drag is exactly what its name suggests: it’s the drag caused by appendages such as propellers and rudders. There’s not much you can do to reduce it, but you can certainly increase it by using lots of rudder. So in light airs, it’s vital to use as little rudder as possible, especially when making big alterations of course. ‘Tiller waggling’ might work for Optimists and Lasers, but it does nothing for a cruising yacht!

We can learn something else from dinghy sailing here – keep crew movement to a minimum. In yachts under about 30ft, people shifting their weight will have an effect on the flow of water around the keel and will inevitably slow you down.

9. Adjust the boat’s angle of heel

In light winds, we’ve all seen race crews sitting on the leeward rail, sometimes moving sails and other kit around the deck. What they’re doing is heeling the yacht so that the sails fall into something like an aerofoil shape, ready to take advantage of a puff that may only last a few seconds. A short-handed cruising crew may have less effect on the heel of the boat, but can still be a huge help. And if you think the idea sounds a bit racy, remember you often find shade behind the sails and get to dangle your feet in the water!

10. Set the genoa for light airs

On most cruising boats, the genoa is the main driving sail, so the primary objective is to ensure you are using the power of the headsail to drive the boat forwards rather than sideways.

Without the weight of wind stretching the sail, sheet, and halyard, it’s very easy to over-tension everything – flattening the sail and reducing the sheeting angle. It may allow you to point higher, but at the expense of your boatspeed. It’s exactly what we don’t want in light airs.

So start by easing the halyard until it is only just tight enough to remove horizontal or star-shaped wrinkles at the luff.

Ease the sheet, too: when beating in light airs, try to keep the leech of the sail the same distance off the spreaders as it is when you are beating in normal conditions.

Next, look at the telltales. The lower ones – the ‘steering’ tell-tales, used to steer the boat when beating, or to adjust the sheet when off the wind – should both be streaming aft, more or less horizontal and in line with each other for at least 50% of the time. If they aren’t, adjust either the sheet or your course until they are.

The upper tell-tales – the ‘twist’ tell-tales, used to adjust the shape of the sail – should be behaving in almost exactly the same way as the lower ones, but the chances are that they won’t be. That’s because there’s always a difference between the wind direction at deck level and its direction at masthead height. The deck level wind is always slightly ahead of the masthead wind, but the difference is particularly pronounced in light airs, so the sail needs more twist in light winds to match the more twisted airflow.

Unfortunately, the natural stretchiness of sails and ropes tends to reduce the twist in lightly loaded sails, rather than increasing it, but we can overcome this by moving the genoa sheet fairlead aft to relax the tension in the leech.

The objective is to get all the luff tell-tales to ‘break’ at the same time. If the bottom tell-tales droop first, move the fairlead aft to increase the twist. If the top tell-tales droop first, the sail has too much twist, and the fairlead needs to be moved forward.

11. Set the mainsail for light airs

Similar principles apply to the mainsail, except that it’s very easy to overdo the rule of thumb that says ‘slacken everything’ in light winds.

Slow-moving air is more likely to flow smoothly across a flat sail than one that’s too full, so although it’s a good idea to remove vertical folds by using soft battens and leaving the Cunningham and leech line slack, any other tweaks should be aimed at getting the twist right, rather than increasing the fullness of a sail that is probably already baggy from a few seasons’ cruising!

A good starting point is to look up at the top batten from under the windward side of the boom. Regardless of the wind strength, the aft section of the batten should be parallel to the boom, or angled slightly downwind of it.

If the end of the batten is poking up to windward, the leech is too tight, so ease the kicker, and move the mainsheet traveller to the centreline or even to windward.

If you have tell-tales along the leech you can fine-tune the twist even more. Like their counterparts on the luff of the genoa, the idea is to make sure the sail is sheeted correctly by getting the bottom tell-tale streaming aft for at least 50% of the time, and then use the kicker and mainsheet traveller to adjust the sail twist so that the top tell-tale is doing the same.