How to sail

This sounds like it’s going to be a big section, but really there’s not that much to it. It’s easy to make a sailing boat sail: you just pull the strings and off it goes. The trick is knowing which ones to pull, when, and how hard.

Everything you can say about sailing has two sections to it – when sailing with the wind ahead of the beam and when the wind is aft of the beam. This is because, in a fore-and-aft rigged boat (like almost all modern yachts) there are two modes of operation of the sails. They can either be acting as aerofoils in a laminar flow of air (wind ahead of the beam) or they can be acting as wind-jammers, stalled and mostly just catching the wind and turning it into turbulence (wind aft). Somewhere around a beam reach, the boom is so far out that it comes in contact with the shrouds, won’t go out any further, and there is a transition from one mode to the other if the wind continues to back aft.

Wind ahead of the beam

When the sails are acting as aerofoils, the simplest rule for trimming them is to start with the fore-most sail on the boat and pull in the sheet until the luff just fills and goes quiet. If it’s already full and quiet, then let it out slightly until the sail just luffs and then pull it in again, just enough, as above. Work your way aft doing the same with each sail and you are then making the best possible progress on this course. If you want to prove that, head the boat up slightly into the wind and, within a few degrees, both or all three sails should begin to luff at the same time, most of their way up their height, together.

Why do I say ‘both or all three’? Many cruising yachts were designed to fly more than just a main and a jib. This is because designers considered keeping the size of each individual sail down to something that is manageable by one person on deck in a gale. They also wanted to keep mast height down, to make oversized standing rigging more feasible for the height supported. Modern ‘cruiser-racer’ designs do not always follow these considerations, as there is no doubt that each extra luff, let alone extra mast, presents considerable windage that reduces the up-wind efficiency of the rig. Roller reefing foresails and in-mast furling mainsails (or lazyjacks and self-stowing mains) are also meant to reduce the effort involved in handling big sails, although I don’t really like these things – they add to the weight and clutter aloft and can jam up terribly when you really don’t want them to. Rusalka Mist is a cutter, which means she has a jib at the bow, a staysail that attaches aft on the foredeck, and a mainsail. There are many cruising ketches around that have a jib, a main and a mizzen mast for the third sail.

Every sail works by deflecting the air, and that is why I suggested starting with trimming the fore-most sail – it is slicing into clean air. Every sail behind it is slicing into air that has already been deflected by the sail(s) in front. When all your sails are trimmed, you should see that each one’s sheet is hardened in a little more than the one in front of it. This is correct, and is another factor that limits the upwind performance of a three-sailed boat – at some point the aft-most sail becomes so hardened in that it effectively prevents you pointing higher into the wind than if it wasn’t there.

Sail twist

I mentioned above that, when luffing, each sail should luff uniformly up its height. This is slightly unrealistic as no sail is cut so perfectly, but if it is clear that a sail luffs at the bottom way before the top, or vice versa, then the sail twist can be adjusted.

For a foresail, changing the sheeting angle by moving the sheeting car will do this. Move it forward to pull in the top of the sail relative to the bottom, and aft for the opposite effect. On the mainsail, once the boom angle is set, pulling down on the boom will reduce sail twist and letting it up increases it. You can adjust the downforce on the boom either with the kicking strap or by changing the sheeting angle by moving the mainsheet car. Putting the sheet car under the boom increases the downforce, putting it away to windward reduces the downforce.

Some sail twist is usually required and the reason is that the boat is sailing in a relative wind, created by a combination of the actual wind and a wind effectively generated by the boat’s motion. Now, the real wind is all blowing in the same direction, but there is usually a noticeable speed-gradient in it, with the wind nearest the water going a little slower than the wind at mast-top height, due the drag on the water slowing it down. The wind generated by the boat’s motion is in a different direction and has no such gradient – the deck is going at exactly the same speed as the mast-top. When you combine these two ‘vector fields’ you end up with an apparent wind that is slightly more on the bow at deck-height than it is at the masthead. That’s why we need a little twist in each sail, to make the most of each part of the wind gradient. The top of the sail is held slightly further off the wind than the bottom. Exactly how much can only be found by trial and error. When the sail luffs all the way up at the same time, or at least in the middle, we have it right.

Sail shape

When sailing upwind, it is important to have the luffs of the sails tight. Any flapping or bellying of the luff will make the sail much less efficient. But there is slightly more to it than that. Sails are not flat pieces of cloth, and they are not cut with their threads parallel with the luff either. The sail has a three-dimensional shape, that can be altered by tightening or slightly easing the halyard, to stretch or relax the cloth in the luff.

Looking up, you can see the curvature of the sail along each fore and aft line. Some sails even have dark tapes sewn into them to make this curve more apparent from below. Where is the point of maximum curvature? We do not want to see the front half of the sail only gently curved with the maximum curvature aft of the centreline and the last bit of sail hooked around. If this is the case, get a winch handle and tighten the luff, stretch the cloth ‘on the bias’ and pull that point of maximum curvature forward, at least to the centre of the sail and preferably to a point about one third from the front of the sail. It may be necessary to de-power the sail by releasing the sheet until the luff shakes free, or by rounding up into the wind, to do this in any kind of breeze.

Now, how deep is that belly? If it is too deep and baggy on the mainsail, you may be able to tighten the outhaul on the boom to flatten things out. Generally speaking, the stronger the wind, the flatter you want your sails; you can afford to have them bag in a gentle zephyr, but that will make you heel too much and slow you down in a blow. Think Wright-brother wings or fighter-jet wings depending on the conditions. Racing sailors will also tighten the standing rigging to bend the mast to reduce this bagginess on their craft. Hopefully your long-distance cruising mast is way too stiff for you to do this, and hopefully no-one has rigged you any lines to try it with either. In the end, too much bag, in main or foresails, might mean that the sails have reached the end of their life and it’s time to fork out on new ones. I recently reached this point in this, Rusalka‘s twentieth year afloat, and I can vouch for the better shape in new sails than in twenty-year-old ones. That’s not to say the old ones didn’t work, of course, but there comes a time…

The last adjustment for sail shape is the leech-cords. These come into use if you hear a steady machine-gun noise from a sail that turns out to be caused by the leech (the trailing edge) fluttering in the wind even though everything else is right. A gentle pull on the cord should stop this, give everybody some peace and stop that flutter from slowing the boat down with a steady stream of turbulence being left behind. Over-tensioning these cords will cause the leech of the sail to ‘hook’ which severely disrupts the airflow as it leaves the sail and should be avoided. Again, just tight enough and no more.


Sailing into or across the wind with too much sail up leads to too much heel. There is never any point in sailing at more than about 20 degrees of heel. If you don’t have an inclinometer built into the compass, then fit a separate one, they’re very cheap and simple. I fitted one down below anyway, as that is where I spend most of my time these days when under sail (more on such tactics in another article). If you have just spent the last few weeks living aboard, seeing your whole home tilt at even 10 degrees can be alarming at first, so it’s worth having a impartial gauge to consult when in doubt.

Learning when to reef the sails was one of the biggest single step-changes I made during my early sailing adventures. (Learning to follow transits was another, but that goes elsewhere too.) “The time to put in a reef is when you first think about it. If you’re thinking of taking one out, have a cup of tea first,” I was told by some instructional video that I had at the time.

A boat with too much sail up heels over too far for comfort or for safety when walking about on deck or down below. Heeling also increases weather helm, which reduces your ability to manoeuvre, or even to maintain the course you want. Not only that, but the increased rudder angle under water increases drag and slows the boat down. The sails, when the mast is angled over too far, present less effective area to the wind and so also become less efficient, which slows the boat down. The increased white water and sense of urgency on deck is caused less by increased speed and is more due to pushing wrong-shaped parts of the hull under water and by dragging a deeply angled and inefficient keel sideways with the increased leeway.

Put your harness on, clip on securely and get up there. Put a reef in the main; change to a smaller jib; if you have three or more sails, lower one altogether. The peace and calm will astound you. Life can resume. Then check the GPS – you’re probably going no slower and may even be making a better VMG towards your waypoint than you were before. And you can think; and you feel in control again; and you can put the kettle on too, and maybe make a sandwich.

Notice I didn’t say, roll some of the main away and roll up half the jib. These two actions, if possible, will also destroy your sail shapes and lead to only a fraction of the improvements that could have been gained from what I suggested. Understanding this may lead to saving you a lot of money, or to you regretting having spent it as you convert your rig back to more traditional lines.

It is possible to reduce sail too much. Look at the bow of your boat, look at the mast and all its rigging. All of this is exposed to the wind too. Expecting a postage-stamp of sail to pull all that windage upwind off a lee shore on a stormy night is unrealistic. Sailing at 15 to 20 degrees of heel will not hurt you or the boat and is sometimes just the thing to do. Even sailing with the side decks under, heeling 30 or 40 degrees, won’t hurt the boat. Just be aware that it’s never necessary, but don’t panic if it happens. Clip on, adjust the sails, alter the course or reef and reduce sail and all will be well. Those tonnes of lead in the keel will bring you back up – never let yourself or any of your crew worry that, ‘We’re going to tip over!’ – it’s not like that. Not in a fully decked, well-found and properly ballasted yacht.

Wind aft of the beam

If the wind is aft of the beam, the sails are stalled and do not need careful trimming. There are a few things to look out for, though. The most important issue is safety from an unexpected gybe. If the boom comes across the boat and somebody is hit by it, or by any part of the mainsheet, they can be killed. Simple as that. If it comes across hard enough, it can bring down the mast too. In any blow with some part of the passage possibly off the wind, I always rig preventers before leaving. There are several designs of boom brakes and other gizmoes, but I haven’t seen anything better than the simplest approach.

If the main does get back-winded with a preventer rigged, you will want the preventer to have maximum possible mechanical advantage to prevent damage to the boom and to allow you the strength to sort it out safely. So, there is no point in attaching anything to the middle of the boom, you want a line running forward from the boom end. I say forward as, in the interests of mechanical advantage, there is no point in this line attaching amidships or anywhere near the mast (the pivot point). I have two hefty U-bolts on the foredeck that hold the forward ends of the jackstays, and that I can also clip my harness onto directly when I’m up there at sea. To begin with, I used to pass the preventers through these and lead them back along the sidedecks to the cockpit. Nowadays I have splashed out on a pair of snatch-blocks and attach these to the U-bolts first to reduce friction on the lines. With preventers rigged, you can relax as the boat rolls and the wind dies too.

There is a limit to how far you want to let out the foresails too. The rule I use is never to let out the sheet so that the sail leaves the stay headed in a forward direction. The luff of the sail should be at right angles to the centreline, no more. The reason for this is that I once read about the mechanics of a ‘rolling engine’ that you can establish with the top part of the sail sagging off forward. As the boat rolls to windward, the top of the sail un-stalls, becomes laminar and efficient and reduces the pull to leeward. At the peak of the roll it stalls again and the extra drag pulls you back into the roll to leeward. Something like that. I don’t know if its true, but we roll badly enough on a broad reach in a blow that I’ve never wanted to find out. Right-angled luffs are good enough for me as they look effective too. Sail twist in the main can lead to the same effect at the top and tension in the kicking strap pulls everything back into shape there too.

Specialist sails

I have a whisker pole and have occasionally poled out the genoa. I use a downhaul to the foredeck to keep it under control. We also have a MPS or cruising chute, a ‘nylon diesel’, that I have used in the English Channel, but it was never needed further afield. People in the past have sworn by ‘twins’, two matching jibs hoisted on the same stay and poled out in opposite directions. I have never tried them, but the theory is good. I made sure that the new rolling furling foil for the jib had two slots just in case I ever do. While in Santa Cruz de Tenerife we watched another yacht in the harbour testing the hoisting and rigging of a square sail and yard in preparation for their trade wind Atlantic crossing. It looked rather large to me, but I never heard from them to find out how it went.

Specialist downwind sails including spinnakers and square sails usually work in a slightly different way to stalled fore-and-aft sails off the wind. They can act in a laminar-flow, non-stalled way with the top edge(s) acting as leading edge(s) and significant airflow down the sail from top to bottom. This provides vertical lift as well as drive. The vertical lift keeps the bow from digging in and the lack of turbulence due to not being stalled can reduce rolling and other unpredictable behaviours.


With the wind fair a man is master of his boat and has the power to drive her as hard as he wishes – even to the point of destruction. In a contrary wind a well found yacht is master. She has more stamina to windward than any man by himself…

So wrote Frank Mulville in his excellent book Single-handed Sailing in 1981. While on the wind we look at the inclinometer to decide when to reduce sail; off the wind we look at the log. The speed of the boat must be kept under control. For Rusalka, I limit the downwind speed at six knots, but the figure depends on waterline length, sea conditions, wind strength and self-steering efficiency. Too fast and you put excess stress on the steering gear and the rudder can end up biting into nothing but foam.

Reducing sail downwind in a blow can be problematic. If the sails cannot be pulled down on the downwind course, due to friction in the mast track or problems on the foredeck, then rounding up by passing beam-on through heavy seas can be quite daunting. Nothing beats getting a good forecast of wind to come and getting the sails down or reefed before the forces build up. This is where earlier comments about smaller sails on cruising boats begin to make more sense.

Sailing slowly

Another problem a lot of cruising converts have is in learning when and how not to sail at the maximum capability of the boat and the rig. Most of my comments above have been about tweaking the sails for maximum effectiveness, but that is where most tutorials end with no mention of how to slow down for the night, in the harbour, when sailing up to a buoy, or to a man overboard.

Practicing manoeuvres under sail, when there is no need to, is good practice. You never know when the engine will fail, a rope or net will foul the prop or some other need may arise. Being familiar with how your boat behaves under sail is invaluable when you need it. It’s so satisfying too. In harbour, I usually have the engine ticking over out of gear anyway while I’m messing around under sail, just in case I misjudge something or the unexpected arrives around the pierhead.

Reducing sail is the obvious way to reduce speed. Significant speed reductions need significant changes, so whole sails come down on the way into harbour. Rusalka will handle on most points of sail under just the staysail, as it is near enough to midships, but this is relatively unusual. There is nothing to stop you putting a second or third reef into the main and rolling up two thirds of the jib to come slowly into a bay or a harbour to anchor. If you’re going to want to tack efficiently up wind, then maybe changing to a storm jib in good time is worth the effort before getting into confined waters.

There are other ways quickly and temporarily to slow a boat down under sail. Letting the jib sheets fly is well known but can lead to turning a big sail into a huge unruly flag with the downwind drag on the bow still significant. Slackening the sheets to spill wind is OK when manoeuvring, but is no substitute for reducing sail as a long-term response to a rising wind. The old gaffers used to ‘scandalise the main’ to reduce its drive. We can do something similar by slackening the kicking strap and mainsheet right off and pulling in several yards of topping lift. With the boom right up in the air, there is very little drive from the mainsail, even downwind. Mainsail drive can be reinstated in a moment just by dropping the boom again, which would not be so easy if the main had been dropped onto the deck.

With a reef or two in the main, even on a big yacht (36 – 40 ft) the main sheet can be man-handled in one piece just like a dinghy or windsurfer. This is useful when manoeuvring slowly up to a mark.

Don’t try to sail too close to the wind when underpowered or using makeshift slow rigs – 50 degrees off the wind will work, anything less may not. Keep enough speed to keep control via the rudder.

When sailing the open sea with no one on deck, even more so at night, it is impossible to say that there is not some floating tree or shipping container lurking in front, or a sleeping whale. The best defence against these possibilities is not to spend all night gripping the tiller and staring into the blackness, but to sail slowly. Hitting a steel shipping container at 4 knots will do a lot less damage than hitting it at 7 knots. The time to race is in the bay with all your friends around, not in the middle of nowhere, in the middle of the night with no one for hundreds of miles to come and help you. Take it easy.


One Response to “How to sail”

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