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Sailing in waves: top tips to keep you safe at speed

Sailing in waves can be difficult, we find out about the best rough weather tactics to keep you sailing for speed, comfort, safety and enjoyment

Sailing in waves can make for a jarring, juddering experience and long, uncomfortable passages and at worst, a dangerous, boat-rolling hazard. However, it can also mean a thrilling surfing ride to your destination.

Understanding how to set up your boat for sailing in waves, to take advantage of them or ameliorate their worst traits is a skill that it is well worth understanding and practising in order to make your sailing more enjoyable, and to give you the confidence to sail in a wider range of conditions.

Sailing in waves downwind

‘Fairly obviously, the bigger the boat you sail the less of a problem waves generally are,’ say Merfyn Owen of Owen Clark Yacht Design, himself a double Cape Horner and former BT Global Challenge skipper with over 250,000 miles under his belt.

‘To take that to an extreme, if you think about an oil tanker in the middle of an ocean, a wave that would barely wet the deck for her would be something big enough to roll a cruising yacht.

‘It’s really all about the wave energy transfer and the object that the energy is being transferred through, in this case, the boat. So although size is key, when sailing with waves, speed is very much your friend, too, as the energy transfer will be reduced when you are travelling at pace.’

The ‘speed is your friend’ attitude can be difficult to get your head around. Typically it feels counterintuitive when sailing in big waves to want to speed up. Usually in these sort of extreme conditions, slower tends to feel safer but it is something we should all be trying to do in a following sea, to reduce the chance of broaching or being rolled.

‘If you take a fairly modern boat, they all tend to be easier to sail downwind in big waves for a couple of reasons, but one of the key reasons is that they are able to achieve higher sustained speeds downwind,’ says Neil Mackley of North Sails.

‘These days double digits downwind are not uncommon and even high teens are fairly regularly seen. You don’t have to go back too many years before 8 knots was the maximum many boats would be likely to see.’

The faster you sail downwind in waves, though, the more technique is required to reach your destination safely.

There are several factors at play here. Firstly, sailing at higher speeds when surfing down a wave gives your rudder movement greater impact in terms of direction change. Thus when surfing down a big wave, the boat accelerates and it is easy to oversteer and end up with big changes in direction, which also cause big changes in wind angle – a light touch is what is needed with small steering inputs.

The second factor is around choosing your angle down a wave to ensure you are heading in the right direction when you reach the troughs.

It’s not called surfing a wave for nothing, and it helps to think about how actual surfers make their way down a wave, never straight down the face, always at a perpendicular angle to the wave direction.

Sea state

Photo: OnEdition

Just as the stern begins to lift, accelerate the boat by luffing to a reach. The bigger and faster the wave, the earlier and more extreme an angle change is required to get your boat speed close to that of the wave.

Once surfing, don’t steer straight down the wave: you’ll hit the one in front. If you stop, the wave will roll past and, significantly, your apparent wind angle will suddenly change.

Instead, turn so the boat slides along the face of the wave, upwind or downwind of the wave perpendicular; this extends the time surfing but also keeps the boat at a constant speed.

‘When the wave hits, something has to happen to that energy, which is a function of the wave’s weight and speed. The energy is transferred into the vessel and if the vessel is going relatively slowly and is relatively small then there is sufficient energy in the wave to roll the boat over,’ says Owen.

‘If a 36-footer that weighs 6-7 tonnes and is travelling downwind at 6-7 knots is hit by a wave that is travelling at 30 knots, it is going to be far more impacted than a 6-7 tonne trimaran going at 25 knots.

Understanding the motion of water in waves is key to understanding how best to sail through or with them

‘When the 30-knot wave hits, its relative velocity is 5 knots compared to 24 knots for the boat going at 6 knots. So all that energy and mass hits the boat and the result is that a certain percentage of that energy is transferred into the boat, which subsequently creates the roll. So the faster you can be going at the moment the wave hits, the better.’

Most of us do not sail in a multihull capable of making 20 knots downwind, but the point remains that the faster you can travel the better in terms of energy transfer.

Similarly, if the waves are not big enough to induce surfing or your boat is quite heavy and does not surf regularly down the face of the wave, the technique remains broadly the same.

The main difference when not surfing down waves are that the waves will be overtaking you so you are less likely to come to a stop sailing into the back of the next wave.

Nevertheless, the wave will still accelerate your boat and it is wise to head up just before the wave picks you up to increase speed and reduce the difference between the relative speeds of both wave and boat.

Rolling when sailing in waves

Steering down waves as above assumes the wave and wind direction are matched, allowing you to luff onto a broad reach on either gybe to ensure you are not sailing straight down the wave face.

There are, of course many situations in which you will encounter waves that are not in the same direction as the wind, so on one gybe it will be okay and on another it will be harder.

‘To some extent it is wise to think about taking the favoured gybe until the tide turns and the seastate reduces,’ says Owen. ‘There might be other factors, too; you may be able to get closer to the shore on the favoured gybe. Essentially, you should try to limit the time on the unfavoured gybe where possible and maximise time on the easier – and faster – gybe.’

Of course there are times when sailing in waves that they are going to roll the boat around and this is unavoidable, and it’s all but impossible to pick the perfect angle.

‘I think the biggest issue that a lot of people fear is the old death roll,’ comments Mackley. ‘That is a particular issue on older boats with a relatively wide beam but a narrow transom – they really tend to rock and roll all over the place.’

Rolling in waves is a big fear for many. Tightening the leech on your mainsail with your kicker will help, so will tightening the leech on your spinnaker with a tweaker line

The rolling Mackley mentions is born of a number of factors. In the simplest terms, a wider aft section provides more power downwind and enables the boat to sail faster. However, the effect can also be the result of the underwater shape of the boat reducing form stability.

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Ultimately it varies from hull shape to hull shape but as a rule, the wider-sterned modern cruisers tend to roll less.

‘There are things you can do to limit that roll, though, and at least provide a slightly less stressful experience. Broadly speaking you will want to sail with less twist in your sails, which helps reduce the rolling motion.

‘Essentially what is happening is if you have a quite open leech, the air escapes off the very top portion of the mainsail. So if you have a lot of twist in the mainsail then the sail at the top ends up being something like 90 ̊ off the centerline. Whereas the bottom of the main with the boom out will be much less than 90 ̊ to the centreline and so be holding power down low. It is the difference in the angle between those that induces rolling in the boat.

‘The top of the sail will spill wind, which allows the masthead to roll to windward and then the keel takes over and rolls you back upright and the whole thing just gets worse and worse. So applying leech tension via the kicking strap will give a more even leech profile and allow the wind to stay attached through the whole length of the leech.

‘With a spinnaker up, the same thing is true, but with the added difficulty that you have a soft leech and luff. The aim is to try and stop the spinnaker rotating round the front of the boat.’

Mackley says that this can be done in a number of ways. Firstly having a ‘tweaker’ line on the sheet is useful. Typically this is a block or ring that allows the sheet to run freely through it, which then runs down to another block on the toerail and to a cleat.

This acts to pull down on the spinnaker sheet but lets the sheet run through it and controls the amount of twist that develops in the leech of the spinnaker.

The result of pulling this on is to stop the leeward side of the spinnaker from rotating round the forestay. ‘There is also a tendency for some people to allow the spinnaker pole to be too far forward, which also allows the top of the spinnaker to float to windward, which also induces the roll,’ Mackley adds.

Sailing in waves downwind in light weather

Although not as intimidating as windier weather, sailing downwind with a following swell can be just as hard.

As a general rule, the difficulty in very light weather is that the swell in effect kills wind. As you accelerate down a big swell, quite often you will see the apparent wind switch from being behind you to in front of you as you overtake the wind.

Speed differences in this situation are fairly small. If there is a 5-knot true wind speed and you are sailing at 3 knots, a significant swell will easily accelerate the boat to 5 knots, at which point you are essentially sailing in 0 knots of wind.

Even though it is not necessary to sail down the face of the wave at an angle to prevent sailing into the next wave in lighter winds, as the waves will typically be moving faster than you are, it is still worth considering sailing more of a reaching angle to increase boat speed and so reduce the difference between apparent wind when sailing down the face of the wave and the true wind speed when not.

In lighter weather you are likely to experience the problem of the mainsail unloading as the boat accelerates down a wave. Using a preventer on the boom can easily solve this, but it is not uncommon to see a boat accelerating down the face of a wave, overtaking the wind at which point the mainsail backs and acts as a large air brake.

This is not going to do any great damage but it is going to slow you down quite a lot and it is better to either let the mainsail flop around a bit or find a faster angle, even if it is a longer route to your destination as you will likely get there quicker.

Sailing in waves upwind

Sailing into a heavy seaway, or even a moderate chop can significantly reduce your speed, pointing ability and comfort. As such, simply sailing into a seaway can make your journey less comfortable and much longer – a double whammy of discomfort.

But if your course to steer is upwind and into a seaway, what can we do without resorting to the engine?

To some extent the answer is condition-dependent, but the basics of wave sailing remain the same. The water in a wave moves in a circular motion: downwind at the top, upwind at the bottom. The essence of sailing over waves is all about ensuring you use the energy locked into the wave to your advantage.

It is for this reason the advice has always been to luff as you climb the face and bear off slightly over the back of the wave. The aim here is to ensure you spend as little time as possible in the peak by luffing, and then bearing away to keep reasonable way on and keep you sailing in a broadly straight line.

Additionally, as you slow down up the wave, the apparent wind moves aft, allowing you to luff further, while as you accelerate down the back of the wave the apparent wind moves forward.

The problem here, though, is the additional steering makes sail trim difficult to master. In flatter water, we can set sails up for the conditions and steer a straight course, safe in the knowledge that barring some significant change in the wind strength or direction the boat will be set up correctly.

‘When it is very windy and you are sailing in big waves it can be very difficult,’ says Mackley. ‘With the sails sheeted on there is not much space to luff and bear away.

‘If you have too much sail area then you get locked into sailing the boat in a very high mode and slowing each time a wave hits, as every time you try to bear away at the top of the wave you are overpowered.’

The trick in these conditions is to give yourself a sail set-up which offers the best power over a wide range of angles. Not only does steering over a wave change your angle to the wind, but the apparent wind will also be moving around a lot too. When you are in the trough and going quite slowly, then the apparent windspeed will be much lower. As you bear off over the peak of the wave, the apparent will be noticeably higher.

‘You should think about reefing earlier than you would normally when sailing in big waves upwind,’ says Owen. ‘When the waves are really big, as well as a difference in apparent wind speed, you will also get a lull in the trough and a gust at the peak, so setting the boat up for the maximum wind strength you are going to experience is important.’ Mackley agrees, explaining that if you normally would reef in 19-20 knots upwind, then in a big seaway you will probably want to put a reef in at 16-17 knots to allow you to drive the boat properly.

‘Sailing with more twisted sails is also key in the windier wavy conditions,’ says Mackley. ‘You might not need to reef, but you will certainly want to sail with a lot more twist in the mainsail and headsail.

‘Essentially what you are trying to do is give yourself a wider groove to sail in, so with a lot more twist in your sails you are able to keep the sail trim right for a higher percentage of the time.’

On a race boat, the trimmers will be focused on the bow and trimming on as it lifts and the boat starts to luff up the face of the wave and then easing the sheets slightly as the helm bears off over the back of the wave.

Plenty of twist in your sails will help with the apparent wind direction changes that occur in big waves, particularly upwind

By putting twist into the sails when cruising we allow for the sails to still be delivering some power through the course of steering without becoming overpowered at the peak and underpowered in the troughs.

‘It is worth remembering that this applies to all your sails. Particularly for boats with a large headsail it is well worth putting twist into the headsail by moving the headsail cars back. It’s often not something people do but it will make a huge difference to keeping the boat evenly powered through the waves and so keeping the boat moving and preventing the situation where she is heeling then sitting upright and then heeling again over and over.’

Sailing in waves upwind in the light

Depending on the speed of the waves, your boat, and its manoeuvrability, there is always a lower limit where it is simply not possible to steer around the waves in the way described above.  The waves just shake the boat and rig around; the rig stalls; and the boat bounces up and down, going nowhere.

When the waves are not regular there are always high and low spots. Your focus needs to be on the water half a boat length or so in front of the bow. Steer for the obvious low spots as they appear and avoid the biggest highs: the larger the differences between highs and lows, the further it will be worth deviating from the mean course to minimise the effect of this obstacle course.

If there are no obvious high spots and low spots, sail freer and faster through the worst bits: your speed will at least ensure that the rig and foils are working, whereas trying to sail high and slowly will stall both and contribute to a slide to leeward.

To allow the boat to make good progress through the waves in light winds, we need to generate as much power as possible from the rig.

‘Trying to generate power in light winds and waves, means you are typically sailing with the sheet more eased and a lower mean angle,’ say Mackley. ‘You are not looking for the ultimate in terms of pointing but you are just trying to get the boat powered up and punching through the waves.

‘So you usually ease the sheet a few inches and sail with slightly less tension in the backstay to induce a little more power through headstay sag, which makes a fuller, more powerful sail.

‘You are generally trying to keep your sheeting angle a bit wider and more forgiving. As with windy sailing in waves, you are aiming for a forgiving sail set-up. We are not looking for absolute maximum upwind speed, you are more looking for the maximum forward speed all the time.’

Sailing in waves in extreme conditions

‘Upwind, even in severe waves, it is often okay as long as you can keep enough way on to continue to travel forwards. You will need to foot off quite a bit with very reduced sail but downwind, when a wave gets to a certain size it can be difficult,’ says Owen.

‘I’ve said that speed is your friend and that is certainly the case, but there is a point that you reach where you are going too fast and a broach, or worst a Chinese gybe becomes a very real possibility.

‘I would argue that slowing down is still not the right answer. Given what we know about how likely a wave travelling at speed is to roll a boat travelling at low speed then really you are just choosing the lesser of two evils by sailing quickly, and still reducing your likelihood of being rolled, even if
that likelihood is quite high.

The key to sailing upwind in big waves is to make sure you keep enough way on to make progress

‘If you look at fast racing boats these days, they very rarely carry a drogue or similar. It’s not that it wouldn’t work, it’s just that you never have to use it because you have sufficient speed to be okay.

‘So on a boat like that, there is no condition that would ever warrant the need to use one. You are far better off just sailing through it and keeping the boat moving.’

There is always a moment when we need to consider backing out. For those on passage, hopefully you will have identified some ports you can retreat to in your standard passage planning.

If you find that you are struggling to make decent headway upwind in rough conditions, it could well be worth firing up the motor to help drive the boat up a wave face, preventing the keel and rudder from stalling, so you maintain control and avoid punitive leeway. Or perhaps you need to drop the sails altogether.

Usually, if you’re struggling to make decent headway, you can make rapid progress downwind, so identify your nearest safe port (hopefully one that is easy to get into and has sufficient depth) that is downwind of your location and head there.

When to use the motor in waves

When sailing in waves upwind, motorsailing will often help you get to your destination quicker. However, sailing in waves downwind, motorsailing is not usually a useful option as you will, often, be sailing faster than your engine would drive you, so you simply end up wasting fuel in order to have a prop spinning ineffectually under your hull.

With the right skills and attitude sailing in waves can be a great deal of fun, but much of your decision making does need to depend on your crew. If people are prone to seasickness, is there much point in continuing on?

Even if you are really struggling downwind, there is much to be said for taking control of the situation.

‘There have been certain situations I have faced, going downwind in waves, where the boat is rolling around and you are surfing down waves and at a certain point you know it is going to go wrong.

‘For me, I think the best option then is to take control of the situation, give the helm a shove and accept the broach. Sure, you may be knocked down but at least you are prepared for it, and you are being knocked down the right way and it is not a sudden Chinese gybe,’ says Mackley.

Sailing in waves with an autopilot

Autopilots and waves do not always make for the happiest of bedfellows. Things have improved, however, with newer systems able to identify pitch and yaw and adjust steering accordingly.

Even if you don’t have the absolute latest tech, many of us have a system that can steer to wind instead of relying purely on compass heading. This option can be extremely useful in wavy conditions but it is important to ensure you are setting up your autopilot correctly.

‘When sailing downwind, because of potential surging down waves and increased acceleration I almost always set my autopilot to steer to true wind direction,’ says Raymarine’s Greg Wells.

‘Upwind, my autopilot steers a better course than I can. I usually have that set to apparent wind as fluctuations in boatspeed are less dramatic.’

Beyond merely using the autopilot as a labour-saving device, a key use in waves can be to free up hands for sail trim. A key feature in waves is the need to either set your sails up to be forgiving, or trim more as the boat accelerates and decelerates. ‘Last summer, one of our customers was telling us that during the Fastnet they sailed almost the whole time on autopilot sailing two up. This is useful sailing downwind in waves, when it’s easy to become over or under trimmed, which could see you rolling around.’


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