How To Sail In Big Waves
Yachting Monthly|February 2020
Toby Heppell finds out about the best rough weather tactics to keep you Sailing for speed, comfort, safety and enjoyment

Sailing in waves can be a jarring, juddering experience, making for a long and uncomfortable passage, a thrilling surfing ride to your destination or, at worst, a dangerous, boat-rolling hazard.

Understanding how to set up your boat for differing wave conditions, 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.

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.’

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 ata 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

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 that 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 anything, 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. 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 ata 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. 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 AROUND

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