You know when you’ve been hit by a rogue wave. The energy within it is of a different order of magnitude from an inconvenient, but ultimately harmless, wave crest that topples into the cockpit.

The first such wave I encountered was more than 20 years ago in the Southern Ocean while being pummelled by a secondary low that produced gusts above 60 knots. Those on deck were swept to the limit of their harnesses. Water streamed through the closed washboards as though blasted from a fire hose. Fortunately we sustained no serious damage and were able to continue to Cape Horn.

The second rogue wave was much closer to home – 130 miles west-north-west of La Coruña in north-west Spain – and immediately put paid to any plans other than saving the boat. We (myself and my partner, Kass) were sailing two-handed in Zest, a one-off 36ft Rob Humphreys design, having left Cowes on 13 October last year. We were bound towards Lanzarote, with the ultimate aim of spending the winter in the Caribbean.

Although in long-term voyaging mode, with Dacron sails and a heavy cruising inventory, we had effortlessly made more than 600 miles in four days. In the run-up to the incident, the Pacific Windpilot had been steering on a wind angle of around 165°, with a small amount of headsail unfurled. This gave us a speed of 6.5-7 knots, enough for accurate steering, but not for Zest to surf quickly down the face of the waves.

It felt safe and relaxed compared with the big winds we’d experienced on downwind legs on some of the races we’d completed when we’d been pushing hard.

The waves had been driven for several days by an east-north-easterly airflow that slowly built to a mean speed of more than 40 knots at times. We estimated significant wave height of around 3.5m, but the crests were well spaced out and not breaking, so each one would pass quietly underneath Zest.

Had a breaking wave caught us beam on, in theory it might have been large enough to capsize a boat of Zest’s beam. However, by presenting the stern to the waves and keeping the speed low enough to avoid a risk of pitchpoling, we felt safe and secure, reassured that others had survived far more challenging conditions in a similar manner.

At the time of the incident we were both below deck, sitting on the lee settee and talking about the forecast, waiting for dinner to finish cooking. The wind was forecast to moderate to only 10-15 knots at dawn, before picking up again after a 24-hour breather. All we had to do was route safely to the west of a couple of small, but intense, low pressure systems off the Portuguese coast to hook into a clear run to Lanzarote.

Massive thud

However, our conversation was interrupted by the disconcerting roar of what sounded like a huge breaking wave coming roughly from amidships on the port side. It was totally unlike the rest of the wavetrain and hit Zest with a massive thud. A big lurch to leeward was instantly followed by the sickening noise of timber being torn apart. Then the lights went out.

In the immediate aftermath of structural failure the extent of the damage is not always obvious. It certainly flashed through both our minds that we might need to rush for the liferaft, grabbing the EPIRB on the way. But the saloon wasn’t immediately engulfed with water – and it didn’t appear to be cascading in from overhead.

I asked Kass to pass me a torch. On examining the area where the port chainplate had been only moments earlier, I reported: “There’s a f***ing big hole in the boat.” She told me not to be melodramatic.

While I continued to examine Zest’s structure, Kass looked out on deck to check the situation there. The keel-stepped mast had broken a couple of metres above the deck and was hanging apparently harmlessly over the starboard side.

Meanwhile, Zest had rotated downwind of the rig, which was now acting as a sea anchor. This both stabilised the boat and also helped keep the hole in the port side deck clear of solid water.

As I examined the structure from the inside I thought what an enormous help it was that Zest is of a high-tech timber construction (strip cedar and epoxy) and therefore doesn’t need the multitude of headlining panels and coverings that provide the cosmetic finish to most boat interiors. While a portion of the main bulkhead had carried away with the chainplate, taking with it a 6ft x 2ft section of the port side deck, there was only minor damage to the beam shelf and none to the hull.

Initial recovery

Given the limit of the damage and the fact that we weren’t taking significant amounts of water over the deck, we were not in any immediate danger and therefore had time to get organised. Clearing the rig away was not unduly difficult, though with the mast lying across the starboard side of the boat, threatening to drag anyone there over the side, plus a gaping hole on the port side deck, it required careful planning and a methodical attitude.

We knocked the pins out of all shrouds that were not under tension before using a cordless angle grinder to cut the only one in tension – a 10mm Dyform cap shroud. Similarly, sharp knives put paid to the internal halyards, allowing the mast to slip into the sea.

 

Given the stabilising effect of the rig in the water, we initially left the forestay attached, with the rig hanging off the bow, acting as a makeshift sea anchor. At this stage there was rope everywhere and it was a pitch back night with no moon. We were therefore happy to wait until dawn before finishing tidying, starting the engine only once we were quite sure there was no risk of a rope round the prop. We could also recover from the initial shock.

We already knew there was no chance of making port before the next gale, so to stop green water cascading below decks we stuffed the hole in the deck with bagged spinnakers (we had five on board), pillows, fenders and anything else that came to hand.

We emailed shore contacts and Falmouth Coastguard to appraise them of the situation, while making it clear that we were not in need of assistance. At the same time we set the Iridium GO’s automatic position reporting facility to provide hourly updates, so that our progress could be monitored.

Heading for safety

At first we set off in a gentle breeze, but a large leftover swell, heading towards La Coruña, hand-steering as the NMEA 2000 data bus had been disabled and the pilot didn’t work. By nightfall the wind was starting to increase, so we bore away, heading for a destination further south.

It was easy to identify the new marina at Muros as the best option – good all-round shelter and a safe approach. Had we encountered engine problems when closing the shore, we would have blown offshore into safe water.

 

By the second afternoon we were in winds gusting well over 40 knots. Fortunately, by now we had gained some shelter from the land near Finisterre and were accompanied by hundreds of dolphins, with dozens of them simultaneously jumping out of the wave crests.

On the downside, we were now taking quite a bit of green water over the deck, which resulted in enough seeping below that we needed to pump for around 20 minutes an hour. This rate roughly doubled once we turned into the ria and had 45-knot gusts on the nose for the last five miles. We finally arrived safely at Marina Muros, conveniently a couple of hours before dusk, some 45 hours after the incident.

We were carrying enough fuel to motor for 350-400 miles in flat water at a gentle cruising speed of around five knots, although that distance reduces considerably when powering against head seas. We still had enough fuel left for ten hours’ motoring when we reached Muros, but clearly had we been significantly further offshore it wouldn’t have been possible to motor to port.

Given the strong to gale force easterlies forecast to stay for several days, the Galician coast would most likely have been out of reach under jury rig. However, we had enough spares and tools to make a watertight repair to the deck, if necessary using plywood from the cabin soleboards.

 

As for a jury rig, with the stump of the mast left it would have been a relatively simple operation to lash the spinnaker pole against it, with the head supported by Dyneema stays, to create a spar around 5m off the deck.

We had enough water and food on board for a further fortnight at sea, so even at an average of only three knots we could have reached Lanzarote, or a closer harbour in Portugal, if necessary using the engine once within comfortable motoring range of port.

How high was the rogue wave?

We can only speculate on the size of the wave that hit Zest. All we can say for certain is that it was clearly a one-off breaking wave that was very significantly larger and of a very different character from the surrounding seas.

Nevertheless, the science of wave predication can help to ascertain a possible maximum limit on how large it might have been. Along with many other sailors, my long-standing belief had been that the maximum wave size that you had any chance of experiencing was twice the significant wave height – ie double the average height of the largest 30 per cent of waves. In our case that would have been around 7m.

As recently as the mid-1990s the scientific community was dubious of the very existence of rogue waves, even though there was plenty of anecdotal evidence. Everything changed on New Year’s Day 1995, when a colossal 25.6m wave was measured by a laser range finder on Draupner oil platform in the North Sea.

This was a pivotal event for a number of reasons. Firstly, the platform had been designed to withstand a 1 in 10,000-year freak wave, calculated as having a maximum height of only 20m. More importantly, scientists at last had a concrete and verifiable measurement on which to base new studies.

 

Kass worked at the European Centre of Medium Range Weather Forecasting (ECMWF) for a period, so on our return we went there to talk to Peter Janssen, an acknowledged world expert on rogue waves.

He checked the archived forecast of significant wave height at our location – 4m, so a little higher than our estimate. He then went on to explain that traditionally the definition of theoretical maximum wave height as twice the significant wave height is for a single location over a 20-minute period. This apparently arbitrary figure was chosen in the middle part of the 20th Century as being the longest period a watch keeper could effectively visually estimate wave height.

Janssen went on to explain that, if a larger geographic area is considered – for example a 10km x 10km square – maximum wave height might increase by a factor of the square root of 2 (ie 1.42 times larger). And if a longer time period is considered, by a factor of the square root of 3 (ie 1.73). So, instead of the 7m maximum theoretical wave height we expected, that would increase it to almost 14m, based on the ECMWF forecast. An area around 150 miles to our west had even higher waves, with significant height of 5.5m, giving a theoretical maximum of 19m.

Once you start thinking in those terms it becomes easier to understand how a yacht with enormous stability, such as an IMOCA 60, could be capsized in that region – as happened to Alex Thomson’s Hugo Boss two weeks after our incident.

Could it be that some of the conclusions drawn from other people’s survival of severe weather are to some extent based on a false premise? In some cases might the outcome be down to whether or not you have the misfortune to be hit by a giant wave rather than the heavy weather strategies you employ?

What we might have done differently

Given that we were heading south well after the end of the ideal season, engaging a professional weather router would have had many benefits. A knowledgeable person ashore who is able to gather data with ease – and has the time and skills to make an in-depth analysis – can bring benefits out of proportion to the relatively modest cost.

In addition, I arguably lacked my normal caution in situations where the isobars between high and low pressure systems are squeezed together. The problem here is that only a small change in the position or pressure of the centre of the low can make a very significant difference to wind speeds. Compounding that, in an effort to minimise file sizes, when we downloaded weather GRIBs we didn’t include wave data.

 

On a positive note, Zest is equipped to meet the safety requirements of World Sailing (formerly ISAF) Category 1 (transoceanic) races. It was reassuring to know that we both had recent sea survival training, along with first-rate emergency equipment, plus a comprehensive set of tools and spares.

What we learned from the event and from subsequent research reinforces the importance of secure stowage of kit both above and below decks. For serious offshore use I’m now also more sceptical of monohulls with low bridgedecks.

Even if washboards are stowed ready for use, it’s all too easy to be complacent. The same applies to multihulls with patio doors and no way to stop water in the cockpit flooding into the hulls.

Equally, it reinforces the dangers associated with entering a port with a shallow bar, such as many on the Atlantic coast of the Iberian peninsula, in an onshore swell. It only needs a big wave to appear at a critical moment to flip what initially appeared to be a manageable situation into a life-threatening scenario.

Rupert Holmes is a freelance yachting journalist with more than 70,000 miles’ experience in a wide variety of craft, including cruising and racing yachts, and significant short-handed sailing

 

Zest is a 36ft custom design by Rob Humphreys in which Rupert Holmes and Kass Schmitt have sailed short-handed more than 13,000 miles since 2013, including two trips to the Azores, the Royal Western YC’s Round Britain and Ireland Race, and the Rolex Fastnet Race.

She is now back in Cowes, where repairs are underway in readiness for Allspars to install a new rig. Zest’s next transatlantic voyage is scheduled to be the 2017 OSTAR, in which Kass is entered.