Bottom of the World, Top of the Crest

A 25-footer on the beam tried to end a couple's Tasman Sea crossing, but the boat and its crew prevailed.

The Tasman Sea can be a lonely place, and when the wind and currents collaborate, large and dangerous waves can cause cruisers no small amount of trepidation.

We have crossed the Tasman Sea three times in two different boats, and each time the body of water between New Zealand and Australia has demonstrated why it is among the top five notoriously difficult and dangerous seas in the world.

Our recent crossing in March 2019 aboard Buffalo Nickel was supposed to be our easiest, but we encountered the largest waves we have seen in more than 36,000 miles of cruising in the past 10 years. And it humbled us.

So here’s the story about how we were caught by a nearly vertical 25-foot wave directly on our beam, and why we never want that to happen again. This is also a story about the risk of getting complacent and overconfident, and how the ocean will almost always make you pay if she finds you in that state of mind.

Buffalo Nickel is a Steve Dashew-designed FPB boat built for ocean cruising.

The 1,100-mile route from the northern tip of New Zealand to Sydney, Australia, took us on a line virtually due west. The forecast from Whangarei to Sydney looked favorable, and our weather router gave us a hearty thumbs up: mild winds (10 to 20 knots) and following seas for the first four days, with some increase in wind to 30 knots on only part of the last day, shifting to the north and hitting us directly on our starboard beam. Beam wind and seas are normally fine with us, because Buffalo Nickel’s FPB design gives us a good ride in all directions. That, combined with our ability to maintain a speed of about 10 knots in all conditions, adds a measure of safety that we appreciate every time we venture offshore.

Sea state also looked good to us, with waves, even during the last 24 hours approaching Sydney, predicted at four to six feet, again on our starboard beam and fairly normal for us on a long passage. Our weather router told us to expect current from various directions at up to 1.5 knots.

But about halfway through our five-day passage, the barometer dropped a few points and the forecast began to change. Roughly 160 miles from Sydney, our boat speed slowed from our normal 10 knots to 6 to 8 knots, and our boat position on the chartplotter showed us crabbing severely. Buffalo Nickel was pointing north about 30 degrees off our course over ground.

Roughly 160 miles from Sydney, boat speed slowed from a normal 10 knots to 6 to 8 knots, and the boat’s position on the chartplotter showed it crabbing severely. Buffalo Nickel was pointing north about 30 degrees off our course over ground.

This was from the effect of ocean current on our boat speed and direction. At the time, we noted the current, and our reaction was annoyance, because the current was slowing our speed substantially and threatening our plan for a daylight arrival in Sydney at the end of a long voyage. This was a huge mistake on our part, because in retrospect we knew that current mixed with wind can create unpredictable and nasty waves. This is the complacency part of the story.

The situation then deteriorated further. Soon after, the orientation of the boat on the chartplotter changed to where our boat heading was about 45 degrees south of our course line. The current direction had changed and was now coming from the south. Our speed dropped to as low as 6 knots. Four knots is major ocean current, and still we did not put the pieces together. We knew the wind would build to 30 knots on the last day and that it would be from the north. Duh, wind from the north and current from the south should have told us that trouble was ahead, but we underestimated the Tasman Sea. This is the overconfidence part of the story.

 

Stay Current

Mariners use the Beaufort Wind Scale to predict wave height. It’s been around for a long time and is a mathematically accurate tool. Winds on our last day were predicted to be 30 knots. Using the scale, we should have anticipated waves of 13 to 19 feet, based on Force 7 of the scale.

We’ve been in 30-knot winds before; in fact, on our first crossing from New Zealand to Fiji we encountered winds of 40 knots and large waves, but they were not affected by current, so we rode up and over them easily. The reality is that despite a lot of time on the water, we rarely encounter significant ocean currents, largely because we just haven’t been to areas where they are common.

The Tasman Sea is different. It has a major current called the Eastern Australian Current, which flows predominantly north to south along the southeast coast of Australia. Our previous Tasman Sea crossings were north of this area, so this passage was our first encounter with this current. We saw a map that showed the current on the day after we arrived in Sydney. We did not have this information during the passage, which was another major error on our part and a function of not using all the available information at our disposal. It is worth pointing out that the direction of the currents is quite variable and that the red zones are speeds up to 4 knots. Our path took us directly through the worst zones.

Seemingly random ocean currents, the fastest of them in red, combine with wind to create potentially dangerous waves.

As with most stories about things that go really wrong, there were other factors that contributed to our meeting with a monster wave. Taken alone they would be annoying, but when put together in the right combination and in the right sequence, the result can be more than the sum of the individual parts. A moonless night, the end of a five-day passage, Val being sick and unable to take the helm, and Stan being at the helm for 12 hours all contributed to us continuing on a westerly course with waves on our beam opposed by current from the opposite direction.

[Note from Val here. Isn’t he sweet to say I was "sick?” That way you picture me off barfing someplace, which, OK, isn’t very attractive but can happen to anyone, right? The reality is that once we started on Mr. Toad’s Wild Ride in the middle of that black night, I was anxiety-ridden and incapable of standing my solitary watch. I stayed in the great room with Stan, bringing him food and drink and whatever else, in between sucking my thumb in a fetal position on the settee and avoiding looking at the white foam snaking ominously past our windows at eye level. Now back to your regularly scheduled programming.]

We could tell by the boat movement that the waves were big, but we could not see them in the dark. Even with the forward floodlights on, we did not appreciate just how bad things had become. When the sun finally began to rise, we were surprised at the sea state around us and finally started to alter our course. We headed south so the swell was behind us, then later aimed more northerly and jogged over the big waves.

One of the most confusing parts of this story is the way the Tasman Sea would suddenly settle down and have us thinking the worst was behind us, only to build again dramatically. In retrospect we realize this was due to transiting areas with less current, but at the time we did not appreciate this. As the waves settled in these areas, we turned westerly again, toward Sydney, because we were tired and wanted to get to safety as soon as possible. It was during one of these periods back on our original course that I looked to starboard and saw a large wave approaching directly on our beam.

When they’re not battling 25-foot waves, Stan and Valerie get to enjoy isolated and beautiful anchorages in the world’s most exotic places, including this spot in Palau.

For all of the reasons noted above, we continued on course as we watched the wave approach. Suddenly, with the wave about 50 yards from the boat, it combined with a wave from a slightly
different direction and the manageable 15-foot wave became a 25-foot wall of water, nearly vertical and ready to break. We did not have time to turn into this monster and it hit us directly on the right side. As Buffalo Nickel started up the wave face, she listed to the side as far as we’ve ever experienced, and at the top I just waited to see which way we would fall. Luckily for us, we proceeded over the back of the wave.

 

Learning Lessons

So, what did we learn and what do we now understand better? We knew that wind-wave height is dependent on wind speed and direction, fetch, ocean bottom depth and contour, and current. We appreciate now that when wave peaks combine, they are 100 percent additive, meaning that two 10-foot swells meeting with their peaks in sync will result in a wave 20 feet high. We understand that opposing current is more dangerous than prior experience had taught us, and current evaluation and monitoring in the future will be a bigger part of our passage planning.

Before their perilous crossing, the Creightons enjoyed some time at Bay of Islands in New Zealand.

If a future course puts us in an orientation with increased risk, we will change course earlier, especially in any condition where the wind speed is greater than 30 knots. This recent Tasman Sea crossing also caused us to go back and rethink what we now know about waves and currents and apply it to our own boat:

  • Weather reports of “significant wave height” that mariners routinely use are the mean of the highest one-third of waves.
  • We know that mixed in with these seas will be periodic waves twice as high, and it is not unusual to encounter these large seas as often as every four to 12 hours. Looking at the Beaufort Scale, that means in the same Force 7 conditions we experienced, we can expect to see waves as high as 26 to 38 feet. This means that the concept of “rogue waves” is obsolete.
  • We will never again look at 30 knots of wind as “no problem.”
  • Major currents contain lots of eddies that can change speed and direction frequently and be well outside the predicted current path.
  • Opposing current and wind make seas higher and steeper.
  • Steeper waves are more dangerous because they can break.
  • To capsize a boat, the wave must be breaking.
  • A wave will break if its wave length — peak to peak or trough to trough — is less than seven times its height. In other words, a 10-foot wave with a wave length of less than 70 feet will break.
  • It is difficult to estimate wave height or length from inside a boat.
  • The position of the boat relative to the wave determines the risk inherent in a breaking wave. Stern- or bow-to the wave face are the safest orientations; beam-to the wave face is the most dangerous.
  • Resistance to capsize goes up exponentially with boat size.
  • Research models show that many boats will capsize when breaking waves reach a height of 30 percent of boat length. At a wave height of 60 percent of boat length, any boat can capsize.

We can conclude from this that Buffalo Nickel met two of the three criteria needed to capsize: beam-to orientation and wave height greater than 30 percent of boat length. However, the wave that hit us was not breaking. We were very fortunate. We believe, since the wave face was almost vertical, the wave was very close to breaking. Our boat design improved our risk profile, as FPB boats are designed and built with all of the above considered. Working with our boat’s designer, Steve Dashew, after this episode, we concluded that we were probably heeled over to about 35 degrees. The boat’s stability curve peaks somewhere in the 75- to 95-degree range, thus we stayed upright. Even knowing this, we never want to meet a wave like this again. And we will never again get complacent or assume we are safe just because we have the best boat in the world. The sea does not care.

Follow the adventures of the Creightons and Buffalo Nickel at buffalonickelblog.com.

2 thoughts on “Bottom of the World, Top of the Crest

  1. The hypothesis that “many boats will capsize when breaking waves reach a height of 30 percent of boat length” is simply not true. A 50 foot sailboat, even with a shoal displacement, would never come close to capsizing in 15ft seas. This may be true for powerboats, but not for hulls with any decent displacement characteristics. Overall, very interesting and informative story.
    Dean

    • Hi Dean,
      We put this comment in the article to emphasize that a 15 foot breaking wave is releasing much more energy than a 15 foot seaway/swell and is therefore potentially more dangerous to the boat and crew. The comment references “research models” that may not reflect real-world experience and a better narrative might have said the boat “may capsize” rather than “will capsize”. The point is that the crew should be much more vigilant if they are in breaking seas: it’s bad enough if they are not breaking.

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