Identifying lights during a Baltic Storm
|From Ocean Navigator #63 |
I was a temporary crewmember aboard the ketch Darwin Sound, an Ocean 71, built in Poole, England. On an earlier voyage aboard this vessel, I completed a wonderful transit of the Atlantic from St. Augustine to Lisbon. Alan (the owner of Darwin Sound), his wife, and two young daughters have made exploration and dissemination of nature their hobby and vocation. Their desire to teach is infectious and has brought back many guests year after year. With Greg, a crewmember we now had a complement of four adults. Under the leadership of Alan, my responsibilities had gradually grown and would continue, especially tonight, thanks to the Baltic.
The Baltic Sea, remarkably only about 7,500 years old, could more correctly be called the Baltic "pond." It is not very deep. From the Gulf of Danzig in the south the Baltic stretches northward about 170 miles, where it subdivides into the northerly Gulf of Bothnia (a further 360 miles) and the easterly Gulf of Finland (about 240 miles).
Narrow and shallow channels, many less than 24 feet deep, connect the Baltic sea with the Kattegat and, thus, with the North Sea. This is the only way any salt water is able to enter the Baltic and keep it cleansed. As a result of this, and because of a greater gain of fresh river water than that lost to evaporation, salinity is low, leaving a permanent top brackish layer. (As if to verify these facts, the watermaker aboard Darwin Sound took about 15 seconds to verify Baltic sea water as almost fresh and rapidly produced water for us.)
Why the emphasis on this shallow freshwater pond covering about 8,000 square miles? Because it does not take long to transform this pond into a writhing monster of short, steep waves that would leave a seasoned skipper ill, and show me a thing or two I will never forget.
Strong northeasterly winds had slowed our passage to St. Petersburg where we were to meet a charter party of eight. We had spent the night at Lyceby on the southeastern coast of Sweden but now were making a run for Helsinki in Finland. We planned to sail to leeward of the island of Oland, for some added protection, then skirt the north end of Gotland for a straight shot at Helsinki.
We set off early in the morning and motorsailed. On this particular day, we would never see depths greater than 120 feet.
The passage on the inside of Oland, known as the Kalmarsund, was flat and the miles rolled by. It is a navigable channel about 85 miles long strewn with shoals and islets but well supported by navigational aids. "Active navigation" is the key word here. The weather called for NE gales in the north Baltic but where we were the wind was west, on our beam,urging us onward. Once we had passed Kalmar, about half way up Oland, we did notice a distinct swell. This swell underneath the local wind waves wasn't large, at first, but was consistent. The swell grew larger, and, by the time we reached the north end of Oland, it was obvious that Helsinki, dead to windward, was out of the question. The NE gale predicted for the north Baltic did not seem such a wild prediction after all. The northerly swell was now running a good 10 feet but was still manageable. The wind had increased from about 10 knots on our port beam to 20 knots pretty much on the nose. A decision was reached. We would head for Grankullaviken, a small anchorage on the north end of Oland, and wait a few hours for the next English VHF weather update from Stockholm radio. If it was still unfavorable, this is where we would stay the night. Otherwise, we would continue to Helsinki.
Grankullaviken lay about 10 nm away, pretty much into the teeth of the wind. Our charts showed two areas of shallower water, the Byrumsgrund and the Enerumsgrund, both marked by cardinal buoys, which we would leave to starboard. Not too much trouble there. Thereafter, it looked like pretty safe water until we sighted a red buoy which marked the turn to the harbor. The entrance lay about a half mile from the turn. Getting into the anchorage would be another story, however. The channel is very narrow and doesn't allow much room for error. It was only three feet deeper than our keel, but to me it did not look a real problem. Remember, the night was still young.
With about three miles to go, the wind was only 25 knots, but the shallow sea was beginning to show its ugly side. Those swells had started transforming to an early version of the short, steep waves we would see a few hours later.
Suddenly, my jaw dropped open in disbelief. I had been peering foreword starting to look for the red buoy. Ahead, I estimated about a quarter of a mile the sea had suddenly broadly risen and broken in a massive wall of white water. It seemed to hang there an eternity then slowly disappear. We had been heading right at it. "Alan, did you see that?" I asked. He must have caught the slight tremble and disbelief in my voice. With his experience, not much phased him. Yet we hurriedly went below to examine the charts. We were pretty sure of our position, using DR, visual bearings, and GPS to navigate.
From the chart, it was not at all obvious what had caused the breaking sea. We had easily avoided the earlier shallows. There were no reefs or obstructions in the area. There were however two areas of somewhat shallower water which may have caused the huge breaker. One area, the Skansgrund, varied in depth between 12 and 30 feet and lay beyond the point at which we would turn for the anchorage. The other, about 60 feet deep, lay between us and the turning point. We changed course to give the nearer area a wide berth.
We continued to beat into the waves but, by now, had an escape route planned that would take us away from all the shallows. Finally, we got to the point where we would head into the anchorage. I went below to check the chart. I felt the boat turn, but our bow was now pointed away from the anchorage! I knew Alan well enough to know this was not some new age way of making port. We were heading full bore away from our safe haven. "Why?" I asked. "Take a look," he replied. I was handed the binoculars and stared long and hard at the entrance. There was no way we could get in there. It was difficult, at best, to discern the buoys marking the entrance. White water boiled in the channel this side of the entrance. Seas were breaking everywhere. Had I seen a few witches stirring a big black cauldron on the pier, I would not have been surprised!
I own a 36-foot sloop, and I realized I had never been in a situation where I had been unable to enter an anchorage due to adverse weather. We spoke about the dangers of undertaking such a venture -- how the channel may well be 10 feet deep at one moment, but only five feet the next moment; how a swell may suddenly break and deposit one outside the channel or cause loss of control. I think relatively new skippers like myself are continually fooled by the power of the sea. As wonderful as it to get into an anchorage, sometimes it is safer to be seasick than shipwrecked. I had read and known it intellectually, but it seems one has to be there once to really understand the emotional let down, yet also the wisdom of heading back out.
By now, the sea was showing its full fury. The wind had settled in at about 30 knots, gusting to 35. Short, steep waves turned the cabin below into a battle scene. Although we had stowed all loose objects, books and charts went flying. Navigational triangles ended up on the floor or disappeared completely. It's almost as if all of one's essential tools wait patiently for a storm then assume an anarchic persona and start roaming the boat -- just when one really needs them.
It was time for plan B. Alan had picked another anchorage whose entrance lay about 30 nautical miles to the northwest, on mainland Sweden. The navigation problem was clear. Although the town was at the head of a seven-mile channel in good deep water, a short dog-leg turn to the left had to be made about halfway into the channel. To seaward of this dog-leg, the channel was about 500 feet wide and less well defined, yet bound by reefs on either side. Two sector lights would help guide us into the channel and two cardinal marks quite far out, on our starboard hand, would provide visual position data as we sailed towards the dog-leg. A green stick that marked the beginning of the dog-leg would be kept to starboard. After this left turn, a red stick would signal the end of the dog-leg, and we would again turn right to the much better defined second part of the channel, which we should be able to see more readily on radar. We dared not miss that green stick as beyond it lay a mass of reefs. Remember, this is Europe where they don't seem to like the "red right returning" adage but use the "red wrong returning" instead. When I use the word "stick" in describing the aid, I'm not kidding. We are spoiled by our navigational aids here in the U.S. The first time Alan pointed out a navigation aid to me, I thought it was a reed sticking out of the water. No, indeed, it was a bona-fide aid.
Alan asked me to lay a course to lead us up to the outside of the channel. We would first have to motorsail around a reef and islets about five nautical miles away but this did not pose a problem. We keenly searched the horizon for lights we knew to be there. A light far to starboard, faint at first, did not match anything on the chart. Fixed red? Pretty soon it was picked up on radar as it approached us. It was a freighter. We changed course, aiming for its stern. It crossed no more than 100 yards ahead of us. Thanks to the wind, the ship passed us in total silence. I did not see a living soul, but I could almost feel the ship itself looking at us. Soon it was gone.
After what seemed an eternity, Alan and Greg started seeing lights. They identified two white lights. One four-second and one 10-second flashing. Yes -- it made perfect sense. Here they were on the chart: two sector lights -- red to port and green to starboard. This put us in the white sector and gave us increased confidence of our position. The sea was growing rougher. "What about the third light?," Alan shouted. What was he talking about? I was summoned to the deck. I harnessed myself next to Alan and was told to explain what he was seeing. I searched the horizon and it was pitch black with howling winds, and flying foam. It did not look like the orderly chart at all. One can get pretty snug and confident down in the bowels of the nav station. The DR track looks so good, going exactly where one is supposed to go. But one has to get out and make sure reality and the chart agree. As Alan later pointed out to me, it's a common error. Then I saw them: Two white lights showing 4- and 10-second characteristics, but another light also showing 4-second flashes between the two of them. It did not make sense.
Back below I went. Alan's wife and I went over the chart. Yes, there were the two lights. But the third light? There was one other light but this was way behind the other lights and not relevant. One does silly things in the quest for experience! Closer scrutiny would have revealed it to be a very narrow 4-second sector light. Seeing that everything else seemed to make perfect sense, we put this third light out of our minds. We were safe in the white sector.
Finally, we reached the channel. Soon we caught sight of the cardinal marks to starboard. Now what? We could stay within the white sector but had to find the green stick to start our turn. Alan was getting excited. I poked my head up and looked around. I saw the reason. White water was breaking on either side of us on reefs we knew to be there. He did not like this one bit. We had to find that stick. According to the chart, it ought to be about 200 feet or so starboard. Greg stood with a spotlight and peered into the turmoil of spray and wind. I went up on deck. Only later did I learn that Alan was about to turn the boat around and leave. At that moment however, the green stick appeared. I saw it first. Silently, it slid past our starboard side. Greg, still peering into the distance, had, at that very instant, leaned back slightly, or else the stick would have hit him on the head. "There it is," I yelled. There was no time to lose. We made a turn to port, and the seas were immediately calmer. Down below I went to check the next mark. The sector light was expected to change to red, and it did. But so did our third unknown one. It just did not fit, but everything else did, and the third light was again ignored. Pretty soon our next buoy appeared where it should have. Then we picked up the shore in the spotlight.
We were in. After another 45 minutes we dropped anchor in 15 feet of water and 30 knots of wind. Alan came below exhausted, took one look at the chart, stabbed his finger at the light we had seen and had ignored and said "There it is." And there it was! The light was so much further back it seemed to be irrelevant. Also, its white sector was extremely thin, a fact that I had simply missed. Depth perception at night is poor, especially if one is looking at a pinpoint of light. When I saw those three lights out there in the howling wind and raging seas, I could have sworn they were standing tall alongside one another like three soldiers in a row. Well, they were standing tall all right, but the middle light was standing tall, way back, exactly as shown on the chart. I won't make that mistake again.
What had caused that big breaking wave off Grankullaviken? Now, of course, it all makes sense. The key is wave height. Most weather services report significant wave height (SWH) in their forecasts. This represents the average highest one third of all the waves in a given period. From the deck of a boat, however, one observes an average wave height that is approximately 0.6 times the SWH. One thus needs to multiply what one sees. In our case, 10 feet by 1.3, giving us a SWH of 16 feet. Statistically, one in every 1,175 waves will be 1.9 x the SWH, or about 30 feet. How often will this happen? If we assume a wave period of eight seconds, then it is approximately every two and a half hours. A 30-foot wave will break in 40 feet of water. It will also increase in size by approximately half its height. So, we have a potential for a breaking wave of 45 feet if it finds a bottom less than 40 feet. Putting it all together, I can now say that I probably misjudged the distance. In all probability it was a breaking wave -- a big one mind you -- on the Skansgrund, about five miles away. A general rule I would draw from that experience is that one should stay in water at least four times deeper than the average wave height seen. Remember however, one is playing the odds. One in 300,000 waves will be 2.5 x SWH (this would occur statistically once every 27 days) and would be a whopping 40 feet and would break at 60 feet.
Even though Alan has been sailing for many years, he later admitted that he had never seen such seas. We heard from Finnish officials that this is not unusual for the Baltic. Smiling, their heads nodding knowingly, their hands gesturing the roller coaster motion we had experienced, they invoked the lack of salinity and shallowness for the violent seas. There is some evidence to support their claim. The transition zone between the brackish surface water and the deeper salt water (in the Baltic between 60 and 90 feet) may act as a physical bottom for a wave, thus making the depth even shallower. If a wave touches bottom, it slows and increases in height and is transformed into a steep wave likely to break.
In retrospect, it was a tough landfall that would have been more satisfying from my point of view as navigator had I been able to clearly understand and explain to all exactly what it was we saw and to predict the expected buoys and lights. Lastly, when making a difficult landfall, it is helpful to recall Sir Ernest Shackleton who, having just survived the feared Drake Passage in a 22-foot open boat, waited 48 hours before considering landing. Not seeking port should always be an option.
Michael De Haan owns a C&C 36 and lives in Seattle