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A Boater's Guide to Passage Planning

A smart voyager identifies unique ocean features that can move you more swiftly over the bottom or set your plans adrift.
Boating Safety

Over the years, I've seen a handful of natural conditions repeat themselves in various locations around the world, and whether it's a current overfall in the Sulu Sea, a nine-knot ebb in Australia's Dundas Strait, or an avalanche of wave energy unleashed by Africa's infamous Agulhas Current, knowing what to expect helps you to prepare for similar encounters. And both taking advantage of them and avoiding their effects go hand-in-hand with sound seamanship.

First off, consider ocean currents and the sea floor. Littoral currents are wind- and wave-driven sand-transport systems that scour every coastline. Along the New South Wales coast of Australia, shallow water and a tenacious down-coast current can cause northbound sailors to take note of the relationship between the sea and the seabed. In this region, the friction between moving water and a shallow bottom diminishes the drift. The sandy bottom also weakens the current by sapping energy as tons of sediment is lifted and carried down coast. Savvy Aussie sailors take advantage of this region of diminished current and sail with "one foot on the beach." Doing so overnight is far too anxiety provoking for most cruisers headed north toward the Great Barrier Reef, and a tack offshore with a dawn return toward shallower water seems to make more sense. At least that's what I thought some years ago during a passage I made from Sydney to the reef.

At dusk, we headed offshore, beating into a head wind and a significant down-coast current. Staying clear of land during the darkness and returning on the opposite tack the next morning, I was dismayed to see the same lighthouse that we'd bid farewell to the previous evening. The name of the headland was Tacking Point, and once again Aussie humor had prevailed. That day, "one foot on the beach sailing" was a lesson learned!

And today I cope with such situations, whether in Australia, Baja, or just off the New Jersey coastline, by short-tacking in shallower water with appropriate caution devoted to good navigation and a perpetual stare at the depth sounder. Another alternative is to motorsail to weather while staying well inshore and capitalize on the lighter breezes of early morning. Best of all is the cruiser's prerogative to change plans, visit a new port, and wait for a favorable wind shift or tide.

Safety and Deep Water
A westward passage across the Indian Ocean can be much like the month of March, starting out a lamb and winding up more like an angry lion. Not only is arrival in Durban, South Africa, often punctuated with rough squally weather; the final hurdle to be crossed is the powerful Agulhas Current, a south-setting gyre that can make the Gulf Stream seem benign. Part of its bad reputation stems from the funnel-like effect caused by a confluence of the Natal Basin, Mozambique Ridge, and the continental slope of Africa.

During a passage from Mauritius to Durban, we had the good luck of being at the tail end of a small fleet of cruising boats separated by about 150 miles. A nasty gale developed, and we found ourselves safely ensconced in, ironically, the worst part of the storm. Friends farther ahead saw a little less wind and higher pressure readings, but they were caught in the grasp of the Agulhas Current, and treacherous opposing wind and sea conditions rolled and dismasted two of the boats. We hove to in mountainous swells and howling wind, but the deep ocean basin and the absence of current keep the waves from becoming steep and unstable. From that experience, I should've learned to steer clear of powerful currents when bad weather is in the picture, but it'd take another encounter, much closer to home, to drive home that golden rule.

The second lesson came with a foolish sprint from Florida to the Bahamas and a race against a fast-moving cold front that was forecast to cross southern Florida within 24 hours. We departed with the wind already veering south and trending southwest, a sure sign of the approaching front. The Gulf Steam and wind were running in the same direction, and Wind Shadow, our Ericson 41, was going north about as fast as she was going east. It was during this passage that I learned firsthand what a "pre-frontal-trough" is all about.

In essence, it's a dense band of torturous thunderstorms that are often more violent than what's found in the cold front itself. But on this particular night, the cold front around 0200 proved to be just as nasty. The only wise decision I made was an early swap of the double-reefed main and staysail for a storm trysail and storm jib. When the northerly wind shift finally slammed through and the wind-on-sea effect began to take hold, we hove to in a fierce tempest, this time not off the Cape of Good Hope but embarrassingly close to Palm Beach.

Monday-morning quarterbacking showed that the vigorous winter cold front and a midlevel trough had teamed up to turbocharge the Gulf Stream squalls. By early morning the next day, we'd ridden Benjamin Franklin's "river in the sea" to the north end of the Little Bahama Bank. We learned an important lesson about racing a cold front across the Gulf Stream: it's a shaky gamble with a big downside.

Capes and Shoals
Several round-the-world voyagers have found worse conditions rounding Cape Hatteras than they've encountered rounding Cape Horn. There's even a fleet of Volvo Ocean racers who'd echo that opinion. The region can be justifiably called a confluence of woe. It's a part of the ocean where coastal lows deepen rapidly and the heat energy of the Gulf Stream actually moves quite close to the shore. Add to this a labyrinth of shallow sand shoals projecting well out into the Atlantic, and it's easy to see why when bad weather stalks Cape Hatteras, the deck is stacked against those caught in the shuffle.

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