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Old 02-01-2002
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Michael Carr is on a distinguished road
Routing Principles Redefined


Prudent navigators know the value of minimizing the time spent bucking the winds, waves, and currents.
Do not, I repeat, do not try to transit west to east in the Caribbean. Veteran sailors know that the easterly and southeasterly tradewinds in this region, and the waves and swells that they relentlessly manufacture, make such a transit extremely painful at the very least.

So guess what I am doing at this very moment—January 19, 2002 at 3:38:59 p.m.? I am heading east from Trinidad to Tobago aboard a 360-foot RORO (roll-on roll-off vehicle and passenger ferry). We’re travelling in the wrong direction and I am paying for it as we pitch into large trade-wind swells and strong easterly winds. Not only am I doing this right now, but this is the second time in two days I’ve made this trip and I am going to do it five more times before I stop. (Some people have accused me of not catching on too quickly, and now I'm beginning to see their reasoning.)

Not only is this transit painful when heading east, but it is also painful heading back west to Trinidad to start over again. When we run downwind and downswell this massive vessel is prone to rolling, and those long, slow rolls give you time to appreciate fully the sensation as well as prompting you to wonder how many more rolls it will take before your stomach rebels.

I should count my good fortune though because I am on a vessel that can make 18 knots, so the 96-mile expanse between these islands is quickly eaten up. Also, the last hour both ways takes place in the lee of the land where the wind and swells are markedly diminished. But the open-ocean section between the two islands is tough on the mind and body. All of this causes me to wonder if I am getting soft as a seaman.


Winds blowing across hundreds of miles of open ocean can and do produce powerful swells that often amount to a considerable challenge for mariners.
On a more intellectual plane, what this experience tells me is something I have known for years, that those formulas and descriptions in Bowditch regarding wave formation, propagation, and dispersion are absolutely correct. Twenty knots of wind blowing across hundreds and thousands of miles of open ocean will produce powerful and large swells. And when wind and swells are funneled through and around island channels, their energy is compressed, the wind speed increases, and the swell height goes up, and up, and up. I only have to look out the ports here to know this is true!

A long-accepted routing principle states the obvious regarding this kind of situation: the shortest time route between a point of departure and arrival is not necessarily a straight line. Often the appropriate route is a large arc that minimizes one's exposure to adverse wind and waves. If I were on a sailboat at this moment, and not this high-powered RORO, I might be tacking around and heading for the Trinidad airport. So as I sit here typing away, bracing myself against each pitch and roll, I am reminded of the list of Steps to Successful Routing (see sidebar below) that I contrived a few years ago. The idea behind the list was to help me keep in mind what I needed to know in order to take the most comprehensive and prudent approach to planning a route. I've used it constantly since, and still do, except for trips like this one where someone else bears the ultimate responsibility.


Though seagoing ships have the power to mitigate many of the ocean's adverse elements, their navigators know and apply the proper routing principles when necessary.

At the moment, on board this RORO, there is no routing going on to speak of. We (I am using the royal we, as I am a "passenger" on these transits, here to train the crew on the use of survival gear such as liferafts, immersion suits, and EPIRBs) are following the same trackline both east and west bound. This track keeps the RORO a good 12 miles from land so that the on-board sewage tanks can be pumped. (This is in accordance with marine pollution laws, MARPOL.) And since this is a relatively high-speed vessel that can punch through moderate seas, the duration of encounter with head seas is no more than four hours (though for many passengers like myself those can be a long, long four hours).

In just over two days (yes, I am counting the hours!), I will depart the Caribbean and fly back to the US. (Nothing goes to windward like a 747!) I hope to get home just in time for Sail Expo in Atlantic City, where I'm scheduled to give a presentation on "Winds and Waves" for Cruising World magazine. And you can be assured that I will find an opportunity to emphasize to my audience the importance of not attempting to sail upwind in the tradewinds!

Carr's Essential Routing Steps

1. Determine your vessel's performance, capabilities, and limitations and, if possible, enter this data into a routing software program. Or at the least have printed data showing the vessel’s capabilities in a range of wind and sea conditions.

2. Learn to read and use 500-mb charts, surface charts, sea-state charts, wave-period charts, and satellite imagery, and then combine that information for your route with your knowledge of the vessel’s and crews’ capabilities.

3. Calculate and evaluate present and future weather conditions using all available voice, text, chart, and satellite imagery data.

4. Calculate the shortest physical distance, which is often a great circle (GC), between the point of departure and your destination.

5. Calculate a minimum speed necessary to complete this route in the time available. Institute speed management, i.e. if you’ll be traveling full speed ahead 100 percent of the time, you will often sail out of desired wind and sea conditions. The objective is to stay within desired weather by increasing or decreasing speed, while always keeping the vessel above a minimum acceptable speed.

6. Evaluate alternative routes that show the advantage, or minimize the disadvantage of wind, seas, topography, currents, ice, and vessel motion limits.

7. Adjust or tweak your chosen route in consideration of navigational restrictions, i.e. waypoints.

8. Stay on shortest physical distance (great circle GC) when that is the fastest route, but move off the GC when a longer physical route will actually produce a faster passage time.

9. Continually evaluate and re-evaluation routes other than GC, which may better satisfy your objective of reaching the destination in the shortest amount of time.

10. Evaluate and adjust course at least every three hours, but at no time sail for more than six hours without evaluating conditions and performance.

11. Always "sail" ahead of your vessel mentally by 24 hours to anticipate problems.





Suggested Reading:

Route Planning 101 by Michael Carr

At Odds with the Weather Gods by John Kretschmer

Caribbean Routing Advice by SailNet

 

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