The Blue View - Methane Bubbles

When we are at sea, there are any number of things to worry about. Storms, freak waves, partially  submerged containers, cranky whales, lightning, ships, pirates, and serious boat malfunctions top the list, and have been the cause of many a lost vessel. We've had a few close calls over the years. We've also had several friends and a number of acquaintances who have lost their boats, and in some cases their lives, from such calamities. Sometimes these things are due to an error in judgment; sometimes the daily routine lulls the crew into a false sense of security and complacency; but often, it is purely bad luck. As if the list wasn't already long enough, I just read of a new menace for mariners to worry about ... the dreaded methane bubbles. When we were parked in Puerto Lucia Marina in La Libertad, Ecuador a few years ago, we were fascinated by all the bubbles that continually percolated their way to the surface of the water. It turns out that there are methane gas and other petroleum deposits just under the earth's surface there, and the methane continually bubbled to the surface. They had built an elaborate catchment system to try to  harvest the gas, but for whatever reason, it hadn't proved viable.

While the La Libertad methane bubbles were an interesting, but innocuous, phenomenon, apparently methane bubbles in a much higher quantity could conceivably sink a vessel - even a large ship. It has long been known that large concentrations of frozen methane hydrates exist just below the sediment on the ocean floor. University researchers in both Great Britain and Australia have proposed a theory that portions of these concentrations could break free due to seismic tremors and earthquakes. As it floated towards the water's surface, the methane would change from ice to gas, forming bubbles which would then reduce the buoyancy of the water. If there was enough methane, any vessel caught in the cloud of bubbles would sink within seconds.

Proponents suggest that this might be the reason any number of vessels have disappeared without even a distress call. They show, as evidence, the presence of a sunken vessel in the center of a large methane hydrate eruption site in the North Sea.

Critics claim that such eruptions occur only rarely - maybe once every 400 years - and the odds of a ship being in that precise location at the exact time of the eruption are infinitesimally small. On the other hand, I remember reading that the early designers of offshore drilling rigs designed them to withstand a 50 foot wave, because it was estimated such huge rogue waves only occurred somewhere in the world every decade or so, and the odds of any one drilling rig getting clobbered by a wave bigger than that were minute. Now that satellite imagery can track such things, however, it seems there are actually something like 100 rogue waves that size or larger somewhere in the world's oceans at any given time. It's still quite unlikely an oil rig will get hit by such a wave, but the odds are much higher than the designers thought.

As for us, we aren't going to worry too much about the "Ocean Flatulence" theory - it's one of those things we can't do a thing about. If it is a real phenomenon, we can only hope that Neptune enjoys his tot of rum enough to keep us clear of that particular type of night wind.

Note: Despite Marcie's encouragement to the contrary, notice how I avoided incorporating any sophomoric 'fart' humor in this Blue View, like "we have enough flatulence aboard without worrying about Neptune's farts". I am much too sophisticated for that.

The Blue View - The Great Circle Route

If you were planning a long sea voyage and wanted to take the shortest, most direct route, one way to determine the course would be to take a globe and put a string between the start and end points. Assuming there weren't any landmasses or other obstacles on the route, the string would mark the shortest route.

The string would lie along the great circle joining the two points, which, as defined by Wikipedia, is “a circle on the surface of a sphere that lies in a plane passing through the sphere's center. As it represents the shortest distance between any two points on a sphere, a great circle of the earth is the preferred route taken by a ship or aircraft.”

Few sailors, however, rely on a globe and string for navigation. Instead, routes are planned and plotted using flat paper charts (or, more likely, flat chartplotter screens). A straight line drawn between the start and destination on a traditional Mercator projection chart is called the rhumb line and is not necessarily the shortest route, however. So how is the great circle route determined?

If your math skills are good, the great circle route between any two points on the globe can be calculated using spherical trigonometry. A simpler method is to use another type of chartset, called the Great Circle Sailing Charts. These use a gnomonic projection as opposed to the usual Mercator projection of the world. On a gnomonic projection, the lines of latitude are drawn as arcs. A straight line drawn between any two points on these charts lies along the great circle between the points, and is the shortest possible route. The great circle charts cannot be used for navigation, however, so the route must be transferred to the usual navigational charts.

Not that many years ago, to create a great circle route, I would plot the route on the gnomonic charts. Then I would create and measure waypoints along the great circle route a few hundred miles apart, and transfer them to the Mercator charts. If I connected the dots, I would then have a close approximation to the great circle route on our regular paper charts. The route would then have to be closely checked to make sure we weren't going to sail through a reef or island. It took a lot of time and it was quite easy to make errors, so Marcie would always check my work.

Now, of course, chartplotters do all the work for us. For example, when plotting a course on OpenCPN, a PC-based navigation program that we use, when the correct options are set, the program will display the difference in nautical miles between the rhumb line route and the great circle route and will then plot the route either way. A nice feature!

Some rules of thumb regarding great circle routes:

Since lines of longitude are great circles of the earth, the rhumb line for a route that runs north-south will also be a great circle route. The only latitude line that is also a great circle is the equator. The further an east-west route is from the equator, the more the rhumb line distance will vary from the great circle distance. For example, if sailing from Cape Town to Melbourne, the rhumb line is more than 600 nm longer than the great circle route, while the difference between the rhumb line and great circle distances for a route between Ecuador and New Guinea is only about 85 nm.

On long passages that run both east-west and north-south, the difference between the rhumb line and great circle distances is often very small. An example is the route from Cape Town to New York, which varies only about 50 nm between the rhumb line and the great circle distances.

The Blue View - St. Helena Driving Tips

The scenery on St. Helena Island is fabulous, with mountain and sea vistas everywhere. We wanted to explore as much of it as we could, so we hired a car for a few days.The total area of St. Helena is about 47 square miles. I don't know how many actual miles of road there are, but I do know we drove most of them. The driving here is somewhat different than in other places, and I thought I'd share a few driving tips I discovered.

Drive on the left.

This is a British territory, so you drive on the left here. If you aren't used to driving on the left, it's easy to forget and find yourself in the wrong lane. Even harder is remembering which lever is the turn signal and which is for the wiper blades. These are reversed in a right hand drive vehicle. You can always tell when an American is driving, because we signal our turns with the windshield wipers.

The car.

Don't expect that sparkling new car that you might rent from Avis or Hertz. Our car was a rather battered, sixteen year old Toyota. When we did our initial inspection, rather than making note of any scratches and dings, we noted the areas that weren't dented. The clutch engaged about an inch off the floor and it took about three tries to get it into reverse. The “check engine” light was on, and the ignition switch apparently gave it up some time ago. The door locks weren't a problem as no one locks their car here anyway. To start the car, the ignition was switched on with a toggle switch, then a pushbutton switch was pressed to engage the starter. The modified system worked just fine, and eliminated the need for such superfluous things as keys. Despite its age and condition, it ran just fine and we had no problems with it.

The emergency brake.

The most important item on the car – make sure it works. I used it not only for keeping the car where I left it when it was parked on a steep incline, but as an aid when starting up after stopping on a hill.

The horn.

The horn is the second most important item on the car. It is used frequently when approaching one of the hundreds of blind, hairpin curves on the narrow roadways to warn drivers coming from the other direction.

Speed.

Distances are in miles and speeds are in miles-per-hour – the only place outside the U.S. we've been that doesn't use metric units. The maximum speed limit on the island is 30 MPH. I thought of it as more of a goal than a limit – in four days of driving, I don't think I found a stretch of road I could go that fast.

Right-of-way.

When two cars approach each other, the car going uphill has the right-of-way. If the road is too narrow for the cars to pass, the car going downhill has to back up until the road is wide enough. We had to back up a good quarter of a mile when we encountered a car as we were leaving the High Knoll Fort after our visit there.

Standard Transmission.

As is the case in most places outside the U.S., the rental cars are all standard transmission. On St. Helena, it is only necessary to have a two speed transmission, however. I never had occasion to drive fast enough to use 3rd, 4th or 5th gears.

Waving.

Every driver and pedestrian we encountered waved to us. We got into the habit of waving back, although it was difficult at times when I was busy downshifting from 2nd to 1st while blowing the horn and shutting off the wipers after signaling a turn.

Obstacles on the roadway.

In Tasmania, we were constantly on the lookout for marsupials in the roadway – wallabies, wombats, Tasmania devils, etc. In South Africa, we were watchful for boks – springboks, rheboks, gemsbok and kudus. Here it was the occasional goat leaping out or the odd cow lying in the road. And the island is a laid back, slow paced kind of place. It is not unusual for someone to stop their car in the road and have a nice chat with a friend walking along. We encountered a car parked in the middle of the road with four or five people standing next to it. I stopped and asked whether they were having problems. “Nope – just having a yarn” was the reply. We soon learned that no one had a problem when we stopped in the road to take a photo or admire a view.

The roads.

While the roads are narrow and steep with switchbacks and blind curves everywhere, they are in quite good shape. Most are paved and have very few pot holes, and with few exceptions, the gravel roads we traveled were smooth and well graded.

Fuel.

Fueling up requires some planning. There are only four gas stations on the island, and their hours are limited. No fuel is available on Sundays, and they are all cash only.

Maps.

The local tourist road maps are confusing. They don't show all the roads, aren't quite to scale, and since many roads don't have signs, we were often not quite sure as to where we were or which fork to take. I suppose some people would refer to this as being lost, but I think that is far too strong a term. Anyway, Marcie had had the foresight to download the St. Helena maps for our iPad app “Maps with Me”, which was amazingly accurate and detailed. After our first day of driving using the local paper road map, we relied on the electronic map and had no problems.

Overall, we had a great time driving the island. Other than a few stressful moments getting used to the driving etiquette here, we had no problems. The car ran fine and the other drivers were forgiving of my mistakes. And by Day 4, not only was I getting into the car on the correct side, I was better than 50-50 when signaling a turn.