Navigation

"Scientiae Cedit Mare"
"The sea yields to knowledge"
 

Charts and Passage Planning
There are many routes one can choose to take across the Atlantic Ocean. The most direct, and arguably the fastest is the Great Circle Route. This is the shortest distance between two points on a spherical surface. This can be estimated using a Great Circle or Gnomonic Projection chart (see Figure 1).

Once the co-ordinates are taken for key points along the great circle chart route, these can be extrapolated onto a more commonly used Mercator Projection Nautical passage chart for everyday use (see Figure 2). On closer proximity to land, appropriate lower scale nautical charts (paper and digital) will be used for offshore sailing.

Along the journey ongoing chartplotting will be conducted digitally, and marked on paper charts, as well as recorded regularly, along with other relevant data (exact co-ordinates, time, wind direction, speed over water, speed over land, barometric pressure) in the log book by the captain/navigator or shift leader at regular intervals. Celestial navigation records will be kept separate but will be taken in addition to GPS and log co-ordinates and will be addressed in more retail later.


Ocean Currents

In addition to localization, a navigator must also consider the factors that will affect the vessels navigation at sea, including tidal streams and ocean currents. Tidal streams are a common factor in offshore sailing in the North Atlantic where the difference in high or low spring tides can reach up to 10 m. Ocean currents are however part of the thermohaline circulation of the worlds oceans by different density and temperature gradients. The measure if a ocean current is a mean and it runs in the same continuous direction. One of the challenges that faces those who take the Northern passage to North America is that the predominated direction of the North Atlantic ocean current is against the direction of the passage. This warm current, originating from the Caribbean is called the North Atlantic drift.

Estimates regarding the strength however vary, as the current itself is considered weak and variable, average flow of around 0.2 kn from wet to east. Direction is variable  and can be seen with more recent variable data, the month of May is shown below, from both the Irish Banks (including the Bennet currents) and the Newfoundland Banks (including the Labrador currents) in Figures 5 and 6 consecutively.

In addition to the predominate currents , this also affects the wave conditions, especially where two currents intercept. These currents are also heavily influenced by the bathymetry, which also affects ocean conditions, and predominate wave heights in the area. These are particularly noticeable in approaching underwater plateau's such as those found in the great banks of Newfoundland, the Flemish Cap and even the Irish Plateau (Figure 7).

As such in the case of Figure 7, depending on prevailing weather systems and ocean conditions, a more southerly route through the mouth of the Irish plateau may provide less wave action as the the waveform is dissipated more slowly and evenly.
Shipping Lanes
The North Atlantic Passage is a major shipping route between North America and Europe (Figure 8). Shipping can be a major source of danger at sea for the sailing vessels. Large container vessels have poor visibility in the high seas, are very fast and not very maneuverable. In contrast, sailing vessels are much slower, very maneuverable, and basically invisible. Another danger from shipping is lost cargo containers, that work effectively as sinking hazards to ocean going vessels.

Generally, the rule of thumb is to steer clear of predominate shipping lanes, taking the more northerly great circle passage should avoid most of the traffic (Figure 9) and in particular avoiding the shipping approaches most often programmed into autopilot systems (Figure 10). Unfortunately however, once in the open ocean there are no controlled traffic ways or predominant shipping lanes other then what is the most economically viable (shortest distance). So crew must all be aware of the environment and attentive to possible dangers, especially in high of foggy sea conditions.