Just as there are different types or divisions of navigation ( DR, piloting, electronic, and celestial), there are also different phases of navigation. Each phase will require a certain mixture of the various types of navigation. The prudent mariner will use a number of combinations of these navigation types, as the opportunity presents itself, to get the most accurate position. The primary phases of navigation are Inland Waterway, Harbor, Harbor Approach, Coastal, and Ocean. Here's an overview of these phases, beginning with perhaps the most simple, the Harbor Phase:
Inner Harbor In most harbors, mariners are primarily navigating visually, while using devices like radar and the depth sounder to keep themselves clear of other vessels and off the rocks as they approach or depart their mooring or dock on the way to the mouth of the harbor. Not all charts provide the detail needed for mariners to safely navigate here and some local knowledge is a definite plus when operating within an inner harbor.
If you have been sailing out of your homeport for some time, you will have the local knowledge you need. However, if you are in a strange harbor, you would do well to read up on it from the Coastal Pilot and use your radio to get some local information and instructions from the harbormaster if there is one. If you are departing this harbor and have a GPS plotter or computerized charting program on board, you can save your track as you exit and follow that back in upon your return.
Harbor Approach This phase of navigation usually takes the sailor within a narrow channel or entry when approaching from seaward via various aids to navigation to the harbor entrance defines this phase. Here you will primarily be using your pilotage and DR backed up with electronics (radar, GPS and plotter/computerized electronic charting programs) to get to the entrance buoy. From here you will transition to one of the other phases. Often you will be transitioning from the coastal phase directly into this one or vice versa. Inland Waterway
This phase requires piloting in narrow channels, canals, rivers and estuaries. This usually occurs after you depart a harbor or just before you make your approach to the harbor. During this phase you also will primarily be using your piloting navigation skills and DR backed up with electronics (radar, GPS and plotter/computerized electronic charting programs) to safely navigate these narrow passages and to stay within the defined channel. Several computerized navigation and electronic charting programs have ICW routes available which have been deconflicted for shoaling and other hazards known to the locals. They are kept updated by the developers on a yearly basis. If you are using the ICW, I highly recommend that you get and use these routes.
Coastal Cruising This area is defined as navigation within 50 miles of the coast or inshore of the 200-meter depth contour. Here you are offshore, but not yet in the open ocean. This area is where you will be using every navigation resource available with the possible exception of celestial.Open Ocean
Anytime you are navigating outside the coastal area in the open seas. For example, across a Gulf or across the ocean. Here is where you will be well away from shore and your navigation will take on a rhythm of its own for days and sometimes weeks on end. DR, celestial, and GPS will be your primary means of navigation. Radar will be used primarily for collision avoidance. The depth sounder will only occasionally be used as you cross a seamount or continental shelf. The tedium of celestial calculations can be eased by the use of sight-reduction calculators and computerized celestial navigation programs.
Weather will also play a significant part in determining what aids to navigation you use in each phase as conditions can change rapidly. Obviously radar will be invaluable in heavy fog and a GPS plotter or computerized electronic charting program will be useful at all times of day or night and in all weather conditions. It is well to remember that the transition time from one phase of navigation to another can be very short. Most of the time they will blend into one another without any obvious departure point. You should also be ready at all times to use the type of navigation that will yield the most accurate position regardless of where you are in a particular phase.