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Sailing in reef-strewn waters is very dangerous. The only safe way to operate in tight reef waters is to use eyeball navigation. To do this you need to get at least six feet above deck level to view the patterns in the water.
'Rule of Twelfths': a simple method for estimating intermediate tidal heights
Applying a graphical procedure, found by reference to an appropriate almanac and the times and heights of high and low water, a navigator may precisely work out intermediate tidal heights and times. This then enables depth restricted vessels to pass into shallow waters supported by tidal water and accurately plot a position where a vessel may anchor and stay afloat.However plotting tides to this level of detail is a skilled, onerous and time consuming task. It is for many cruisers more for the world of merchant sailors. Moreover, tidal curves are often only available for major ports where most leisure vessels would have ample water, not in out of the way anchorages. In the real world, even if the information is available, few sailors would go to this level of detail.
Dealing with the different GPS conventions for describing a waypoint
GPS transformed the art of navigation forever, but there are subtleties of expressing a position that need to be understood. There are three different GPS conventions for describing a waypoint and it is important to know which convention you are using and the format of information you are being provided with from external sources.
Reducing the power draw of the vessels anchor light
The international COLREGS state that an anchored boat must display a round ball when anchored during the day and an all-around white light at night. The light must be an all-round white light which is visible for 5 miles for vessels between 12–50 metres (39–164 ft) and at least two nautical miles for vessels smaller than this. It must be placed in the forepart of the vessel or “where it can best be seen”. Maintaining these lights throughout the night draws a lot of power.
Understanding the Beaufort scale
The (nautical) Beaufort scale, or to give it its full name the Beaufort wind force scale, is an empirical measure that relates wind speed to observed conditions at sea or on land. The scale of wind forces are described for practical purposes by name, range of velocity, and classified from force 0 to force 12, or, sometimes, to force 17.
A simple way to keeping track of the tides
Sailing in tidal waters requires constant vigilance and quick maths to make the best use of currents. As the tide times are constantly changing and there are many distractions on a sailing vessel, it is easy to forget the tidal times or make an error of maths.
A tide and current predictor when cruising in unfamiliar waters
When crossing oceans and seas to new sailing destinations it is not easy to have arrival tidal data. Typically boats acquire local tidal data after landing.
Harbour information at your fingertips
Harbour information can be spread across pilotage and tidal books. Bringing the information together when required, takes some time to dig them out and hunt through them individually.
Clearing hazards with a danger bearing
Whether you are navigating by instrument or eyeball, what lies beneath the water is invisible in most places. And sometimes, the main concern of navigation is to avoid these hidden dangers such as extensive reefs or shoals. A good example that can be used to illustrate the problem is the Shingles Bank, on the western entrance to The Solent on the south coast of England. It is marked by several lighted buoys on the southeast side, or channel side, but none on the north side. Given its numerous shallow patches and rapidity of the tides, it has all the ingredients to put any vessel which might have the misfortune to come up on it in peril. But likewise there is deep water to the north with settled conditions and a good visibility cut between North Head Bank and the Shingles, keeping Hurst Castle open of its own width of Fort Victoria - see Solent Coastal Description. The problem with this is that the dangerous Shingles Bank lies close by which is mostly covered making it risky.
How to tell if you are on a collision course with another vessel
One of the most perplexing problems for newcomers to sailing is trying to assess converging courses of surrounding vessels and knowing how to judge who's going to cross whom. Sailing novices tend to be familiar with driving automobiles where it is easy to detect the possible risk of a collision with implicit reference to the background (e.g., the roads, the scenery, the landscape, etc.) At sea, when vessels are borne in water, the sea surface removes all visual clues obsoleting to a large part terrestrial instinct.