Navigation: charts, buoys, tides and night sailing.

Where navigation is taught

The RYA's Day Skipper shorebased course covers coastal navigation and pilotage, chartwork, position fixing, course to steer, tides, meteorology, collision regulations and an introduction to lights for night cruising. US Sailing has a separate Coastal Navigation certification on its ladder. Use this page as background before a course like those, not as a replacement for one.

Charts

In the US, the key reference for reading a chart is U.S. Chart No. 1, published by NOAA and the National Geospatial-Intelligence Agency. It explains the symbols, abbreviations and terms used on paper charts and on electronic chart displays.

Some commonly taught chart facts (how chart scale relates to detail, using the latitude scale to measure nautical miles, and which tidal datum US soundings refer to) appear in our research only from an exam-prep source that we could not confirm against an official one, so we leave the details to your course and to Chart No. 1.

Variation and deviation

A magnetic compass does not point to true north, and the error comes in two parts:

Variation

The difference between true north and magnetic north. It depends on where you are and changes over time. The chart's compass rose shows it, along with its annual change.

Deviation

The difference between magnetic north and what your compass reads. It depends on your boat and on its heading, and comes from the boat's deviation card.

savvy navvy gives the memory aid for converting a true course to a compass course: add westerly error and subtract easterly error ("error west, compass best; error east, compass least"). It also notes that GPS and gyro compasses report true north and are not affected by deviation, but you should check whether a given device is displaying true or magnetic.

IALA buoyage: regions A and B

The colors of port-hand and starboard-hand marks depend on which of two IALA regions you are in. According to the IALA Maritime Buoyage System document (as hosted by Irish Lights):

"Port" and "starboard" here follow the direction of buoyage, which is usually the direction a boat takes when approaching a harbour, river or estuary from seaward. In US waters the Coast Guard sums this up as "Red Right Returning": keep red aids on your starboard side when returning from sea, and aid numbers increase from seaward. The rules for System A came in 1977 and for System B in early 1980, and an IALA conference in November 1980 combined them into one system with regional boundaries.

Marks that are the same everywhere

• Cardinal marks are yellow and black with two black cone topmarks and white lights. Their light rhythms: North continuous quick flashing, East 3 flashes, South 6 flashes plus a long flash, West 9 flashes.
• Isolated danger marks are black with red bands and two black spheres on top.
• Safe water marks have red and white vertical stripes and a red sphere on top.
• Special marks are yellow.
• The Emergency Wreck Marking Buoy has blue and yellow vertical stripes, a yellow cross topmark and an alternating blue and yellow light.

On the US Intracoastal Waterway, the Coast Guard says yellow triangles are kept to starboard and yellow squares to port. It also notes that tying a vessel to an aid to navigation is illegal.

Tides and currents

NOAA describes tides as long-period waves driven by the moon and sun. The tidal range is the height difference between high and low tide. NOAA defines the tidal currents this way:

• Flood: current flowing toward land.
• Ebb: current flowing toward the sea.
• Slack water: the short period of near-zero flow between them.

NOAA says tidal currents are strongest around full and new moon (spring tides) and weakest around the first and third quarter (neap tides), and that near estuary entrances, narrow straits and inlets they can reach several kilometers per hour.

A rough guide for tidal height is the Rule of Twelfths: from low to high water, the tide rises by about 1, 2, 3, 3, 2 and 1 twelfths of the range in successive hours. Safe Skipper stresses it is only approximate, and that local geography (it gives the Solent as an example) can distort it. For planning, use the official tide and current predictions for your area.

Night sailing considerations

Lights

Under COLREG Rule 25 (as published by a maritime-education site, since the official text did not load during our research), a sailing vessel underway shows sidelights and a sternlight. On a boat under 20 m these may be combined in one lantern at or near the masthead. A sailing vessel under 7 m that cannot carry these lights must have a white torch or lantern ready to show in time to prevent a collision. A boat under sail that is also using its engine must show a cone, point down, by day; the Coast Guard's amalgamated rules text says vessels under 12 m are exempt under the US Inland Rules. The RYA advises carrying navigation lights that meet the COLREGs for your boat's type and length, with spare bulbs or fuses, an emergency backup and several powerful torches. Lighting rules are legal requirements, so check the current rules that apply to your boat with your local authority.

Night vision

Sources disagree on how long your eyes need to adapt to the dark:

Both advise avoiding white light and using red light to protect it.

Crew and planning

• Stay attached. The RYA advises clipping on with tethers sized and attached so crew cannot go overboard, and the skipper checking everyone's lifejacket.
• Run a watch rota covering both helm and lookout (RYA).
• Pick waypoints you can identify in the dark, and sail defensively around large vessels (RYA).
• Reduce sail before dark, never leave the cockpit at night, especially when alone on watch, and wake the skipper for any concern (experienced skippers quoted by Yachting World).
• Arrive at unfamiliar places in daylight, and consider AIS beacons or PLBs for crew (Yachting World contributors).

The RYA Day Skipper practical includes night sailing to practise pilotage in the dark. For weather, NOAA Weather Radio broadcasts continuous National Weather Service information in the US on seven VHF frequencies between 162.400 and 162.550 MHz. Right-of-way rules are on rules of the road, and electronics on electronics.