IALA Buoyage & Compass

Cardinal marks show the direction of safe water from the hazard. The mark is named for the direction of safe water — a North cardinal mark means safe water is to the North of the mark.

At night the shapes vanish and the rhythms carry everything. This table is worth owning cold:

Deployed FAST over new wrecks — precisely the dangers your chart doesn't yet carry: blue and yellow vertical stripes, upright yellow cross topmark, and an alternating blue/yellow light, one second of each. It is deliberately unlike anything else in the system. Response: widest practicable berth (a new wreck has an unknown least depth and a debris field), slow down, and check Navtex/NAVWARNs for the wreck's details — a mark you cannot explain is a prompt to check the warnings, not to sail on. Increasingly the FIRST marking is a virtual AIS aid to navigation, ahead of the physical buoy.

Every lateral mark's meaning is relative to the direction of buoyage: generally FROM seaward into rivers, harbours and estuaries, and around coastlines a general direction set by the charting authority — shown by the broad magenta arrow on the chart. Travel with it, Region A puts red cans to port; travel against it — every departure — and the same marks swap sides relative to your bow. Be most alert at junctions, around headlands, and at the places where two buoyage directions meet head-to-head and the laterals flip between one buoy and the next: those flip points are charted, briefable, and exactly where unprepared navigators ground.

Working rules: Compass → Deviation → Magnetic → Variation → True, adding east and subtracting west toward true ("Compass to True, add East"), reversed coming back. Deviation is entered with the heading you will actually steer. And the housekeeping that examiners ask because it is real: nothing magnetic near the standard compass — the phone, the speaker, the multitool left on the binnacle each write their own deviation card entry that no one has calibrated.

The gyro seeks true north — no variation, no deviation — but it has its own account: speed error (a function of speed and course, worst steaming fast on north/south headings at high latitude — corrected automatically on modern sets fed with speed and latitude, but only if the feeds are right), settling time after start-up (hours, which is why the gyro is never switched off in port lightly), and the brutal simplicity that when it wanders or topples it does so confidently — the repeaters follow it into the error. Hence the discipline: gyro checked against magnetic every watch, both checked against a transit or azimuth, and the three-way comparison logged. Three sources that agree are navigation; one source trusted alone is a story you tell the MAIB.