After a transatlantic passage you make your landfall and observe a buoy: red and white VERTICAL stripes; spherical (pillar/spar) shape; single red sphere topmark; light characteristic Iso white, Oc white, LFl white, or Mo(A) white. What is this mark and what does it mean for your navigation?

A. SAFE WATER MARK (also called mid-channel mark or fairway mark). Colour: red and white VERTICAL stripes — the stripes distinguish it from any other IALA mark. Topmark: single RED SPHERE. Light: Iso (isophase — equal on/off), Oc (occulting — light more than dark), LFl (long flash) or Mo(A) (Morse code A: dot-dash) white. Meaning: safe water exists ALL AROUND this mark — it marks the centre of a channel, a mid-channel position, or a landfall approach point. Action: you may pass on EITHER SIDE. The mark confirms you are in safe navigable water. In landfall use: it marks the outer approach to a harbour or channel — you steer towards it to confirm your landfall position, then use it as your datum for the channel entry.

B. Red and white vertical stripes indicate a port lateral mark. Red marks are always port hand in IALA A — pass with this mark to port.

C. Red and white stripes indicate a special mark used for racing or survey areas. No navigational significance — pass on any side and ignore.

D. A spherical buoy with single sphere topmark is an isolated danger mark. The red colouring confirms a danger beneath — approach from the north and pass to the north.

A. IALA System A — Red to PORT when entering harbour (proceeding from seaward). Red can buoy on your port side means you are on the starboard side of the channel, heading seaward (leaving harbour). To re-enter, you would keep the red buoy to PORT. Rule: In IALA A: RED = PORT = entering harbour (coming from sea). Green = Starboard = entering harbour. Memory aid for IALA A: "Red to Port Returning." The question states the red buoy is to port — therefore you are ENTERING HARBOUR correctly, keeping the channel to starboard. Pass the red buoy keeping it to PORT (leave it on your port side). In IALA B (Americas, Japan, Philippines, Korea): colours are reversed — red to starboard entering.

B. In IALA A, red buoys are always on the starboard side of the channel. Pass the red buoy keeping it to starboard — it marks the starboard side of safe water.

C. IALA A and B are interchangeable in UK waters. The MCA has adopted a combined system since 2015 where red marks starboard in all UK harbour approaches.

D. Red can buoys are cardinal marks indicating danger to the north. Pass to the north of the buoy regardless of the direction of travel.

A. NORTH CARDINAL MARK. Topmark: two cones BOTH pointing UP (like an arrow pointing north). Colour: black over yellow (black upper, yellow lower). Light: white VQ (very quick) or Q (quick) — uninterrupted. Meaning: safe water lies to the NORTH of this mark. The mark indicates a hazard to its south — the safe side to pass is to the NORTH. Action: pass the mark to the NORTH — i.e., keep the mark to the SOUTH of you as you pass. In this scenario the buoy is bearing 358° (nearly north), so you are approaching from the south — the mark is warning you of danger to your south; you are already in the safe water north of the mark. Monitor: do not pass to the south of this buoy.

B. North cardinal marks are passed to the east. The topmarks and colour confirm this is a north cardinal but the passing convention is to leave it to port when heading north.

C. Two cones pointing up indicate an isolated danger mark. Pass on either side with caution as the danger is directly beneath the buoy.

D. VQ white light with black/yellow topmark indicates a special mark. These do not indicate hazards and may be passed on any side.