Dive flag

The international code flag Alpha, a white and blue swallow-tailed flag, means "I have a diver down; keep well clear at slow speed". Every skipper who has passed a boat licence has learnt it. It is the only signal on the water that a boat is obliged to understand, and it has to be flown from the float, high enough to be seen above the swell.

The red flag with a white diagonal, the "diver down" flag of North America, is also widely recognised and many floats carry both. On the Moroccan coast fly the Alpha; add the red one if you like. Check the regulations page for what the Moroccan text requires of a spearo's signalling; wherever you are, a flag is what keeps a propeller off your head.

What matters:

• Size: at least 30 by 25 cm. A postage stamp on a stick is not seen from a boat in chop.
• A stiff flag, or one with a batten, so that it stands out in no wind instead of hanging like a rag.
• A mast of 40 to 60 cm above the float, rigid enough to stay upright when the float rolls in swell.
• Colours that stay: cheap flags fade to white in a summer, which turns the Alpha into a white flag.
• A firm mount on the float that does not fall over the first time you climb on it.

The flag comes with most floats. Judge the flag, not the float, and replace it separately when it fades.

30 by 25 cm minimum, on a 40 to 60 cm mast.

Rinse, dry out of the sun, and replace when the blue has gone pale. Check the mast fitting before each dive.