Hi Mark
Standard configuration for sailboats at night is bow red/green 112.5 degrees from centre line. Stern white facing aft 135 degrees and mast head all around white (this is also an anchor light at night) .
An acceptable alternative is tricolour at mast head but not common in Eu or Americas (some Catamarans favour tricolour at mast head)
Hi Ian,
Just to clarify, if a sailboat is not using a tricolour light at the masthead, they will show port and starboard red/green sidelights illuminated from right ahead to 112.5 degrees, or 22.5 degrees abaft the beam on their respective sides. The stern light is visible from 22.5 degrees abaft the beam on each side to right astern, a total of 135 degrees. The cut off points of 22.5 degrees abaft the beam on each side helps you and passing vessels at night to determine whether they are overtaking or crossing vessels within the meaning of the Colregs.
The tricolour light at the mast head takes over the functions of the three lights referred to above, and with the same cut off points and should not be shown in combination with the foregoing three lights.
The all round white light you referred to, part of the fitting containing the tricolour on my boat, is intended as an anchor light, and should not be shown while underway.
Located on the mast, usually a little less than about half way up and often combined with a deck flood light, is a white steaming light. This light has the same cut off points as the side lights, and is visible from 22.5 degrees abaft the beam through forward to the same point on the other side, a total of 225 degrees,, and should only be shown while your boat engine is being used either on its own or in addition to the sails