So I know this doesn't answer your question, but may help and save you some money. There is nothing in the colregs that says that any anchor light needs to be at the top of the mast, and in my opinion it's a bad place for any anchor light. It's high above the line of vision. The regs says that it must be an around white light in the forepart of the boat. So get a white solar lantern and hang it from a halyard. I tie a down haul to a solar lantern, use a halyard to pull it 8-10 feet from the deck and tie the down haul to the bow. The lantern will be suspended away from the mast so it doesn't bang. It also lights up the deck for even more visibility.
Rule 30 (Anchored vessels and vessels aground)
(a) A vessel at anchor shall exhibit where it can best be seen:
(i) in the fore part, an all-round white light or one ball;
(ii) at or near the stern and at a lower level that the light prescribed in subparagraph (i), an all-round white light.
(b) A vessel of less than 50 m in length may exhibit an all-round white light where it can best be seen instead of the lights prescribed in paragraph (a) of this Rule.
(c) A vessel at anchor may, and a vessel of 100 m and more in length shall, also use the available working or equivalent lights to illuminate her decks.
(d) A vessel aground shall exhibit the lights prescribed in paragraph (a) or (b) of this Rule and in addition, where they can best be seen:
(i) two all-round red lights in a vertical line;
(ii) three balls in a vertical line.
(e) A vessel of less than 7 m in length, when at anchor, not in or near a narrow channel, fairway or anchorage, or where other vessels normally navigate, shall not be required to exhibit the lights or shape prescribed in paragraphs (a) and (b) of this Rule.
(f) A vessel of less than 12 m in length, when aground, shall not be required to exhibit the lights or shapes prescribed in subparagraphs (d)(i) and (ii) of this Rule.
