Flags need to be sufficiently large so that they can be seen and recognised from the far end of a start line.  For World and Continental Championships ISAF recommend that Flags be 36” x 24” (900mm x 600mm) but for most clubs a good compromise is 30” x 20” or 24” (760mm x 500 or 600mm).  The last set we bought for my Club cost around £ 650.00.  If you are buying a set of flags - get them to remove the 2nd Sub and 3rd Sub as these are not used but ensure the set contains a Blue, Orange and Black flag.  You might need two Oranges (each end of the start line) and maybe an additional 1st Sub (for your marklayer to run across the fleet with).

In some circumstances we have been lucky enough for one of our members to make up flags for specific purposes - Jury Flags, Press Flags etc.  These work well except if used on a RIB.  The problem is the stitching on letters does not last well if hurtling around on a rib - may be better to get a printed flag made for display on RIBs.  

At Ballyholme YC we have two “Good” flag sets which I look after.  One set is nearly all on poles ready to be used and the second set is rolled and kept in a carrierbag, numbers one end, main alphabet in the middle and specials (AP, Black orange Blue and 1st Sub) in the other end.

Bagged and ready to go