You can put it where you like, but my understanding is that it SHOULD be at the mainmast head. Failing that, at the starboard spreader if you are not flying a courtesy flag. Problem comes if you want to fly a courtesy flag then that should be at the starboard spreader & the burgee gets demoted.

In general, this is not a problem, but if you have an Admiralty warrant for a special ensign, then the club burgee has to be in the senior position; which is at the masthead. Or so I have been told! I put mine on a garden cane to get it clear of the windex, lights & aerial. Searush is a ketch too.