A sailboat under power and sail
The rule that addresses how to indicate that you are underpower with your sails up is under Rule 25 Sailing Vessels Underway and Vessels Under Oars--International - it states(e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards.In Canada for inland waters there is a modification that indicates that:f) Notwithstanding paragraph (e), in the Canadian waters of a roadstead, harbour, river, lake or inland waterway, a vessel of less than 12 metres in length proceeding under sail when also being propelled by machinery is not required to exhibit a conical shape, apex downwards, but may do so.I think the same modification applies in US Inland Waters.I have only seen the inverted cone once with a large German Yacht visiting the North Channel of Lake Huron. Perhaps on the coasts it is more common.By the way, I always fly the Canadian flag from the stern and if visiting US waters I always fly the US flag from the halyard to the starboard spreader. My understanding is that this is a legal requirement when visiting a foreign country even though it is called a courtesy flag. I am also proud to fly the Canadian Power and Sail Squadron flag as well as my yacht club burgee.Edit: I just checked Chapman's 64th addition and it has exctly the same wording on page 140 as well as a picture (Figure 4-16). For those that are not familiar with it, Chapman's is a well known bible on piloting and seamanship that everyone should have.