If you are using motor and sail, rules of navigation say you declare yourself as 'sailing'.
No if you using an engine for propulsion you are a power driven vessel
Col Regs Rule 25(e)
What are you talking about? That's the rule for a sailing vessel and is about lighting (well, specifically, displaying an inverted cone).
If you are both motoring and sailing you displaying signals indicating both, so that other vessels know you are restricted in your ability to manoeuvre. So a tanker flying a Skysail (or equiv) would very reasonably indicate on their AIS that they were under sail.
No you wouldn't. The colregs are clear - if you are using an engine for propulsion you are not sailing, whatever sails you may have hoisted. You need to exhibit the day sign for motor sailing or the correct navigation lights at night to indicate to other vessels that you are not sailing. Also if fitted with AIS you need to display the correct information.
The navigation rules that apply to you are those for motor driven vessels.
So why did you cite a colreg for a sailing vessel?
You are wrong, you know. This is your colregs 25(e) (e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward .
Anyway, we aren't talking colregs, this was AIS.
I strongly suspect that the incorrect code was entered in the AIS for the tanker, but the statement that "A tanker is too big to be sailing" is also wrong. A tanker can be motor sailing.
Nope you're still wrong I'm afraid
Rule 25(e) defines the point at which a vessel ceases to be a sailing vessel (obeying the rules for sailing vessels) and becomes a motor vessel (obeying the rules for motor vessels). That definition is also in rules 3(b) and 3(c).
Even though AIS has not been formally integrated into the COLREGS it is used as its name implies for identification of ships out of sight of each other and therefore needs to show the correct information and in this case should show either moored or underway. Not underway by sail.
If a tanker is motor sailing it is not sailing - they are very different situations and would be handled differently.
As far as I am aware there is no current technology that would allow a 125,000 dwt vessel to proceed under sail alone it will always need to use its propulsion engine and will therefore be a motor vessel.
http://www.mar.ist.utl.pt/mventura/Projecto-Navios-I/IMO-Conventions%20(copies)/COLREG-1972.pdf
