Mark - obviously, my wording was not the best.  From each boat's perspective, they each believe they are on the other boat's leeward side, and, therefore, the right of way boat, and that, not being a leeward boat, the other boat is, therefore, a windward boat and required to keep clear of them.  The answer all depends on where you are sitting.  And if you are not on either boat it's really only 16 and 14 that keeps them apart. 

As an English speaker I alwats excerise  degree of wariness when anyone refers to the work of Mr. Webster...

The relevant Collins Dictionary nautical definitions are:
 to change the heading of (a sailing vessel) to the opposite tack 
to steer (a sailing vessel) on alternate tacks
(intransitive)  (of a sailing vessel) to proceed on a different tack or to alternate tacks.
Not to mention:
a course sailed by a sailing vessel with the wind blowing from forward of the beam

one such course or a zigzag pattern of such courses
a sheet for controlling the weather clew of a course 
the weather clew itself

the forward lower clew of a fore-and-aft sail

Under RRS Definitions: a boat changes from port to starboard tack at the moment she passes head to wind.

I think one issue is that nautical parlance has changed. When I first started getting shouted at by irate helmsman the proper terminology was 'to go about'. The crew was warned by the helm by a cry of 'ready about', followed by 'lee oh'.  The boat would to avoid the current then change tack. This might happen frequently, for instance when tacking along the shore. 

Tack has far too many meanings to be of any  use as a clearly defined word in the rules. 

Which will convince me better that you were anxious.

"I hailed Starboard. They ignored me. I hailed louder again shouting you need to tack too. They ignored me. I altered course"

"I wasn't sure if they saw me and I was anxious so I altered course"

Can you expand on this?

John, I am glad that the WASZP rules are working in practice.  I think that the wingfoils will go a different direction, with little or no limitations, at least in part because they are always in the standing position.  I think that should be up to the fleet decide and adopt in their class rules so we shall see as the class matures.