Port boat must yield, no rule requirement for Starboard to hail.

But, as has been stated by others, it's a good idea for Starboard to hail to avoid collision or having to alter course, thus costing them time in the race. Protest is the recourse here, but that doesn't always help if you've lost the race because of the incident.

Think about it...if there was a requirement for Starboard to hail all port boats, that means port boats don't even need to watch where they are going anymore since they'll wait to hear a hail from a starboard tacker when they're approached. There's no guarantee starboard is aware of the port boat, and even if they are aware, there's no guarantee a hail will even be heard.

If you are on port, you must spend the time/effort to be on constant vigil for starboard boats or else risk protest or worse.