water on anchor lines

I'm sure the Anchor line / rope itself didn't use to be part of the mark. It certainly shouldn't be - Especially on reservoirs where when the water level drops, you occasionally have a mooring rope just submerged a few metres away from the actual mark and you can't even see it

Maybe it was just the underwater part that's not part of the mark - anyone sure on the current situation?

Yes, because:

Rule 18 applies when boats are about to round or pass a mark they are required to leave on the same side, or an obstruction on the same side, until they have passed it.  However, it does not apply

(a) at a starting mark surrounded by navigable water or at its anchor line from the time the boats are approaching them to start until they have passed them,

That's clear enough. You can't claim water until you have passed the committee boat, including its anchor. However if you were starting in light airs and foul current, passed the boat and then drifted backwards again, at that point the anchor chain might be an obstruction.

Mike,

My understanding is that the anchor / mooring lines form part of the 'mark of the course', and as such are treated the same way as the comittee boat itself.

There may be peeps out there who have another view.

To take the thread in a slightly different direction,  what's the penalty for hitting either end of the finish line (boat, anchor warp, or pin end buoy)? A 360 turn seems pointless if you've already finished... I'm off to the RYA site for a look-see.