I went on a night exercise with the Pathfinder Powerboat club several years ago, www.ppc.org.uk
In a word it was brilliant.
Very well organised with detailed briefing beforehand. Mixture of RIBs and Powerboats. We formed into two groups and went around a planned route with stop-offs and radio checks along the way. Everything was cleared with the coastguard and Queens Harbourmaster before hand although that did not stop Portsmouth sending out a launch to investigate our activities! Some interesting navigation such as following sector lights into Fishbourne and we set off a white flare as part of the exercise.
I see that they are running the same event this year on 13th October and it would be worth the £30 membership for this alone.