Well, thanks to Fenlander's fantastically good advice, I squeezed in a short engine-run-in session today over at Mersea Island... and what a day!
Set off from home about 09:30, arrived at 11:00. Did a quick recce and then brought the van down on to the hard standing. Inflated, kitted out, parked up van and got onto the water about 11:30. Everything was intensely easy although I can imagine during the summer months it's pretty hellish as there's not much space down there.
Boat ran sweet as a nut although the engine cut out twice which scared the bejaysus out of me the first time it happened... my back-up trolling motor managed to somehow disconnect the fuel line from the tank
Sun was shining, Blackwater estuary was like a mill pond. I'd been worried about getting cold, far from it, the sweat was lashing off me the sun was so hot. Out in the open water it was a little lumpy and I got airborne a few times
Fishing: pah - didn't get a nibble (not that I spent more than 5 minutes with my rod in the water)
Stats: about 20 NM and top speed just a smidge over 20 Kts on the GPS (iPhone and Garmin)
Boat performance: all good, however I've read about bowing floors and cavitation around the prop - I experienced the bowing floor which whilst annoying doesn't actually seem to matter... I didn't notice any cavitation or loss of power. One thing that did confuse me, the tacho seems to be reading funny, at WOT it was reading 2946 RPM but since I was doing nearly 20 Kts I assume to be the tacho wrong rather than the engine not doing 5000+ RPM.
I'm also really pleased with my instrument cluster and locating in the middle of the front seat is spot on for me. The 2 12v sockets a must for keeping the phone charged while running the RYA tracker. Also, tiller extension was invaluable!
I can now see why many people cut me down somewhat when I suggested I might like to ferry 4 adults and 4 kids around... once all my kit was on and I was busy making coffee, eating my sandwiches, fishing, etc. the boat felt an awful lot smaller than it does in my living room!
What a great first expedition in my SIB.