Thanks Fraser, for the additional info.
I was in Southampton on business today, so was able to visit the boat afterwards.
I have two chart plotters, one of which is linked up to the radar and VHF. The other is a standalone back-up but still built-in.
When I went for the "test drive" with Scorpion on hand-over day, I was reading the speed off the back-up. On looking at it this afternoon, I note that the units of measurement were statute miles - not knots!
Regrettably, I fear that we were only doing a pedestrian 43.2 kts and 49.7 MPH.
Of course, there was 80 gallons of fuel and 3 people on board, so I ought to be able to get 45 kts or so, when some of the fuel has been used, but it's not quite as whizzy as I had first thought.
Following this through, the maximum tidal rate in the Lymington area at 11:00 BST on 20th May (it was dead on a neap tide) would have been 1.6 kts, so I ought to be able to get at least 41.6 kts, if there is no tide running, more when there is less fuel and the engine has properly loosened up (I still believe that it should be run-in to an extent). I reckon I got just under 40 kts, on slack tide this weekend, so it still looks like there has been a loss of performance, albeit not quite so dramatic as I had first thought!
Having discovered that it is "Round the Island" and the restart of the Volvo Ocean Race this coming weekend, I shall leave it a week or two, before visiting the Etec engineer. This should also allow me to use some of the existing oil, before I have the engine modified to accept "XD 100".
Thanks for all your input.
Best wishes,
Chris.