Bos,
Oostende Lines operated their jetfoils with the upper deck closed during the quieter times, OK the company folded but so did a few cross channel operators brought about by the opening of the tunnel.
Even if passenger numbers are in their 10's, just one sailing, if that's what it's called, a day, in the opposite direction that the ferry is travelling at that similar time, might break even or better.
Yes, a big investment but as big an investment as flying machines?
Perhaps a comparison to Penzance to Scillies might be Southampton to Channel Islands, SOU has a less than lengthy runway hindered by the M27 motorway passing by one end of it, not far down the road is BOH airport, better runway, better most things but ...... certainly in the days of BIA/Air UK, probably now FlyBE and other(s), SOU to CI is/was literally like a bus service whereas BOH would have minimal flights per day/week and why? ..... Because SOU has a train station whereas the pax get off the train from anywhere in UK, walk a few yards, and check-in for their flights.
My point is that St. Just's S61 operation may become the BOH of Cornwall, whilst not mainline NQY has a rail connection thus I would envisage ISC traffic from/to NQY increasing moreso than St. Just.
Just making the point
