You should have a look at
http://www.astra2d.co.uk .
According to the official Astra 2D footprint map,
http://www.ses-astra.com/satellites/beam/beamByXpr.php?pos=2&sat=ASTRA+2D&xpr=41,+42,+43,+44,+45,+46,+47,+48,+49,+50,+51,+52,+53,+54,+55,+56
Gothenburg is roughly on the same contour as Lund, further south. Various people on the astra2d site have reported that 1.8 m is enough in Lund (and also Copenhagen) with the right LNB and some tweaking.
I'm on the other side of ferry route from you, (in Aalborg, DK) and I get BBC 24/7 with a 1.5m dish. So I would guess that 1.8 m is the absolute minimum; the next size up, if you really want to be sure of reception. ;) The quality of materials (dish, LN
is important, in any case.
(BTW, for me the vertical transponders are much stronger than the horisontal ones after LNB skew adjustment. Most in the CPH/Lund area seem to have the opposite problem.)