I’m reading this question as getting the train from Southampton to Portsmouth for the ferry. Most off-peak hours this will be quickest using GWR which normally arrives in platform 1, the north side of the station. The ferry terminal is effectively across the end of the station but to seaward, perpendicular to the platforms. If you are at the very front of the train at Portsmouth Harbour it is very near the ramp down to the terminal which is at a slightly lower level than the station platforms, then there’s a bit of doubling back and another ramp to the ferry boarding point, slope is dependent on the tidal state. I don’t think it’s quite as far as the above poster reckons, I’d say around about 150m max including the short distance from the front of the train.
Journey planners should include adequate transfer times, I’d have thought. Selecting a via point of Portsmouth Harbour, they suggest GWR at xx-05, arr xx-52, ferry departs xx+1-15, around 22 or 23 mins to transfer.
May be worth giving Wightlink a ring in case they provide assistance within the terminal.
