Comment by dredmorbius

Both entrances to the tunnel are from relatively sheltered bays / inlets. Swells would be fairly modest generally, though wave mitigations might still well be a concern.

See map: <https://en.wikipedia.org/wiki/Stad_Ship_Tunnel#/media/File:S...>.

That said, I'm not finding any discussions of the hydrodynamics of the tunnel, other than this: "Ship Manoeuvring Study of a Vessel Transiting a Ship Tunnel", by Andrew Ross, Anne Bruyat, Leiv Aspelund, Vahid Hassani, and Abushet Simanesew (2024) <https://asmedigitalcollection.asme.org/OMAE/proceedings-abst...>.