You would need to look closely at depth of water, tides and the degree of slope of the beach concerned.
Realistically, you would want to land your agent at or near high tide so that the vessel can come as close inshore as possible. Since the Baltic, like the Mediterranean is nearly landlocked, I don't think it has much tidal range. You could try contacting the UK Hydrographic Office on that one.
Also try reading Paddy Ashdown: 'A Brilliant Little Operation', which has a good deal on the practical aspects of landing a raiding party from a submarine.
Hope that helps
Ann