in game there do appear to be tide/current effects when surfaced... try this: center your rudder and check your heading, then try running for an hour or so without your helmsman following a nav plot, then check your heading again.
the heading deviation you'll observe might be weather related though... 'have to do some more experimentation to determine. also, these effects do not hamper your boat's course keeping ability when submerged. as well, your helmsman will always automatically compensate for "tidal/current drift" when following a nav plot, so this really only comes into play if you're using self-imposed manual navigation rules (like me!
)
cheers
hc