The ships used in the 400s in Britain would not have had masts and sails. They'd have been like the
Sutton Hoo ship--the hull would have been very like a Viking longship, (lap strake construction with a starboard and keel, but no mast footing) with
thole pins instead of oar holes.
Ways you could tell which way they went:
- The river is narrower than the ship is long so it can't turn around. This would make it more likely they went upstream. (But in that case, they probably wouldn't have gone so far up the river they couldn't turn around.)
- The locals know there are rapids up stream so even if the raiders went that way, they'd have to come back or port the ship around the rapids (or they can't port the ship because the river peters out).
- The river gets very shallow upstream (less than three feet deep) so they'd have to go downstream or turn around.
- It's quiet out and they haven't been gone that long. In which case, someone might be able to hear oars splashing up or down stream.
- It's quiet out and the person KNOWS the ship has just left and
can't hear oars, which would make it more likely they were drifting down river with the current.
- The river is very straight, it hasn't been long since they left, in which case the person can just
see them.]
- Climb a hill or a suitable tree and have a look up and down stream.
- Walk, run, or ride a horse up or down stream looking for them.
- The raiders are raiding again and the person can see smoke up (or down I suppose) stream.
- It's been a while and a survivor of another raid appears to tell you which way they went. Or someone who saw them go by.
- The person knows the raiders loaded their ship so full of loot that it's more likely they went downstream to go home rather than upstream to overload the ship with more loot they can't carry.
[Al X.--the old Norse word for steering board was "starboard" (hence starboard side of the ship) and the loading side of the ship was called the larboard side. Later larboard was changed to port. And yes, the starboard was--in all cases we know of--on the right side of the ship (Vikings TV show be damned.)]