Final answer:
In a narrow channel, mariners should operate close to the starboard side for safety and to comply with maritime rules. Canoeists should paddle near the shore when going upstream for easier maneuvering against the current, and near the middle when going downstream to use the faster flow.
Step-by-step explanation:
When operating in a narrow channel, you should keep as close as is safe to the starboard side, which is the right side when facing forward. This is to avoid collisions and to allow for safe passing, as it follows the conventions set by maritime rules, similar to the rules of the road on land. The rule of keeping to the starboard side applies both to power-driven vessels and to non-powered vessels like canoes and kayaks.
In the specific context of canoeing, when paddling upstream, it is advised to stay near the shore because the water flow is slower there, making it easier to paddle against the current. Conversely, when going downstream, staying near the middle can be best because it allows you to take advantage of the faster current for easier travel and better maneuverability.