Then the bowsprit got mixed with the rudder sometimes: A thing, as the Bellman remarked, That frequently happens in tropical climes, When a vessel is, so to speak, "snarked."
He acknowledges a risk (which could be avoided with a map) in a dismissive way. When a sailing ship traveled into equatorial climes they might get too far from the trade winds and be stuck in the doldrums with no way out. A map could help avoid wandering into the equatorial climes and avoid being stuck.
