Without a boat; lacking boats or the ability to travel by boat.
From 'boat' + '-less' (Old English suffix meaning without or lacking), a straightforward negation creating an adjective.
The '-less' suffix is incredibly productive in English, and you can attach it to almost any noun—'boatless' would describe someone without access to boats, which was the condition of most of humanity for most of history.
Complete word intelligence in one call. Free tier — 50 lookups/day.