When I write sea stories, I have by me a chart, or series of charts,of the waters I am describing. I don't think you need them to follow the story, but I have had some enquiries about places, and charts, and a request to provide a map showing some of the more obscure places I name. I am not sure if that's possible. But there is a web-site, www.visitmyharbour.com, which provides online charts, mainly of harbours, but also of rivers. These show names which will not show up on Google maps or atlases. Access is free, though a small subscription does give you access to better, zoomable, charts and, I think, of wider areas. For the most part, I don't think you need more than Google, but they are there.
Proper charts are expensive; my Imray Thames Estuary chart, which covers not just the Thames, but the coast from North Foreland to Felixstowe and the River Deben was about £18, $27.
But if you read my stories and can't find somewhere - do feel free to email me and ask!