Here are a few that I browse...
- BoatDesign.net - Anything and everything related to boat design and construction, professional and amateur
- Panbo - The scoop on marine electronics
- Cruisers Forum - Mostly about cruising but some content on maintenance and DIY
- Wooden Boat Forum - Wooden boat building and maintenance
Readers, please post a comment and share any sites you have found useful in your project.