Weather patterns for a particular area, places to anchor and dock, safe passages through reefs. You can't always google the answer and much of it is gleaned from other sailors who used experience and their tools to figure it out.
Lots of this information is collated in Almanacks and pilot guides (eg. Reeds Natuical Almanac and the Shell Channel Pilot for UK sailors, plus the books from the Cruising Association and Royal Cruising Club). There's not a lot of incentive for an online version, as the information needs to be accesible offline for reference and in case plans change. However, there is a lot of information in apps: there's an iPad version of Reeds Natuical Almanac [1], Imray has a worldwide Tides planner app [2], and there are apps with charts from both the UKHO and Imray [3].
Lots of this information is collated in Almanacks and pilot guides (eg. Reeds Natuical Almanac and the Shell Channel Pilot for UK sailors, plus the books from the Cruising Association and Royal Cruising Club). There's not a lot of incentive for an online version, as the information needs to be accesible offline for reference and in case plans change. However, there is a lot of information in apps: there's an iPad version of Reeds Natuical Almanac [1], Imray has a worldwide Tides planner app [2], and there are apps with charts from both the UKHO and Imray [3].
[1]: http://www.reedsnauticalalmanac.co.uk/
[2]: http://imray.com/tides-planner-app/
[3]: http://www.yachtingworld.com/blogs/elaine-bunting/testing-ip...