Originally Posted by kas_1611
I have heard in Greece
you have to clear in at every single
harbour/port/marina on arrival regardless of how long you have been in country - needs to be confirmed but if true it sounds like a nightmare.
Sorry, that's nonsense. I suggest you read Greece | JimB Sail
for the facts.
One thing to consider is that if you are going to be in country for less than 30 days you need to report your presence, this is normally done by hotels when you arrive but if you are coming in by boat you will need to do this yourself - basically clearing in I suppose. If you plan to be in country for more than 30 days you have to register with the authorities as you may be considered to be resident and not just visiting. This does not affect your right to stay in any EU member state but you may need prove of ability to support yourself, residence etc.
Some countries (Spain an example) require that any EU citizen who stays longer than 90 days should register. This is for the purpose of tracking entitlements to host state benefits. Most other EU countries advise that this should be done if you intend to take up residence. There's no way of tracking such stays within the EU, and certainly none within Schengen.
This time, I suggest you read Time Abroad | JimB Sail
for the (slightly simplified) facts.