As in all ports now all quays are fenced off, no access.
Best locations are therefore along the canal from Ymuiden to Amsterdam.
For instance near the ferry at Buitenhuizen.
Or go to Ymuiden (also called Velsen) were you can see the ships at the three locks.
At Ymuiden you have also good locations to park your car and simply wait for the passing ships.
But be prepared to see nothing in four hours and than four vessels in one hour!
Visiting cruiseships you can find here:
http://www.ptamsterdam.nl/index.php?site=cruises&hc=cruisekalender