Since you're only there for the day, I wouldn't recommend driving out of town.
Playa Kalki is a 45min drive one way after you get a car rented. And the downtown area is really congested when ship(s) are in port. So you could easily burn 2 hrs. + just getting there/back. If you decide to try it Ocean Encounters West does have a good facility there with showers/lockers. But PK is probably the
best shore dive on Curacao.
The Dive Bus is a good option (one that I also recommend often) but they don't seem to offer their normal service to shore dive sites for
Cruise passengers - if I'm reading this correctly:
The Dive Bus - Diving Curacao for cruise ship passengers
Note that you have to take a cab there, they don't pick up at the cruise port.
If you have any questions, PM Suzy from the Dive Bus: [user]TheDiveBus[/user]
I think I would try the Tugboat. It can be done as a shallow dive (the boat itself is in 20') or start the dive deeper around the point and do your safety stop checking out the boat. (it's pretty small) There's a wall around the point that my friends said was loaded with eels.
It's probably close enough to the cruise port that a cab ride wouldn't be too expensive - maybe $25? each way or so. There's an on site diveop there for tanks. One thing to know about anywhere you shore dive - there's often a diveop on site and you pay a small fee to use the facilities - under $5 US IIRC.
It's possible your cruise line may also take divers to the Tugboat. From what I've read the cruise excursions can be pricey. There also could be a lot of snorkelers from a ship there. We watched as a cruise tour boat moored and dropped over 50 snorkelers near the Tugboat. It's a popular snorkel because you can see a wreck at 20'.
I think the previous poster missed the part that you're on a cruise. Once you leave Willemstad the roads get worse and street signs become harder to find. If you do decide on Play Kalki stay on the North road when it splits outside of town, it's faster to Westpunt but less scenic. The other road goes through small towns along the water so it's slower. There's also not a lot of eating options anywhere except Westpunt on the drive back on either road.
Are you solo? It's likely you won't find anyone to dive with at either the Tugboat or Playa Kalki. So maybe the DiveBus is the best option.