The current (unofficial) standard for ships is the track is 3m above the water. There are three other common arrangements - one is with the track 7m below water, one is for the track to be 3m below the water's surface, and you'll also sometimes see ships that use track at the water's surface.
All these systems (except the -3M canal system) assume the land (and rail track) is 3M above water.
Rationale:
The current standard (3m above water) arises from Vulcan's ferry system. This is described on his website (above).
The 7m below water is from the early days of Trainz, before invisible track. Early versions of Trainz would hide track that was underwater, so it was an easy way of hiding the track.
The -3M standard came about for the same reason, but was developed for canal boats, since the canals were not very deep.
And, track at water level is probably the most intuitive, so people unaware of the other standards generally use that.
As for ships, I have two drivable ships on the DLS, [FONT=Verdana, Arial]124060:1003:1 and [/FONT][FONT=Verdana, Arial]124060:1000:2. Both are set for track 3M above water.
Other ships are:
+3M track:
[/FONT][FONT=Verdana, Arial]60238:9044:2
[/FONT][FONT=Verdana, Arial]60238:9518:2
[/FONT][FONT=Verdana, Arial]60238:9519:1
[/FONT][FONT=Verdana, Arial]60238:9514:1
[/FONT][FONT=Verdana, Arial]60238:9027:2
[/FONT][FONT=Verdana, Arial]60238:9029:2
[/FONT][FONT=Verdana, Arial]60238:9050:1
[/FONT][FONT=Verdana, Arial]60238:9501:1
[/FONT][FONT=Verdana, Arial]60238:9502:1
[/FONT][FONT=Verdana, Arial]60238:9503:1
[/FONT][FONT=Verdana, Arial]60238:9508:1
[/FONT][FONT=Verdana, Arial]60238:9507:1
[/FONT][FONT=Verdana, Arial]60238:9025:2
[/FONT][FONT=Verdana, Arial]60238:9045:1
[/FONT][FONT=Verdana, Arial]60238:9038:1
[/FONT][FONT=Verdana, Arial]60238:9026
[/FONT][FONT=Verdana, Arial]60238:9028:1
[/FONT][FONT=Verdana, Arial]60238:9011:1
[/FONT][FONT=Verdana, Arial]84912:8488:1
[/FONT][FONT=Verdana, Arial]84912:50488
[/FONT][FONT=Verdana, Arial]78193:924:1[/FONT]
[FONT=Verdana, Arial]
-7M:
[/FONT][FONT=Verdana, Arial]36638:10048[/FONT]
[FONT=Verdana, Arial]36638:10038
[/FONT][FONT=Verdana, Arial]60238:9023
[/FONT][FONT=Verdana, Arial]78193:923:1[/FONT]
[FONT=Verdana, Arial]60238:9021
[/FONT][FONT=Verdana, Arial]60238:9022
[/FONT][FONT=Verdana, Arial]36638:9011[/FONT]
-3M:
[FONT=Verdana, Arial]36638:10015
[/FONT][FONT=Verdana, Arial]36638:9005
[/FONT][FONT=Verdana, Arial]36638:9004
[/FONT][FONT=Verdana, Arial]36638:9001
[/FONT][FONT=Verdana, Arial]36638:9007
[/FONT][FONT=Verdana, Arial]36638:9003
[/FONT][FONT=Verdana, Arial]36638:9000[/FONT]
[FONT=Verdana, Arial]
Water level:
[/FONT][FONT=Verdana, Arial]63290:102:1
[/FONT][FONT=Verdana, Arial]78193:925:1[/FONT]
Search tips on the DLS: set your filter to locomotives, and search for title = 'ship' or 'boat'; also try searching description for 'ship', boat', or 'water'. Check all Trainz versions.
Hope that helps!
Curtis