Cav....simulated cooling water on model vessels is always an eye catcher
........some of those gear pumps have acetyl gears & some have brass gears....& yes some are true centrifugal....now if you are running in salt or brackish water,,,
you may need to pump some clean fresh water into the suction side to get rid of the rubbish.... salt
or what ever at the end of each days running
Aquarium type shops have a multitude of relatively inexpensive brass or plastic manifolds & fittings for water transfer & aeration of fish tanks..........you could consider a fresh water flushing loop circuit using the installed pump within the vessel itself
......
If the pump is to run continuously ....it may be happier, cooler & less current draw on 6 Vdc also .......Derek