The centre I used to work at used to have one of these Kubota B1410 compact tractor £3750+vat | eBay
to launch and recover boats.
It had the grass tyres on it as shown and would pull the centres Ribeye 785's and 23' diesel launch up the slip way no problems in 4 x 4 mode even when they were green with slime. We had front counter weights on it or the front loader bucket fitted at all times in order to keep the front wheels on the floor and maintain steerage but no water in the tyres. I don't ever recall having to use the diff lock or low ratio to maintain traction.
We also had a pto driven brush which fitted to the 3 point hitch on the back to clean the slip way.
We got a towing bracket made to go on the 3 point hitch so attaching boats was really easy, just drive up to it and lift the hitch to lift the jockey wheel off the ground with out even getting off the seat!