Add "Boat Operator" to your "Basic Auto" Drivers License
The boat license will be pro-rated according to the time left on your driver license (you just pay a percentage relative to the amount of time left on their 4 year basic auto towards the Boat upgrade).
Example:
If you have 1 year left on a Basic 4 year auto non-photo, the upgrade cost would be $4

Link for NJ Division Of motor Vehicles

NJ Division Of motor Vehicles General Customer Information
1-888-486-3339
toll-free in New Jersey