This isn't a real practical application for a compact tractor imo. I would consider a wheel loader or large forklift for this work. I would consider a one ton single wheel truck with a weighted bed and large motor and 4.00 + rear differential for towing.
If you still want a tractor for this type work consider an economy type 6140 Deere. This is a case for a high hp version for what ever frame size you settle on.
It takes lots of hp to pull a load up a long grade at a fast speed. This isn't what farm tractors are designed for, but some of the newer pickups and chassis cab trucks are perfect for this task.
Pretty well nailed it. A tractor in general is just not the most practical in this situation. You will be paying more upfront and more in fuel costs for a compact to a pickup truck and plus you can still drive the truck down the road. At 7500lb you can get a good new or used 2500 pickup to do all of your hauling. Unless you plan to use the tractor for a lot outside of just hauling the boats down the ramp I would get a pickup truck.