What are the weights (including trailer)?
Good chance the 1/2 ton has enough
propulsion power to get the
boat moving (ie: tow rating) but the more common issue is to run out of payload. 1/2 ton trucks have wildly varrying payloads from as little as 1300lb to upwards of 2500lbs depending on how they are spec'd.
Ideally, you want 12-15% of the
trailer weight sitting on the ball.
So if the loaded
trailer weighs 10,000lb, I would want 1500lb of payload available for the trailer but you also have to account for passengers, cargo in the truck and any bolt on items (bed caps, running boards, etc...). A lot of 1/2 ton trucks will run out of payload before hitting the tow rating.
How often will you be towing and what percentage of miles will be towing? If you are at 8-10k lbs and the truck is primarily for towing, I would go 3/4 ton. If it's usually a few miles to the local launch and maybe 1-2 trips of a few hundred miles but most miles will be running empty, I would look at a 1/2 ton with suitable specs.