[Sapphire]

Conventional wisdom will suggest diesel is preferred in larger vessels due to the torque these engines develop to move the heavier vessel. That's why most boats 36 foot or more are diesel. Many will argue diesel is safer as it does not readily explode should a leak develop.  Diesel tends to have more maintenance cost.  
I think that in this size vessel gas is fine, although you will find arguments on both sides.  Google it, you'll find lots of opinions.