When designing a new Grav Survey Ship, I created a Military Jump Drive with squadron jump 3, capacity 5,000 tons. I put it on the Grav Survey Ship, then started adding various size fuel tanks until the GSV reached 5,000 tons. As soon as it hit 5,000, I got a design warning that the jump drive was too small for the ship size. I had to reduce the ship size below 5,000 tons to make the warning go away.