Monkton's Salamander

Congratulations, you made it back to the A.A.K.V.O. yacht with just a few gallons of fuel to spare! You jetted off to Staffa island where a suspicious fishing boat is anchored several kilometers away. It is suspicious because there is a large torpedo on the deck and the front of the boat says W.A.L.A. but there is no fishing company with that name. The must be a V.A.L.A. ship!

You also just learned that not only is the Staffa Island cave a base for A.A.K.V.O., it is also a research station for Monkton's Salamander, a rare salt-water cave salamander discovered by A.A.K.V.O. founder, Monkton Tuesdale. You must save not only the base, but the salamanders too!

You plan is to sneak up on the ship and place an explosive under the water-line to sink it. You'll use your dive scooter to go the 4 kilometers from the island to the ship undetected. The scooter can pull you at 4 mph and you'll be travelling at 50 feet under the surface. You have a 130 cubic-foot tank. How much pressure should you put in the tank to make it to the ship and back with 200 psi reserve?  Hint: you might want to use this website. Hint #2: your RMV rate is 0.65 cu-ft/min.