I suggest that the boat is some sort of military surplus, retrofitted to look like an innocent civilian, non-threatening craft. Seems to me that we have a lot to choose from from our navy, since most of it seems to be moth balled/headed for the scrap heap these days. Seriously though, the biggest problem would be finding places to go into harbour to refuel & get more food and water. Not to mention ammo, I figure most countries won't be very excited about the prospects of us running rampant through all the gun shops, asking "Got any incendiary .50 BMG? We need like 4000 rounds of it!"
Also, how the hell would we finance it? Think it would fly to ask for 10% of the total value of the ship & cargo as a reward for finding it and bringing it back? I think quite a lot of folks who operate the shipping lines would scream "Piracy" again when they hear that...