Torpedo in a Lifeboat

Congratulations, you successfully placed the explosive on the underside of the V.A.L.A. ship! The ship sank and everyone made it off safely. All the lifeboats started rowing east toward the Island of Mull. But then one lone boat veered off and is now headed toward Staffa island! You sent a quad-rotor over it for reconnaissance and you have spotted the torpedo in the boat! They must be trying to get closer and launch the torpedo from the small lifeboat!

You can see the boat is sitting low in the water due to the weight of the Mark 23 torpedo. That gives you an idea. If you drop sand into the boat, it should easily sink! The boat's capacity is 25 men. You assume the average man weighs 200 pounds, and you want to drop enough weight to exceed the boat's capacity by 10%. The sand on Staffa island weighs 130 pounds per cubic foot. How many cubic feet of sand should you drop on the boat to sink it?