My uncle-by-marriage, Bruce, and my uncle (my mother's brother) Reuben took the sub out in the ocean one day.  Bruce was in the sub, and Reuben was in the boat.  Big, Big mistake.  Reuben worked at a car factory where he painted cars, and I strongly suspect that over the years, he's inhaled entirely too much paint.  Anyway, Bruce told Reuben that if he surfaced and waved, that meant to cut the engine, because Bruce would be experiencing some kind of problem.  He also told Reuben to go very, very slow, since this was the trial run.  At the end of about two hundred feet of nylon rope, Bruce submerged.  Reuben, being totally ignorant of things nautical, thought the boat (a 13'3" Boston Whaler) wasn't moving at all, so he cranked up the rpm, and was happily cruising along.  Meanwhile, underwater, Bruce realized to his horror that he was moving very quickly indeed, and visibility was quite limited.  He pulled up on the stick in order to surface.  The speed of the sub was such that it was very difficult to keep it above water even with full ascend on the bow planes.  He managed to stabilize it long enough to get his head above water and started waving at Reuben like crazy. Reuben (I wish he had a different name!), eventually saw Bruce broaching the surface and waving, but being the total space cadet that he is, he completely forgot that he was supposed to stop.  He later said that he thought Bruce was telling him to go faster, and he was quick to oblige.  He put the Johnson outboard at about half-throttle.  Now, without towing anything, Bruce's Whaler could get up to almost 40 mph.  The sub imparted a considerable drag, but at half throttle he was probably traveling at about 15 mph.  That doesn't sound like much, but remember this was a wet sub, open to the water.  The small windshield didn't offer much protection and actually directed the powerful flow of water directly into Bruce's face, threatening to rip his mask right off his face.  No doubt almost drowning himself cursing at Reuben underwater, he managed to once again surface, waving as if his life depended on it (it did).  Reuben once again saw Bruce's frantic waving and proceeded to fire off all three of his operating brain cells.  Deciding that Bruce wanted to go faster still,  he gave the engine full throttle.  Bruce went down again.  The water was rushing at him with terrible force, flattening his mask and causing his snorkel to flop around and clobber him repeatedly on the side of his head.  The regulator was in danger of being pulled right out of his mouth.  The boat's prop was cavitating badly, and the sub was surrounded by a dense field of bubbles.  Combined with the poor visibility, this effectively blinded Bruce; he couldn't even see the nose of the sub.  He yet again struggled to surface his craft.  Now the sub was bucking like an unbroken mustang.  It would almost leap out of the water, then come crashing down, burying its nose in the water and going under again. The bow planes were never intended to withstand such force and bent back against the sub's hull, becoming completely useless.  Bruce was doing everything he could, that is, he was hanging on for dear life, cussing a wet blue streak, and mentally choosing which of Reuben's bones he would break first if he lived through this.  After several minutes of his underwater Nantucket sleigh ride, the nylon rope parted from the strain, and the sub came to rest.  Eventually, Reuben realized that the sub was no longer at the end of the line, and put about to pick up the half-drowned Bruce.  The most amazing thing about this is that Bruce didn't pound Reuben into a pulp (really!).  He probably thought that anyone as stupid as my uncle Reuben wouldn't be worth the trouble.  Reuben didn't think he'd done anything wrong, and couldn't understand why Bruce never let him into his boat again.  (True story!)