Men who put to sea in ships are subject to cruel ironies. The sea, as the saying goes, careth not for any man.

But the cruelest irony of all is reserved for those who lose their ships and are adrift in a lifeboat on a bottomless blanket of blue.

Surrounded by unlimited water, their deepest peril is thirst. "Water, water everywhere," moaned Samuel Coleridge in the Rime of the Ancient Mariner, "nor any drop to drink."

Sea water contains about 35,000 parts per million of salt, a circumstance that renders it unfit for sustaining human life. Salt in those quantities steals liquid from the body, which means the more you drink the thirstier you get.

Along comes the Navy with a last-ditch effort to build a machine that a humble seaman can use on his own power to make sustenance out of salt.

"They had been working on this project for about eight years before they gave it to me," said Joe Pizzino, a civilian chemical engineer with the Navy in Annapolis.

"They came up with a machine that weighed about 50 pounds and worked about 10 minutes for every five hours you pumped it. I thought, 'What a dog.'"

His boss at the Navy told Pizzino and his colleague, mechanical engineer Wayne Adamson, "I'm giving you guys $40,000 to either make it or break it." That was seven years ago.

This year they made it.

Independent seamen the world around should light up at the news of the hand-operated reverse osmosis desalinator now undergoing final testing in the lab where Pizzino and Adamson work.

This gizmo is about 2 1/2 feet long, weighs about 12 pounds and is capable of producing a little over a gallon an hour of drinkable water out of sea water, with nothing but elbow grease to power it. Last week I pumped it and drank it. It works.

Desalination is a process that has come of age. Today there is a huge, fuel-powered desalting plant in Saudi Arabia that makes 8.2 million gallons of fresh water a day out of sea water.

Navy ships use distillation processes to provide all their fresh water at sea.

But until now, no one has created a simple hand-powered rig that worked.

The problems are size and pressure. Distillers (stills require space and fuel. Solar power is feasible, but space required for a solar still is immense.

The other desalination process involves forcing sea water through a membrane that separates the salt from the water. Extreme pressure is requied to run this" reverse osmosis" desalinator.

The demand for pressure was the dilemma that held back development of a hand-powered rig. Pizzino and Adamson went on a search to find someone who could produce a hand pump that would provide the 800 to 1,000 pounds per square inch needed to run a membrane-type desalintor.

They found Seagold Industries in British Columbia.

"It was just luck," said Pizzino. "We stumbled on them."

At Seagold was an engineer named Bowie Keefer who had developed an energy recovery pump that could sustain 800 to 1,000 psi.

Seagold built the gadget, the Navy started testing it and now it's expected to be standard issue on as many as a thousand lifeboats by next year.

According to a report issued by the Navy, the desalinator "was operated on the open ocean by two Navy enlisted men for 7 1/2 hours. Each man alternately pumped the unit for up to 35 minutes each hour and produced better than one gallon per hour of drinking-quality water."

The world may yawn and offer a big "so what," but to seagoing dreamers like me the Navy's new gadget is as comforting as a fair wind on a calm sea.

Imagine! Make your own water! One fewer reason to ever have to stop at that most despised place of all, land. SALT-FREE The Navy figures the new desalinators will cost about $500 each, but that price presumably would drop significantly if mass production for private use developed.

Pizzino and Adamson said the current life of the unit is about 250 hours, after which the seal on the pump is likely to go. But they're shooting to improve it up to a 600-hour lifespan.

The Navy will save money and weight with the gadgets. Currently, life rafts pack 75 cup-and-a-quarter tins of drinking water, as well as five desalting kits, which use a silver solution to precipitate out the salts. Each desalting kit makes eight pints of water, but the cost of silver has skyrocketed so that the Navy needs a cheaper way out.

The hand-operated pump would cut weight by up to two-thirds, increase the amount of fresh water and cut those costs, according to Adamson.