You Could Get Exercised Over Wee Sub : Inventions: After three decades building one-person and two-person crafts, former Navy captain is working to perfect a human-powered version.

George Kittredge built his first miniature submarine because he wanted to see the bottom of the ocean. Now he is developing what could be the “ultimate exercise machine.”

After three decades of building one-person and two-person subs that are powered by electrical batteries, the 76-year-old former Navy captain is working to perfect a human-powered craft.

Kittredge admits that more than one of his neighbors in the small coastal community where he lives halfway between Portland and Bar Harbor have asked why he would want to build a submarine that is pedaled like a bicycle.

“I (tell them) this is going to be the ultimate exercise machine,” he said with a laugh. “You get in, pedal yourself down to 250 feet, rest a bit, and then if you have the strength you pedal yourself back up.”

In the event the operator is too tired to pedal back to the surface, the submarine--which looks a bit like a fuel tank--has four redundant safety systems that allow the craft to rise on its own.

Kittredge has built 41 battery-powered miniature submarines since he retired from the Navy in the 1960s. He said the decision to build the first one was prompted by something he could not do in the military.

“When you’re in a military submarine you can look through the periscope but you can never see the bottom,” he said. “I decided that I wanted to see the bottom.”

Kittredge’s submarines provide plenty of opportunities for looking around while under the waves. There are four portholes at eye level, and a larger viewing window on the floor near the operator’s feet.

The operator controls the craft with handles connected to its rudders and ballast tanks. “Simplicity is the key to underwater work. You don’t want it to get complicated,” he said.

Kittredge’s new sub follows the same basic design as his battery-powered craft--a design, he proudly notes, that has been certified by marine engineering societies in the United States, Britain and Japan.

It was partly out of frustration that it took up to eight hours to charge the batteries in his conventional submarines that got Kittredge thinking about using human power.

Kittredge calculates that someone in good physical shape should be able to generate a half horsepower. “That ought to be able to move a vehicle along,” he said.

Kittredge admitted, however, there was a hitch during his first tests of the human-powered sub. He accidentally placed the gears in backward, an error that caused the propeller to rotate at a slower rate than the pedals.

“I had it in the water twice; it just didn’t move very fast,” he said.

Although Kittredge ended up rowing the sub back to shore, he said he still has “the greatest confidence” he will soon get it working the way he wants.

Kittredge has more time these days to work on the craft. He has signed a licensing agreement with a Japanese company that allows the firm to produce his battery-powered submarines.

The human-powered design may not be Kittredge’s last innovation of submarine technology. He is also developing a new underwater salvage business, although he is reluctant to talk about future plans.

“I don’t think that old men should tell what they intend to do in the future. It really bores people and people don’t believe it,” he said.