Knocking the props from under 'em

Dec. 18, 1972
Dec. 18, 1972

Table of Contents
Dec. 18, 1972

Blahs In Big D
Back Again
19th Hole: The Readers Take Over

Knocking the props from under 'em

By Hugh D. Whall

I push the first valve down, the music goes 'round and a-round...and it comes out here." Say water instead of music and you have a fair description of what happens in a fascinating new kind of boat—the hot, wet jet. This is not the jet that propels airplanes but a neat little device that sucks in water here, pumps it around a bit and then shoots it out there with enough wallop to pull a water skier or win a drag race.

This is an article from the Dec. 18, 1972 issue Original Layout

Two large manufacturers have recently added jet-powered boats to their lines, thus bringing them out of the experimental stage into public use. Outboard Marine Corporation has linked two of its marine engines to water pumps built by Jacuzzi. Chrysler is readying an all-Chrysler package for sale in early spring.

But why the jet? Why not stick with the jet's closest cousin, the inboard-out-drive? Well, say a sandbank surfaces ahead. Instead of swerving away as one would with a propeller-driven boat, with a jet the driver throws a single lever—and hangs on. What happens next is the sort of thing that occurs when an airplane touches down and the pilot turns on the reverse thrusters: the boat brakes. Instead of gear teeth and bits of engine churning into scrap, as would be the case if a conventional transmission were suddenly slammed from full ahead to full astern, a gate closes around the jet stream and the boat reverses.

Even if the jet boat hits the bank full tilt it probably will hurdle right over. There is no prop or shaft or skeg or rudder on the bottom to snag. Indeed, when the Buehler Corporation introduced its Turbocraft a few years ago, a favorite method of ballyhooing it was to run it up and down such woolly waters as the Salmon, the Rouge and the grumpy Colorado. It bounced over sandbanks like a flat stone skipped on a pond and survived rapids that would have mangled a propeller-driven craft. But Buehler's jet system clogged up, it swallowed gas by the pumpful at low speeds and it had a nasty habit of spinning out in its own length.

Modern jets are much improved. Inspection plates tell when it is time to declog, and inadvertent spins are prevented by small ventral fins that keep a boat on a straight course. Unhappily, gas consumption and spongy low-speed steering continue to be problems. Figures from OMC reveal the difference between a 307-cu.-in., 245-hp V-8 linked first to an outdrive unit with propeller, then to a jet. At 25 mph the outdrive burns 5.4 gallons per hour; the jet, 6.9.

Docking a jet is no easy thing. It is sort of like sweeping a golf ball into a manhole with a high-pressure hose. One points the jet nozzle with the steering wheel and then, with a prayer, jabs the throttle to wash the boat in the desired direction. Everything seems to happen a bit slower than usual, and not always with complete predictability.

But slow-speed disobedience is a small price to pay for safety. Because the jet uses no spinning, carving propeller, it makes an ideal water-ski tow boat. The driver need never dread accidentally running over a skier, and a jet will accelerate and climb up on a plane just about as fast as the prop boat.

In brief the jet is nothing more complicated than an engine coupled to a high-speed water pump, which flings a stream of water out through a stern nozzle at a velocity of up to 5,400 gallons per minute. But because of a sluggishness at low speeds, jets are not recommended for heavy-displacement-type hulls. They will be utilized mostly in smallish family runabouts. They will also be used in bass boats; fish seem to like the sound of a jet but flee before the hum of an approaching propeller.

OMC will produce a 140-hp model which, mated with a Jacuzzi pump, will make one of the smallest, most economical combinations in jet boating. Chrysler's entries run from a 318-cu.-in. engine through 340 cu. in. to a 440-cu.-in., 330-hp brute. All will be married to pumps built by Chrysler engineers. "We have what we call a lateral thruster which gives more maneuverability," says Chrysler's Doug Talbot. "It steers almost like a small rudder and lends not only maneuverability when docking but stability as well. Yet the thruster doesn't reduce the shallow-water advantages of the jet. At this stage we feel our jets are every bit as efficient as the in-board-outdrive."

But any prospect of jets replacing prop power the way they have in aircraft seems at this point remote. Boatmen are fundamentally conservative; even those who buy high-velocity rigs can't help feeling that a boat without a propeller is like a plane without wings. A good many are going to change their minds, though, when they discover how neatly the jets handle the shallows.