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Jet Boat Basics
written by Jeff Knapp

If you're wanting to reach waters where fish are rarely disturbed by the casual fisherman, try a jet-powered boat to glide across inches-deep water.
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Jet Boat

Jet boats can go where many standard boats can't, opening up miles of undistrubed areas.

Shallow-draft boats driven by a jet stream of water can propel an angler to portions of free-flowing rivers that see a comparatively light fishing pressure. Standard propeller-driven boats are limited to deeper pools of such rivers. Jet-powered boats can glide across inches-deep shallow riffles, opening up miles of otherwise undisturbed areas.

Jet Unit

Though it's possible to purchase an outboard engine set up as a jet from some manufacturers, most outboards are converted by a local dealer. In the process a mechanic replaces the outboard's lower unit — the part that houses the gearbox, propeller and skeg — with the jet unit, which is essentially a water pump.

Major components housed within the jet unit include the water intake, impeller and nozzle. As its name suggests, the water intake draws in the water from beneath the boat's hull, directing it into the impeller. The impeller, driven by the outboard's driveshaft, spins the water into a high velocity flow. This flow is channeled through the unit's housing and discharged out the back as a high speed jet of water, the force of which pushes the boat. A deflector pivots into place when the operator shifts into reverse, which swaps the direction of the stream's flow allowing the boat to be backed up.

The jet's intake hangs 1 to 2 inches below the boat's hull, providing the clearance needed to glide across the shallows.

Boat Considerations

Though the outboard jet conversion is a relatively simple process, getting set up to run the shallows isn't as simple as high-tailing it to the local marina with your current boat to have the work done. To ensure optimal performance the boat's hull design is a vital aspect.

Jet Boat

A flat hull allows the jet outdboard to receive a smooth supply of water.

To work efficiently a jet outboard must be fed a smooth supply of water, something best accomplished with a fairly flat hull. Heavy duty all-welded aluminum jonboats with a slight "V" — 6 to 10 degrees dead rise is ideal — achieve this. The hull provides a solid air-free flow to the outboard — pushing bubbles out to the side — and has enough bite to keep the boat from skating sideways on turns and when hit with a strong crosswind. The small draft of a johnboat is also a benefit, as it allows an angler to float downriver through skinny water when fishing without bumping bottom.

Compared to a riveted boat, a welded hull is less likely to open up if you hit an obstacle while under power. Naturally, hull thickness plays into this as well. A thickness of .100 inch is a good balance of strength and weight, and is adequate on moderate gradient rivers where sand/gravel is the primary bottom composition. Rivers that are particularly nasty to navigate (i.e., expanses of bedrock bottom) often require thicker hulls, stronger aluminum alloys, and/or the addition of synthetic polymer bottoms.

The pilot's station is also an important consideration. Basically the choices are: side console, center console and tiller — each with advantages and disadvantages. Since the operator is standing, the center console provides the best vantage point for navigating the shallows. It also takes up the most room. The tiller takes up the least room, but affords the poorest view, since the pilot is sitting in the back of the boat. The operator also sits behind the side console, but is located farther forward. The side console eats up less floor space than a center console.

Motor Considerations

Though the word "jet" conjures up images of power, jet outboards generate about 30 percent less power than the same unit equipped with a propeller. That being the case, it's best to outfit your boat with the maximum horsepower outboard the boat is rated for.

In general, two-stroke outboards offer significant advantages as jets over four-strokes. They tend to be lighter and have more torque, though the gap between the two is closing. A lighter outboard helps balance the craft better, keeping it more even on the drift (when fishing), whereas a stern-heavy boat is more likely to bump.

The addition hole-shot torque provided by a two-stroke is a big deal, getting you out of the shallows before the jet starts sucking up gravel, weeds, etc. Also, two-strokes often have a lower profile, giving the angler in the back on the boat more room. A big plus of the four-stroke is the added fuel economy, something that helps offset the comparative inefficiency of a jet drive. And you don't have to feed a four-stroke expensive oil like you do with oil-injected two-strokes.

Navigation Considerations

Any attempt to describe how to run shallow rivers is beyond the scope of this article, perhaps any article, since this is a classic example of experience being the best teacher. The trick is gaining that experience without cracking a hull or smacking the jet's intake foot. The following tips should help you accomplish that.

Start off by taking things slow. Take your maiden voyage on deeper water, where you don't have to worry about hitting shallow obstructions. Get a feel for the boat. Jets handle differently than prop-driven boats, particularly at low RPMs. You'll miss the "bite" of the propeller, especially during your first attempts to drive the boat back on the trailer.

Once you've gotten accustomed to the boat's feel, it's time to begin learning to navigate shallow water. If at all possible, learn new water by navigating upriver. It's easier to read water when you're looking "uphill."

Jet Boat

The jet's intake hangs 1 to 2 inches below the boat's hull, providing the clearance needed to glide across the shallows.

Rivers have current and that current will reveal subsurface obstructions. Current flow over individual rocks will produce a boil. The boil will be downriver of the actual rock. Like a pothole in the road, you'll want to avoid running directly over the boil.

Riffles are formed when the slope of the river increases and the resulting faster flow encounters rocks. Bigger rocks, which are likely closer to the surface, tend to produce more "whitewater;" often the key to running these areas is in weaving between the bigger "waves." Every riffle area is different, though, and must be learned on an individual basis.

Often some of the shallowest spots in a river are immediately upriver of a riffle area. As a deep pool gradually tails-out before spilling into the riffle, conditions often get quite thin, especially if the river widens at that point. The shallowest water will often exhibit a ripple across the surface, caused by current flowing a mere couple of inches above gravel. Typically there's a "tongue" of slightly deeper water which shows itself as a "V," indicating the channel to take.

In hilly country there will often be a steep side to the valley, and a flatter "flood plain" side. The deeper channel is usually closer to the steeper side.

It's common when fishing a shallow river in a jet boat to drift downriver through potentially productive areas. If you can drift down through an area, you can run back up it, as the boat takes less water when on plane that it does when not under power.  In summer, when the water's typically at its lowest, be sure to wear some type of water shoe (or old sneakers) should you drift up on a rock or shoal. The same goes for your fishing buddy. Removing the passenger weight from the boat should allow it to float free, though you'll likely have to give it a boost.

Expect to have a few white-knuckle moments as you ride the river-running learning curve. The first couple times, when out of the corner of your eye you see shallow rocks whizzing by at 30 mph, you'll likely back off of plane, sink down and nudge a bottom you'd have otherwise missed. But soon you'll gain the confidence to shoot through these spots as you discover what your new fishing tool is capable of.

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