Radio Controlled Boats: Pros and Cons of Jets

Jet boats are a growing area of radio controlled boats. They are appealing as no propeller means their boat can't get entangled in weeds or hit the ground, both of which will bring you to a shuddering halt. Jet boats clearly have some advantages but they are not a panacea and have their own failings.

PROS
There is no propeller to get entangled in weeds and line. The water supplies the power by sucking in water from under the boat into a pump-jet inside the boat, then expels it through a nozzle at the stern. There are no props to damage even if you run it up on shore so it allows operation in very shallow water. Steering is as simple as a rudder as a motor/servo moves the jet nozzle to either side. The jet is expelled above the water line as it is significantly more efficient and lets the boat go faster by avoiding drag. Jet powered boats are highly maneuverable, and many can be reversed and brought to a stop quickly

A very positive upside for many is that without most of the sharp external parts such as propellers the boat isles likely to cause damage by cutting people or wildlife. You can have high maneuverability for example because steering is still available in reverse, you can turn the boat on the spot once you reach a 'balance' point with forward and reverse thrust. Jet boats plane across the water ie the front of the boat lifts out of the water, this reduces drag, boosting speed and maneuverability.

CONS
A problem some people have is that jetboats don't track well like prop (propeller) driven boats. There is no rudder sticking down into the water to give the boat basic stability or to hold the boat's direction. When you execute a turn there is quite a bit of force that pushes you to the side (its like being in a car that takes a corner at speed). The sideways leverage comes from higher up on the transom (the surface that forms the stern of a vessel) just because of the way the jets are set up and while this means they don't heel (lean) over as far, this makes them much more liable to slide out on the turn a lot more. As with anything knowing that it happens allows you to correct for the effect but it takes practice (and plenty of room)

Given the boat relies on the flow of water through the nozzle for control, you must have the throttle open to steer it.
They quickly slow down as the hull comes down and hull resistance is increased. However, loss of steering control at low speeds can be reduced by lowering the reverse deflector slightly and increasing throttle - so you increase thrust and thus control without increasing boat speed itself. Again practice is key.

People who run jetboats may want to run them in shallow water, but this has its perils for jet boats too...even though there is no prop to hit, if you hit sand or pebbles the suction from the water pump will send sand, pebbles or rocks through the pump and this will start causing damage. Sand can damage the bearings, pebbles can damage the impellor. Some pumps come with intake grilles which are recommended. It's a risk to run without them but you do get more power.

At this point unless you are pretty advanced I would recommend prop driven electric, nitro or gas boats.

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