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What is a JetPac?
A JetPac is a patented marine propulsion system that uses an automotive engine to power a large diameter waterjet, located directly below the engine, with a drive belt. The engine and water jet are both enclosed in a fiberglass shell, designed with enough buoyancy to fully support the weight of the complete unit, that attaches to the transom of a boat, like an outboard. To see how one is put together see the page "So what is a JetPac?"
What fuel does the JetPac use?
JetPac's can use either diesel or gasoline engines. The initial model is a 150 horsepower diesel.
What engines does the JetPac use?
The initial model features a 2.8 liter International Engines diesel.
Are there advantages of using diesel engines?
How does the JetPac mount to my boat?
The JetPac bolts to the transom of your boat much like an outboard engine.
Does the transom need to be reinforced?
No. There is no need to reinforce the transom of most production boats. The buoyancy of the fiberglass shell supports the weight of the engine when in the water, and the mounting hardware distributes the weight sufficiently when trailering.
How big is the waterjet?
The initial model uses a 250mm jet. There are plans for both larger and smaller versions.
Why are conventional inboard waterjets so expensive?
In a conventional waterjet installation, a boat builder has to install a marine engine, a marine gear and a waterjet unit inside the hull. Additionally, the hull has to be modified to incorporate the water intake for the jet.
Why do conventional inboard waterjets perform so poorly?
First, the question needs to be rephrased as "Why do conventional inboard waterjets perform so poorly on boats less than 30 feet?". Larger boats with jets perform admirably. In fact the number of commercial fast ferries using waterjets has increased dramatically.
So why don't smaller boats with conventional waterjets perform as well? The problem lies in three main areas.
The weight of the engine is too far forward. In a small boat with a planning hull, the weight of the engine needs to be as far aft as possible.
The water intake, cut into the bottom of the boat, reduces the planning surface.
Most conventional waterjets on small boats are driven at engine speed. This requires using a small diameter jet which results in less than optimum efficiency. A larger diameter jet could be used in combination with a transmission to reduce the speed of the jet; however, this would add more weight and move the engine even further forward.
What makes the JetPac perform better than a conventional waterjet?
The patented design of the JetPac moves the weight of the engine behind the transom, significantly further back than a conventional waterjet. The waterjet is mounted directly under the engine, and very close to the water intake, which allows for a much smaller water intake, which is part of the JetPac, not cut into the planning surface of the boat. Finally, the JetPac uses a large diameter waterjet and a gear ratio between the flywheel gear and the impeller gear which is designed specifically to give optimum performance.
How does the JetPac performance compare to a conventional propeller driven boat?
A properly sized JetPac will deliver significantly more static thrust and will perform comparably to an outboard at speeds from 20 to 50 knots.
How does the JetPac handle at low speeds?
Excellent! The JetPac outlet is 36 inches behind the boats transom. This gives much more steering stability than conventional waterjets with rapid high speed turns, superior low speed handling and excellent steering stability under full acceleration. Further, the JetPac does not have the torquing effect found on most propeller driven boats.
How does the JetPac handle in rough seas?
Excellent! The weight of the engine and the waterjet behind the transom combine to keep the water inlet in the water, even in very rough seas. Should the water inlet lose contact with the water, the impeller of the waterjet will cavitate momentarily until the water inlet comes back in contact with the water. Also, the air inlet into the engine compartment is designed to allow air in and drain water out through a baffled system.
How will using a JetPac affect my boats draft?
A JetPac draws significantly less water than other conventional systems due to the systems self-buoyancy and that no part of the JetPac extends below the keel of the boat.
What is the lifespan of a JetPac compared to an outboard?
Conventional outboards are made of aluminum and are raw water cooled. Aluminum and hot seawater are a poor choice for longevity. Couple this with extreme mechanical and electrical complexity in close proximity to the sea and the present longevity and reliability of outboards becomes miraculous.
The JetPac is made with a marine grade stainless steel waterjet and has a closed fresh-water cooling system all mounted into a fiberglass shell sealed against the elements. Further, the JetPac comes delivered with an engine and a properly sized waterjet, with the correct gear ratio, which results in a system that can't be overloaded. The waterjet puts the engine under a constant load which greatly extends engine life.
What are the maintenance intervals?
Scheduled maintenance intervals for the JetPac will be at least double that of an outboard.
How easy is maintenance on a JetPac?
The fiberglass shell is designed to give sufficient working room to accomplish routine engine maintenance. Also, both the engine and waterjet are easily removed from the fiberglass shell.
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