Wooldridge Jet Boat
Have you ever been fishing in the braided Rakaia, Rangitata, or Waitaki Rivers and watched as a prop-driven boat has passed you by and wondered how he has avoided prop damage on the stones? Well, chances are the craft is being pushed along, not by a propeller, but by an outboard jet unit.
Southbridge Engineering has had over ten years experience in the field of outboard jet units. From importing the jet units from the United States to building up fully finished Divemaster and Wooldridge Boats. Southbridge Engineering also builds aluminium grain bins, alloy dump truck bodies, spray booms, and a host of other farm equipment, and so has a wealth of knowledge on all aspects of aluminium fabrication.
The Wooldridge is a tried and tested jet boat design from Alaska. The bottom of the aluminium tunnel hull is imported pre-folded from America, and the completely finished boat, ready to run, is built up at the Southbridge factory.
The key to good jet boat design, according to Lindsay Montgomery, the factory owner, rests with the shape of the hull, and the extended transom. For overall efficiency, fuel economy, and ability to get up on the plane, hull shape is crucial. Without this, you are a displacement hull boat instead!
The Wooldridge, being built from aluminium, is considerably lighter than a traditional fibreglass jet boat. This makes it much easier for one person to operate. The big east coast salmon rivers are tidal in their lower reaches and it is all too easy to be left high and dry by a receding tide. In this situation, the Wooldridge comes into its own, and can be dragged across the stones and back into the water by one person without “busting the boiler!” The aluminium hull, deck, and cockpit also offer the advantage of being more resistant to scratches and scrapes. Recent years have seen a huge increase in the popularity of aluminium boats, particularly for fishing, for just these reasons.
The left-hand side of the windshield swings forward to permit access to the forward hatch/foredeck. Loads of space here for a substantial fast-water anchor should you require it. Plus you can clamber on and off over the foredeck and keep your feet dry!
The power plant is a 90 horse power Evinrude V4 outboard coupled to an outboard jet propulsion unit. In all respects, the Evinrude is a stock standard item. In fact it would take only 30 minutes to convert it back to a propeller driven unit!
The V4 Evinrude 90 gets the Wooldridge up on the plane no trouble at all. Even with a full crew on board and heaps of fishing gear, the alloy Wooldridge gives away nothing in performance alongside a more conventional inboard jet unit.
The outboard jet units themselves cost around NZ$3,000-$4,000 and are imported by Southbridge Engineering directly from the United States of America. The jet units are also factory items and are factory made for each model of outboard motor, as opposed to being fitted with any sort of adaptor plate arrangement. Woolridge Jetboats website.
Outboard jet units are built to fit a wide range of outboards built by Suzuki, Honda, and Evinrude/Johnson. These factory jet units are available for motors ranging between 25 and 235 horse power.
The question is often asked as to whether the outboard jet unit, which is essentially a water pump, is less efficient than a propeller. The answer is yes it is slightly less efficient. All things being equal, you would need a 30 hp outboard and jet unit, to achieve roughly the same speed as you would from a conventional 25 hp outboard and propeller.
However, when you compare the outboard motor and jet unit configuration with a more conventional inboard jet boat there is nothing between them performance wise!
Further more the outboard jet arrangement has several advantages over a traditional inboard jet boat.
• It is much lighter, both for maneuvering in the riverbed and when towing.
• It is generally more economical to run than a big thirsty standard in board jet boat.
• It is much less expensive to purchase than an inboard jetboat. This is an important consideration if you intend to use your boat only for salmon fishing. For six months of the year it may get little use, and so it is harder to justify the expense!
• Outboard motors are safer than inboards in the case of fire. Outboard jet units can be tilted clear of the water to check the inlet screen for any debris without having to get under the boat. It is also possible to tilt the outboard jet in order to make any fine adjustments to improve the riding attitude of the boat in the water.
The outboard jet units are steered by turning the motor, and so the nozzle, from side to side as you would a propeller. For reverse a deflection bucket lifts up over the nozzle.
The jet units themselves are simplicity itself. As the turbine wears it can be moved forwards along its shaft to take up any slack inside the housing. This is achieved by the use of packing washers. It is also possible for a worn unit to be re-machined and reconditioned.
The approximate all up cost of the Wooldridge including boat, 90 horse power Evinrude V4, and factory galvanized trailer, all ready to go fishing is just NZ$27,000.