Low-pressure water-jet technology is finding increasing popularity with fish and oyster boats in North America due to its low maintenance requirements.
Typically, water jets are high-pressure (30-60psi) water pumps and the clearance between the impeller and the wear ring is critical to maintaining performance. If the clearance is increased by sand and other debris, performance can be reduced by 50 percent, says North American Marine Jet (NAMJ) sales and application manager Jason Hill. In contrast, the company's low-pressure Traktor Jets operate at a maximum pump pressure of 15psi. This allows NAMJ to design clearances ten times that of typical high-speed jets.
"The Traktor Jet can give the customers a lifetime of service without replacement or rebuild," says Hill. "Traktor Jet propulsion is engineered to have very low to zero cavitation range, which allows for better cruise rpm with less horsepower. It produces extremely high bollard pull, 50 to 70 percent that of high-speed jets with the same horsepower, and this allows the Traktor Jet to achieve planing in a craft laden with more weight that other propulsion systems."
The latest model jet, the TJ-610HT, is being installed on eight new vessels used for Alaska's Bristol Bay fishery. The vessels are ten metres long and five metres wide – fishery requirements set this maximum length but any width is permissible. NAMJ's Traktor Jet provides enough thrust to push the vessel, with a single John Deere engine and jet combination, at 27 knots unladen and at 12 knots carrying 9,000 kilograms of fish. Three oyster boats have also been built, and another two are under construction, with a similar single-jet configuration. One 20-metre oyster boat, built by Everest Marine and owned by Coast Seafoods Company, can achieve speeds of 21 knots.
A third vessel type where these systems show their value is the seine skiff. These vessels are used to pull the large nets off a seiner and around the fish. The skiff then comes back to the seiner and hands off the line while inside the net circle. As the seiner is pulling the net in, the skiff holds the seiner in position so the fish cannot escape. The skiffs therefore need high-bollard pull. They also need to be able to pull net along the beach and to run back and forth over the nets.
NAMJ has supplied Traktor Jets for seven skiff newbuilds and one repower. The 224kW TJ457HT Traktor Jet has a 457-millimetre, 11-blade impeller and can deliver 1.9 tonnes of bollard pull. It can push a seven-by-three-metre skiff weighing 4.1 tonnes at 30 knots.
NAMJ also produces an HH series designed to produce high thrust with higher head (pressure) for when fast boat speed is required. A TJ381HH system was retrofitted on another skiff to replace a high-speed water-jet. The TJ381HH has a 381-millimetre, seven-blade impeller, and in combination with a 227kW Cummins QSB engine, delivered a top speed of 30 knots and over 1.5 tonnes bollard pull to the skiff.
All Traktor Jets are axial flow units that operate at low shaft speeds (300-1,050rpm) and are suitable for diesel engines of up to 895kW. Their advantages include low maintenance, easy installation, quiet operation and no hull protrusions, making them ideal for shallow-water applications. They are suited to applications such as work-boats, oil recovery/boom boats, fishing seine skiffs and tenders.
For more information contact:
Wendy Laursen