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Title: The Evolution of Small Waterjet Propulsion Systems within Recent Years

Authors: Jari Kuivanto and Hannu Rantala

Abstract: Over the last five years, a lot of work has been done to develop waterjets below 500kW into not only better performing, but also easier-to-install systems.

Regarding performance, significant improvement was achieved i.a. by enhancing cavitation resistance without the loss of top speed. This enables higher towing capabilities, better vessel acceleration and negotiation of the planing hump more easily also in laden condition.

Bearing boat designers in mind, an installation method allowing two different ways of placing the propulsion system into the hull was developed. The patented Combi-Frame structure makes it possible to install the same jet either long tail or short tail, meaning a longer or shorter protrusion respectively of the system over the transom. This creates more freedom for layout design, optimization of the center of gravity, and for maintenance aspects.

The end user has been considered by integrating more components into the waterjet than before, e.g. a steering cylinder, which normally is not a standard component on propulsion systems of this size. Maintenance procedures are substantially easier to perform due to the increased size of the inspection hatch. According to surveys, the location of this inspection hatch has always been subject to differing opinions among customers. The Combi-Frame structure provides a solution for this dispute, as the hatch can be located either inside or outside the hull, depending on the above mentioned installation method.