Ship & Boat International: eNews July/August 2020
Where does one go after monohulls, catamarans and trimarans? For vessel design consultancy BMT, the answer is the ‘Pentamaran’, a hullform developed for a proposed unmanned naval and patrol craft, capable of long-range operations and optimised for reduced fuel consumption.
The Pentamaran has been arranged to carry various payloads and sensors, explains Martin Bissuel, business sector lead for specialised ship design at BMT. He tells Ship & Boat International: “Alongside applications such as patrol and hydrographic missions, which would be manned or partially manned, the Pentamaran is designed for the latest military applications.” These could include anti-submarine warfare, sea-lane clearance support and aerial drone launch/recovery.
The initial Pentamaran design would feature a length of between 40-80m, to be scaled up or down depending on end user requirements. Two versions have been proposed, comprising 40m and 62m units. Bissuel says: “We have run models where the 40m vessel will be able to conduct 40-day deployments, while 60 days can be achieved with a 62m version.” To keep vessel weight down, the hull would be constructed in aluminium, though “for the smaller units, composites could also be considered,” he adds.
The design incorporates a narrow central hull, flanked by two smaller hulls on each side, for five hulls in total. “The two small hulls or sponsons are set one behind the other,” Bissuel explains. The chief benefit of this arrangement is minimised drag. He elaborates: “In calm conditions, the forward small hulls or sponsons on each side are not submerged in the water, and therefore do not generate any drag. These forward sponsons serve to supply roll stability when waves develop and, as a result, the Pentamaran has less hull volume permanently immersed in the sea than a trimaran would have, resulting in reduced resistance through the water.”
As an extra benefit, BMT predicts that the Pentamaran’s lateral accelerations will be far lower than those of a standard trimaran hullform, thereby reducing g-loadings on the vessel’s structure. In achieving low resistance in the water, the Pentamaran is expected to perform well at medium and low speeds.
With regards to the Pentamaran’s autonomous operations, Bissuel continues: “Removing the human operator requirements fundamentally changes the design philosophy…[this] impacts not just the configuration of the power systems, but the entire below-decks arrangement. The propulsion design could therefore move away from conventional set-ups.
“Multiple diesel-electric generators provide power for electric propulsors. The generators are positioned in different locations or compartments, thereby increasing survivability, but also resilience: if one of the generators has an issue, power can still be provided by the other units.” The use of smaller generators will also simplify maintenance procedures, he adds.
In an online Q&A session hosted in June, Steven Lee, BMT project manager and naval architect, added that the design house was proposing a set of three engines in one machinery space and three in another. For “normal loitering speeds”, Lee said, the Pentamaran would draw on one generator, meaning that “a single unit would be operating more efficiently compared to multiple diesel propulsion engines”. When transiting at its cruise speed, the boat would run on three of its six generators, switching to all six for high-speed operations.
