BMT says its innovative pentamaran vessel has reduced fuel consumption and emissions compared to other hull types and can make USV operations such as offshore surveys less expensive. Using an unmanned vessel already eliminates the cost of crewing.
The company claims that tests have proven that its hullform offers ‘significant improvements’ compared to conventional hullforms such as monohulls, catamarans and trimarans.
The vessel has a very slender central hull and two smaller hulls or ‘sponsons’ on either side. The sponsons are set one behind the other and when the vessel is operating on flat water, the forward sponsons are not submerged, as they provide roll stability effect in waves only. Compared to a trimaran there is less volume permanently immersed and therefore less resistance through the water.
BMT business sector lead for specialised ship design Martin Bissuel said, “Our team have carried out extensive work on this. The data gathered through extensive towing tank testing is very compelling.
“For applications where fuel economy matters, the pentamaran hullform is more efficient than conventional hullforms, which means that using the same engines and the same amount of fuel, it will go further than any other, making it an ideal candidate for autonomous applications.
“Looking at it from a distance it may resemble a trimaran but that is where the similarities end. The arrangement and careful positioning of the four sponsons makes all the difference. The forward sponsons stay above the water, and only come into action when the vessel rolls, so not only the drag is reduced, but the sea keeping characteristics are improved.
“Compared to a trimaran hullform, lateral accelerations are lower, reducing g-loadings on the structure as well as the antennae and sensors on deck. The wide deck offers a large working area. It can accommodate payloads or interface with other systems,” said Mr Bissuel.
“A key consideration, when a vessel is operating autonomously for long periods of time, is the reliability of the propulsion setup which is essential to sustained operational readiness. Our engineers have therefore integrated multiple independent power sources to increase reliability.”
“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,” Mr Bissuel explained. “These forward sponsons serve to supply roll stability when waves develop.
“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.
“Also, the positioning of the outer hulls, length-wise, is absolutely key to obtaining the best results. Through extensive tank testing we have been able to optimise the overall arrangement of the hulls for the best possible results.”
Mr Bissuel said that, when looking at autonomous operations, removing the human operator requirements into the design fundamentally changes the design philosophy that impacts not just the configuration of the power systems but also the entire below decks arrangement. The propulsion design could therefore move away from conventional setups.
He explained that multiple diesel-electric generators provide power for electric propulsors. The generators are positioned in different locations or compartments, thereby increasing survivability, but also resilience because if one of the generators has an issue, power can still be provided by the other units.
“Maintenance is made easier, because of the smaller generators, but more importantly, operationally it provides what we describe as graceful degradation of performance if units should fail but providing high confidence that the unit can be returned,” Mr Bissuel explained.
“When it comes to endurance, the pentamaran has been designed to push the boundaries. The profile varies depending on the customer requirements. We have run models when the 40-m vessel will be able to do 40 days deployments, whilst 60 days can be achieved with the 62-m version.”
Mr Bissuel said there are a very wide range of missions the pentamaran could be used for, including launching and recovering unmanned air vehicles. It is designed to be a modular platform so that it can carry a range of payloads. The aft deck is very wide and provides a large amount of space. It can also be a platform for unmanned other unmanned surface and underwater vehicles.
“The pentamaran lends itself very well to high speeds because of its characteristics, but also performs very well at medium and low speeds because of its low resistance in the water. As for the hull construction, we have used aluminium to keep the weight down and therefore increase efficiencies, in line with the overall concept. For the smaller units, composites could also be considered.”
BMT’s pentamaran USV may be new, but the company has long recognised the potential advantages of hullforms of this type and over many years has developed a range of craft exploiting its potential advantages.
These include designs for yachts, high-speed ferries, and a novel fast pentamaran frigate design developed BMT Defence Services Ltd and BMT-owned design house Nigel Gee and Associates which was intended to meet a notional requirement for the UK Royal Navy’s post-2015 Future Surface Combatant programme.