Ad Hoc Marine Design provides more details on advantages of MCS CTVs

A SWATH ship is a twin-hulled vessel which concentrates a large proportion of its floatation volume into bulb-like hull sections deep beneath the waterline. These torpedo, or submarine-shaped flotation bulbs support the vessel through narrow, hydrodynamically efficient hull struts and, in the case of the AHMD design, have additional motion stabilisation with zero speed heave mode controllable fins.

The vessel’s engines, fuel and other heavy equipment are contained within the upper haunch region for easy access and maintenance from the main deck, allowing the struts to only require minimal wiring and plumbing to pass through them, thus enabling them to be made very narrow and hydrodynamically efficient.

The main advantages of a SWATH hullform over a more traditional monohull or catamaran are the efficiencies derived from a low waterplane area and reduced vertical accelerations in rough seas, which allow for a wider window of operation with more comfort for passengers and crew.

“The waterplane area is a major contributor to wave-making drag and hence a vessel’s overall drag, as well as the vessel’s natural period of motion,” said AHMD. “A SWATH vessel design reduces the waterplane area to a great extent by having only the two foil-shaped, knife-like support struts intersecting the waterline.

“Particularly at slow speeds, a correctly designed SWATH hull offers significant CO2 reductions over a comparable catamaran or monohull. At much higher speeds monohulls and catamarans are able to utilise their hull shape to minimise resistance, whereas the efficiency advantages of the SWATH hull form begin to reduce with increasing speed.”

The reduced waterplane area also provides the improved seakeeping of a SWATH hull. “A vessel’s volume distribution and waterplane area are what causes it to heave and pitch as it passes through waves,” said AHMD.

“Reduce the waterplane area and this reduces the heaving and pitching forces that waves can exert on the vessel. Adding motion-control fins to the SWATH hulls as in this design reduces these vertical accelerations even further, making for a supremely sea-kindly ride, at any speed and sea state.”

AHMD naval architect John Kecsmar said, “For more niche designs such as SWATH hulls, there is nowhere near as much prior experience as there is for more conventional hullforms.

“Ad Hoc Marine Designs has been involved in successful, proven SWATH designs for more than 30 years. These range from 13 m in size up to service operation vessels designs of 71 m.

“Our back catalogue of successful SWATH designs spans from our first SWATH, Patria in the late 1980s – still the world’s fastest SWATH – and naval architecture design for the Lockheed Martin SLICE SWATH, through to our latest Typhoon-class CTVs.”

An extension of the existing Typhoon-class SWATH CTVs, the new vessels are fully IMO Tier III-compliant designs that offer an IMO specification ballast water management system and are ‘hybrid’ ready. The new design is a larger version of the Typhoon-class currently operated by MCS, pushing the safe operational envelope from their existing Hs of 2.5 m higher, to Hs 3.0 m.

The vessels will carry 30 tonnes of deadweight along with 24 technicians in comfortable business class seating with a low risk of seasickness thanks to the extremely low motions of a SWATH hullform.

MCS commercial director Menno Kuyt said, “The major advantage of the SWATH design is its superior response to high seas, allowing operation up to an extra 100 days a year over a conventional catamaran.

“In addition, the hullform exhibits extremely low resistance at low speed. This current SWATH hullform requires less than 50% of the power required by an equivalent size and displacement conventional vessel when operating at slow speed, reducing fuel consumption and CO2 emissions.”

Three vessels with the AHMD SWATH hullform are being built for MCS at Työvene shipyard in Finland.