Innovative hullform confers important advantages on newbuild CTV

Built by Työvene Oy in Finland, the newbuild, MCS SWATH 3, has a small waterplane area twin hull (SWATH) hullform and is the first of a series of three units under construction for the company.

The design is a result of a close cooperation between the owner, shipyard and designer Ad Hoc Marine Designs, and draws on experience gained by MCS operating two similar designs and from feedback from crew operating the  vessels. It will be deployed in the North Sea offshore wind sector.

As previously highlighted by OWJ, the SWATH hullform has a number of advantages compared to a conventional design. The main advantages of a SWATH over a 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.

A SWATH is a twin-hulled vessel which concentrates a large proportion of its flotation volume in bulb-like hull sections 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.

A vessel’s 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, and the SWATH design reduces the waterplane area to a great extent by having only two foil-shaped struts intersecting the waterline. Particularly at slow speeds, compared to a conventional catamaran, a SWATH hull also offers a significant reduction in CO2 emission. 

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

The new vessel also benefits from a power take-in (PTI) on each drivetrain allowing for hybrid operation.