p.1

New concept offers many choices.
A side from its technical distinctions, the so-called Grefco (ground effect vehicle) concept is distinguished by its acknowledgement of the marine industry's cost sensitivities.

p.2

p.3

The family of Grefco designs initially proposed 
encompasses 60m freight carriers, suited to ferry or supply ship roles, and a range of 135m vessels for unit load or ro-pax applications. 

p.4

The initiative has also entailed development of a powerful calculation and simulation design tool. 

The Grefco interests have retained sales, marketing and design company Conoship International, based in Groningen, as a contact point and intermediary. 

The move may be seen as part of the wider strategy to bring the Grefco concept to commercial reality through the creation of an operating company, eventually backed up by four production and assembly sites around the world.

p.5

Further drawbacks attributed to the previous generation of air-cushion craft have included a large energy requirement, high operating costs, and lateral wind effect and localised environmental disturbance.

The Grefco vessel operates completely out of the water, with only the propulsors immersed, and incorporates suspended skirts, affording significant freedom of movement relative to the hull. 

p.6

The air support system is divided into a minimum of four cushion chambers, with segregated air inputs. 

The skirt suspension and control system is based on pressure fields, restricting air leakage, and curbing the amount of power needed to maintain the air cushion.

The very low skirt and surface friction factors reduce propulsive power requirements for a given speed. 

The skirt provides support, in line with the designer's aim for craft robustness, along with stability and shock absorption. 

The suspension-like response to a disturbance reduces acceleration requirements and the associated power uptake, while enhancing onboard comfort. 

p.7

An active control system will dampen vertical motions, contributing both to passenger comfort and vehicle or freight security.

The greater stability factor has facilitated the use in the amphibious Grefco craft of a marine propeller or waterjet and ground propulsion in preference to an aerial propeller system, while reducing power needs. 

Immediate promotional efforts relate to a design standard of 58m structure length and 62m vessel length, including a vehicular ferry offering 330dwt and powered by two diesel engines producing a total 14,700kW. This gives a cruising speed of 50kt at less than 11,000kW output. 

p.8

The overall beam, inclusive of the cushions, would be 37m. A pure ro-ro freight carrier within the S56 family is the STT56-6, designed to transport 18 trailers of an average 20 tonnes apiece. 

The SCF56-6 has an operating weight of 690 tonnes, and an air cushion envelope of 37 x 56m. There is 6m clearance between the hull and supporting surface, and the natural frequency of the craft is 0.5Hz. 

In support of the favourable seakeeping properties claimed for the design, a preliminary study was conducted into the craft's response to various sea states, and at vessel speeds between 10 and 50kt.

p.9

Another of the early propositions is the SCF135-10, a 57kt ro-pax ferry of 144m structure length, 149m vessel length and 120m beam encompassing the air cushions. The model has been prepared in three passenger/truck/ bus/car configurations, at a common 4,000dwt, and with passenger capacities between 2,000 and 4,000. 

The 56- and 135-series designs provide the template for a number of other versions, including types offering a competitive deck load capacity for containers or unitised freight or re-supply materials and equipment. 

p.10

The Grefco concept's champions argue that the overall cost in its 62m ferry version, for instance, would amount to just $0.03 per dwt-km. This is comfortably below the $0.045 dwt-km for road freight transport and less than cost figures for other types of high-speed ferry and projected fast ships. Cost comparisons are said to favour the Grefco even more as vessel size increases, as economies of scale are brought to bear. 

The accent on low running costs and maintenance expenditure is complemented by design and manufacturing solutions aimed at ensuring competitive newbuild purchase costs. 

p.11

The S56 type would be well suited to just-in-time 
shipping and logistical requirements and to companies looking to ensure deliveries within 24 hours or a similarly demanding timeframe. 

The S135 series is also considered a potential candidate for high-speed freight transport on major long-distance routes. 

The business goal is to sell Grefco S56 and S135 designs into 500 of the potential 4,100 high-speed vessel newbuild projects forecast to come to fruition over the next 15 years. This would equate to 12% of the fast commercial vessel market.

p.12

In the follow-on stage, production sites and assembly units would be opened as required in commercially strategic locations, including Asia and North America.