As part of the International Hydrofoil Society’s 50th Anniversary on-line conference during October and November, a team from Kawasaki Heavy Industries (KHI) discussed the recommencement of Jetfoil passenger hydrofoil ferry production after a pause of 25 years.
The team consisted of: Kentaro Kai, KHI Jetfoil Project Manager; Kenichi Kitabayashi, Manager of KHI’s High-Speed Ship Designing Section; Takeo Ui, Manager of KHI’s Machinery Planning Section of Engineering Division; and Toshiyuki Hotta, General Manager of the Engineering Division at KHI subsidiary KHI JPS.
The Jetfoil hydrofoil, featuring automatically controlled fully submerged foils and waterjet propulsion, was originally developed by Boeing Marine Systems in the 1970s with the first craft being launched in 1974. Boeing built a combined total of 28 craft of this particular model and of revised designs up to 1986.
After concluding a license agreement in 1987 to take over Jetfoil manufacturing and sales rights from Boeing, KHI built 15 further Jetfoil craft between 1989 and 1995.
The then-latest model was a further refinement of the earlier Jetfoil designs. The majority of the Kawasaki-built Jetfoils were for the Japanese market, though two examples were also originally delivered to a Spanish operator.
Since 1991, a KHI subsidiary company, KHI JPS, has continued to provide product support for the Jetfoil fleet, of which 21 are currently in service with seven operators on six domestic routes and one international route in Japan while a further 13 operate between Hong Kong and Macau.
Renewed local interest spurs restart of manufacture
In 2017, following a planning period which commenced in 2010 and following an order for a new Jetfoil from local operators Tokai Kisen and the Japan Railway Construction, Transport, and Technology Agency (JRTT), KHI commenced production of a new Jetfoil craft, the first such vessel to be built in Japan in over 25 years. The new craft, named Seven Island Yui, was launched at KHI’s Kobe Works in March 2020 and was delivered on June 30. It now serves a route between Tokyo and its surrounding islands alongside three other Jetfoils.
KHI Jetfoil project manager Mr Kentaro Kai and his colleagues provided an overview of current Jetfoil services in Japan before discussing the construction of Seven Island Yui. They indicated that the 21 Jetfoils currently in service in Japan carry approximately 200,000 passengers annually. With a foilborne speed of 43 knots and typical capacity of 250 passengers, they are able to maintain foilborne operations up to a significant wave height of 3.5 metres.
Video footage was shown of operation of one Jetfoil in approximately three metres significant wave height with little motion evident within the passenger cabin.
KHI sees the main attributes of the Jetfoil as being the comfort level it provides when operating in a seaway, the shorter transit time on the route, the ability to maintain high service availability even in rough seas, safety of navigation (i.e. a high degree of manoeuvrability and the shorter braking distance after making a full crash stop from high speed), and the low wave wake generated when operating foilborne.
Modernising the fleet
When considering future demand for new Jetfoils, Mr Kai indicated existing domestic operators had been surveyed to gain their views. Jetfoils were judged to remain an essential means of travel between the Japanese mainland and the surrounding islands with no equivalent replacement available aside from new Jetfoils.
The growing age of the existing fleet will make the need for replacement inevitable. The oldest operating Jetfoil is 42 years old, while the youngest, apart from Seven Island Yui, is already 25 years old.
In fielding questions, the KHI representatives advised that the specification for Seven Island Yui remains consistent with that of earlier Jetfoils built by the company given the operators are satisfied with the existing design. However, changes have been incorporated in the latest Jetfoil to account for obsolescence of various systems. For example, the former analog wheelhouse instrumentation has largely been replaced by computer screen displays, though the control layout still mimics the look of the earlier analog instrumentation to help ensure crew familiarity across the fleet.
The automatic control system for maintaining the dynamic stability of the craft when foilborne has also been replaced by a fully digital system. Newer and more impact-tolerant passenger seating has also been adopted.
As the Rolls Royce (formerly Allison) 501-KF gas turbines fitted to the existing Jetfoils are no longer in production, spare units available from the operator had been used for Seven Island Yui. For future Jetfoil production, an alternative supply chain of suitable lightweight propulsion units will be necessary.
The main areas requiring maintenance work on the Jetfoils were indicated to be the gas turbines and the foil units. The foils can experience impacts with debris and – on occasion – marine life. To that end, options for collision detection systems are being examined.
The waterjet pump housing has a lifespan of around five to six years. This discussion of housing erosion prompted John Kecsmar from Ad Hoc Marine Design to note that in his earlier experience with waterjet-powered catamarans, jet ducts constructed of GRP were far less prone to erosion damage compared to aluminum alloy, and so he offered this as a possible alternative material to consider.
However, supply of replacement housing units is currently readily available from KHI company KHI Marine Machinery and is thus not regarded as a significant adverse issue.
The Jetfoil’s operating cost per passenger was further stated by KHI to be approximately US$50 per hour.
The agreement between Boeing Marine Systems (BMS), a division of the Boeing Company, and KHI in 1987 licensed the Jetfoil design and the right to manufacture the vessel to KHI. Fortunately, it did not preclude Kawasaki from incorporating refinements to the design. Indeed, Harry Larsen, Business Planning Manager of BMS and the one who developed the specifications of the license agreement proposed to KHI as well as a participant in the session – emphasised that this agreement had expired many years ago and the license agreement itself had no restrictions on the vessel’s subsequent redesign by KHI.
Considerable further information about operation of the Jetfoil can be found at the Jetfoil Mini-Encyclopedia by KHI JPS here.
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