To design a passenger ferry which can go fast in shallow water, with minimal fuel consumption and with a very different usage in summer and winter. That’s a challenge every naval architect likes to take up. Following a presentation on LNG propulsion at a conference, Conoship got in contact with Wyker Dampfschiffs-Reederei (WDR), who were contemplating a tender for a new ferry at the time.

Full-custom and efficient passenger catamaran for German Wadden Sea

WDR has a long tradition of passenger services on the Wadden Sea, and it proved a good match with Conoship, where Managing Director Geert Dokter has worked for Wagenborg’s Passenger services for several years in the past. A team of four naval architects travelled to the island of Föhr in Northern Germany, sailed on one of the ferries and had an extensive discussion with the ship owner about their exact needs and challenges to overcome. A key part of the discussions were the applicable regulations. There is a German set of rules for the Wadden Sea, but also a new EU directive 2009/45/EC for intra-national shipping which overrules the national flag state regulations. Being a sea-going vessel in national waters, the Wadden ferry does not fall under IMO regulations for international shipping, but under the EU directive. With a top speed below 20 knots, it would also not be considered a high speed craft. To make matters complicated, the vessel does fall under the high-speed (HSC) rules of its classification society Bureau Veritas, but this is related mostly to structural strength and not to statutory issues such as lifesaving appliances.

Conoship was enthusiastic about the project and invested a significant amount of time in the pre-contract phase to get to the bottom of the regulatory issues and to work on the concept. One of the results of this was that they found out an aluminium vessel would be allowed – in spite of what was assumed at the outset in Germany. Aluminium with adequate fire insulation was significantly lighter, and also acceptable. Another key point was the embarkation and disembarkation of the Adler Rüm Hart.

Principal Particulars

Builder: Thecla Bodewes Shipyards

Owner: Wyker Dampfschiffs-Reederei Föhr-Amrum

Length oa: 34.40 m

Beam oa: 10.80 m

Depth: 3.00 m

Draft: 1.50 m

Main engines 2 x Volvo D16MH 478 kW at 1.800 rpm

Gearboxes 2 x Twin Disc MGX-5204SC 2,92:1

Auxiliary generators 2 x Hatz 4M41 28 kW

Bow thruster 2 x 26 kW

Max speed (at 85% MCR) 18 kn


Crew 3

Passengers (winter) 162 persons

Passengers (summer) 250 persons

Fuel tanks 6.00 m3

Fresh water tank 0.60 m3

Sewage tank 0.60 m3

Dirty oil tanks 0.33 m3

Guus van der Bles, naval architect at Conoship: “The tide difference is fairly large at each berthing location. Ferries with vehicles moor onto linkspans, which include a bridge which is lowered onto the deck, forming a ramp for the vehicles. The pure passenger ferries had a different berthing location, with passengers disembarking from the side onto a stair with landings at several heights. Because of the tides, these stairs are prone to algae growth, and therefore slippery, and the stairs made it impossible for wheelchairs and ‘walkers’. It is to be noted that a considerable amount of the day tourists, which typically use the fast passenger ferries rather than the roro vessels, are above the retirement age. Conoship proposed an altogether different solution: why not disembark from the front onto the roro- ramp instead of from the side onto the slippery stairs? When the solution was given a green light by the owner of the linkspans, it soon became a given in the project. This will make it much easier for passengers with reduced mobility to board the vessel.” Embarking on the port- or starboard side decks and the sundeck is also possible.

For WDR, the refreshing clean slate approach was such that for the first time in decades, they considered having their ship designed and built outside of Germany, where the consulted shipyards were proposing an update of tried and tested solutions, rather than something completely new. Because they initially intended to sail the vessel with a crew of only two persons, the propulsion power was desired to be maximized at 750 kW. With a service speed – over ground – of 16 knots, equal to the speed limit in the area, the vessel needed to have a service speed of 18 knots, so they could maintain 16 knots over ground in a head current of two knots. Achieving this speed with a passenger capacity of 250 people proved quite a challenge.

Conoship considered both a monohull and a catamaran, and in the end settled on the catamaran hull form because of its good properties in shallow water, being less susceptible to the so-called squatting effect. Squat happens when the water between the hull and seabed is accelerated due to the narrow passage. This venturi-effect causes a low pressure on the aft ship, leading to excessive bow-up trim and a sudden surge in resistance. Even before being awarded the design contract, Conoship worked with Van Oossanen Fluid Dynamics to optimize the hull form. In the end, the 750 kW target was relinquished, as a crew of three would anyway be needed for mooring operations and to provide assistance to the passengers, but setting the bar so high – or should we say low – really helped to obtain the most efficient hull form possible. Finally, at the speed trial the catamaran reached a top speed over 18 kn and at 18 kn the required power proved to be below 750 kW.

Redmer van der Meer, naval architect at Conoship: “CFD analyses were carried out to optimize the required power in deep water. The optimization resulted in two symmetrical hulls, with a very sharp bow, round-bilge midship sections and an aft ship with a relatively deep propeller tunnel in each hull, with minimal transom immersion. With a request for towing tank tests, the vessel was also tested at shallow waters. The hull was model tested at the towing tank in Vienna and scored exceptionally well for efficiency in shallow water. In shallow water a clearly different wave profile and resistance values were found, with the ship eventually sailing faster even on shallow waters”

The naval architects went beyond their pure engineering scope of work, and proposed the client to work with Sikko Valk from SiGu Design, an industrial designer who did his TU Delft graduation internship at Conoship, back in 2009. Sikko drew up a number of profiles and layouts, focusing on a balanced design with pure lines and characteristic details resulting in a fresh, modern appearance.

Finally, a builder was sought which would be capable of building the vessel in a short timeframe, as the goal was to be operational before the summer season of 2019. In addition to the strict time schedule, the yard had to run a tight ship on weight control. Thecla Bodewes Shipyards from Harlingen quoted and received the contract in January 2018. Elle Blauw, Managing Director of Thecla Bodewes Shipyards Harlingen: “We don’t have aluminium building capability in-house, so we subcontracted this part to Bloemsma from Makkum, and then transported the hull to our shipyard in Harlingen for outfitting on a barge. It was lifted with our Synchrolift and carted inside our production hall for outfitting. Because of the strict speed requirement, weight control was of the essence, and we used extremely light panels for floors, ceilings and walls. In spite of this, the vessel is extremely silent because of its low power requirement. At 18 knots, the noise level in the passenger compartment is only 61 to 66 dB(A).” The manoeuvrability of Adler Rüm Hart is excellent, with a tunnel thruster in each hull, and with the propellers so far apart, each with an independently controllable rudder behind it. To minimize the noise going outward to the Wadden Sea, the exhaust outlets are placed on the inboard side of each hull.

Thecla Bodewes: “Every Wednesday, Mr. Tholund of the ship owner visited our shipyard for meetings and inspections. The collaboration was very pleasant, and the client is extremely pleased with the result. We have to thank also our subcontractors, who made every effort to deliver to such a strict deadline.” During the five months in Harlingen, the complete mechanical and electrical installation took place, as well as interior outfitting and painting. The main electrical contractor was Alewijnse, with Radio Holland supplying the navigation and communication equipment. The heating, ventilation and air conditioning installation was done by Heinen & Hopman.

The vessel has a very different usage in summer and winter. In winter, transits are with only 20 to 30 passengers, a bit slower and much less frequently. The fuel tanks are dimensioned to allow for bunkering stops only every two weeks during winter operations. During the summer time, the upper deck (open-air) is also in use and the vessel can be fully booked with 250 passengers. The vessel is sailing almost continuously, and it is then acceptable to refuel every other day. Therefore, the ship carries much less fuel in the summer than in the winter, sailing at approximately the same load line.

Throughout the passenger compartment, the seating is arranged on rails, providing a high level of flexibility. As passengers enter, they can immediately leave their luggage in a storage space at the front. The wooden textures, warm colour scheme and ample windows provide a pleasant space, giving excellent views of the beautiful surroundings. A small bistro/bar serves drinks and snacks during trips. On the aft of the sundeck, a Marine Evacuation System is installed to provide a quick and safe means to evacuate the ship in case of an emergency.

In early May 2019, sea trials were conducted in both deep and shallow water, and the Adler Rüm Hart performed exactly as expected. The vessel then sailed to Wyk, where she was christened on 15 May. The vessel will be chartered by Adler Schiffe GmbH & Co, linking the Islands of Föhr and Amrum, as well as the Halligen of Hooge and Langeness and the mainland port of Dagebüll. In addition to commuter passenger services, the vessel will be used as a day excursion boat performing tours on the Wadden Sea lasting one to three hours.

For Conoship, Adler Rüm Hart is a project which shows exactly what they are capable of: thinking along with the client to provide the best solution, highly optimized in every respect for their specific needs. For Thecla Bodewes Shipyards, the vessel marks another successful reference in the growing market of passenger vessels, in an internationally competitive area.

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