Sendo Shipping is an inland container liner service operating routes between the North of the Netherlands and the Port of Rotterdam. Founded by three young entrepreneurs, brothers Sebastiaan and Dominic van der Meer and brother-in-law Edwin Groen, the company leans on the experience of several families with a strong heritage in inland shipping. The ships sail in a contractually fixed liner service for MCS Drachten BV, mainly transporting foodstuffs from the Groningen province to the Port of Rotterdam.

32 per cent less fuel
8 per cent more cargo

With several smart ideas, the owners have managed to both increase the payload – both for fully loaded containers and empty containers – while reducing the fuel consumption of the Sendo Liner. This was done by focusing on this goal from the first sketches and by starting with a clean slate.

The fuel consumption of the vessel was first reduced by optimizing the hull shape. Several variants were calculated in Computational Fluid Dynamics (CFD) by SIP Marine, who also supplied the propellers. The biggest gain was achieved by optimizing the aft ship more particularly for the sailing conditions normally encountered. While before, a ship would be optimized for the maximum speed (18 km/h) in deep water (trial condition), Sendo Liner was optimized for their most common operating condition: shallow water of just 1.5 metres below the keel and an operating speed of 14 km/h. This condition was chosen based on long-term full-scale measurements on another vessel in the Sendo fleet, called Nadorias. This measurement campaign was carried out by research institute MARIN before this vessel was converted to a hybrid propulsion installation, During the conversion, it became apparent that 20 per cent of the investment was spent on moving equipment which was already there, an expense which would not be needed in the case of a newbuilding.

As a starting point, Sendo Shipping asked SIP Marine to carry out a CFD analysis and power prediction for the Nadorias in the design condition for the new vessel. Dominic: “This analysis gave us two important take-aways: First of all, we knew that the performance prediction was accurate for our existing vessel in the conditions we operate in. Second of all, we now had a good benchmark against which we could compare the new design”. While they had expected a single-propeller solution the be the most optimal, it was actually the twin-screw version which showed the lowest power requirement. A lot of attention was paid to the shape of the tunnels, which are there to keep the propellers from sucking air in light-loaded or ballast condition. A different-than-usual geometry, well aligned with the flow (rather than drawing in water) and tapering down towards the aft, ensured that the water would almost not cross over the tips of the tunnels, leading to less vortices and less drag.

The aft ship was optimised for shallow water using Computational Fluid Dynamics

Principal Particulars

Hull Builder: Concordia Damen

Owner Sendo Shipping, the Netherlands

Length o.a. 110.00 m

Beam mld. 11.40 m

Depth 4.25 m

Draft 3.65 m

Main generators 2 x Volvo Penta 400 kW

Battery bank 500 kWh

Propulsion motors 2 x 350 kW

Max speed 21 km/h

Crew 5

Cargo hold 164 TEU

Fuel tanks 30 m3

Fresh water tanks 12 m3

Ballast water tanks 1,200 m3

Ballast tank in cargo hold 400 m3

Sewage tanks 2,5 m3

Luboil tanks 3 m3

At the end, the optimization yielded a reduction in required power of 32 per cent compared to the benchmark vessel, an investment which will be paid back easily during the construction (less power installed) and the lifetime (less fuel consumption) of the vessel. It is also plainly obvious that by reducing the resistance, and therefore the power demand, a future energy transition will be much more affordable.

In terms of carrying capacity of containers, two major steps were made. By reducing the length of the accommodation (and increasing its width), the length of the cargo-hold could be increased. This gave the possibility to store an additional row of containers forward, increasing the normal number of 13 twenty-foot containers to 14. Increasing the container capacity reduced the energy consumption per cargo unit by a further 8 per cent. The hydrodynamic shape of the hull required so-called ‘dummy containers’ on port and starboard side forward, but even this space was put to good use. One of the dummies houses one of the two 400 kW generators, while the other houses free space for future energy sources like hydrogen. The second generator is located in the space forward of the cargo hold. Having each generator in a separate compartment, and with the cables running completely separate on port and starboard side, the propulsion configuration has excellent redundancy. Furthermore, having all engines in the bow, resulted in an extremely quiet accommodation.

The battery room is in the transom

Propulsion is with two conventional shaftlines, each driven by an E-motor

The second step to increase container capacity was achieved by ballasting. On previous vessels, the number of full containers which can be carried was significantly larger than the number of empty containers, because of the limit in air draught. This resulted in an imbalance in container count, requiring additional trips to move empty containers from Rotterdam to Groningen. By increasing the ballast capacity, the difference between full and empty containers is reduced to only 8 TEU units. With partial bulkheads, a watertight compartment has been created in the middle of the hold (row 7 and 8). When sailing with empty containers, the lower part of this compartment can be filled with ballast water, and an ingenious system of tilting container supports allows the loading of containers on top of this. There are of course also built-in ballast tanks, and each of these is served by a ring-line with pneumatically operated valves. Sendo Liner can sail under an air draught of 6.7 metres with two layers of high-cube containers (which are increasingly common) and one layer of normal containers.

The main goals of this new design were to make the ship as profitable as possible and to make it futureproof for an easy transition to emission-free sailing. The latter has been achieved by using a modular diesel-electric propulsion installation. While powered predominantly by diesel generators in the bow, there is also a significant battery bank, located in the aft peak, with a capacity of 564 kWh (the equivalent of five top-of-the-line Tesla Model S 100D’s). These Lithium-Ion batteries were supplied by EST Floattech. They can be charged both by the onboard generators and by shore power during loading & unloading. The capacity is sufficient to sail for two to three hours with zero emissions, or to cover an entire day at standstill without any generator running. Because of this configuration, Sendo Liner does not need a harbor generator.

The battery capacity is sufficient to sail emission-free for two to three hours

Diesel generators are located forward, far from the accommodation

Compact jet bow thruster

Oechies Elektrotechniek took care of the entire electrical installation onboard, with their sister company Hybrid Ship Propulsion in charge of the propulsion system. This includes two Oswald permanent-magnet motors (AC) driving the conventional shaftlines. The variable frequency drives for the propulsion motors are located in the aft engine room and are watercooled. Each propeller is in a nozzle and followed by a pair of Easyflow rudders from De Waal (Werkendam), who also supplied the propeller shafts, shaft seals and the steering gear with a HybridTouch control panel on the wheelhouse.

The rudders are characterized by a slenderer profile and a position more off-center from the shaft, leading to a lower resistance. As a unique touch – only visible during drydockings – the rudders are painted in the bright green colour of Sendo Shipping. In the bow, there are two Veth Compact Jets as bow thrusters, each driven by an E-motor mounted vertically on top. These can deliver thrust in 360 degree and ensure excellent maneuverability.

Hybrid propulsion has many definitions. In shipbuilding, the term hybrid is often used to indicate that the propellers can be driven both in diesel-direct and diesel-electric mode, for example through an e-motor on the drive shaft(s). In automotive technology, the term hybrid usually means that there are batteries involved, allowing the wheels to be propelled either by an internal combustion engine or by battery power. Sendo Liner is what in car terms would be called a ‘series plug-in hybrid’, with ‘series’ meaning that propulsion is always through the electric motors, as opposed to a parallel hybrid, which would include a diesel-direct drive mode. ‘Plug-in’ means that the batteries can be charged by shore power, and not only by the onboard power units. The ratio between energy stored in batteries and energy stored in diesel fuel is something which may change in the future, depending on how the technologies and their price differential evolves. The ship is ready to go either way. While being the main source of power today, the gensets and diesel fuel may become merely a “range extender” in the future. All the electrical equipment, including the batteries, was delivered by Holland Ship Electric.

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The hull was built in Orsova (Romania), and is characterized by the fact that there is a double hull over the entire length of the ship, including the engine rooms. This increases the level of safety. The main contractor is Concordia Damen. They hired CCM3 (Werkendam) to do the mechanical installation of the vessel, which took place at Concordia Damen’s outfitting quay in Werkendam. Sendo Liner is equipped with two spud poles, which allow for mooring by pushing a button, thereby reducing the workload for the crew and the maneuvering time. The system is used at locks and during cargo operations in the North. The water is too deep in Rotterdam to use the spud poles. Each spud pole is operated by an electrical winch which is coupled to an echosounder, therefore preventing slack in the line or loss of grip when the water level raises. A tidal block in the lowest spud pole segment also provides some range of motion. Anchors are still provided in the bow as required by the regulations, but it would be worthwhile to re-evaluate the necessity of these regulations, as there is both a weight penalty from the anchors and a hydrodynamic penalty from the resistance of the anchor pockets.

The accommodation is full-beam, which means that you have to go over the accommodation to go from the main deck to the aft mooring deck. The result is that the interior is very spacious, in spite of the fact that the accommodation takes up less ship length. There are spacious cabin for all the crew – allowing for a full-continuous operation – and the lounge and galley (which are in one space) are on par with owner-operated inland vessel, meaning a very high standard. It is a policy of Sendo Shipping that they can retain their workforce for longer if they provide nicer living spaces, so what they spend on the interior is probably saved on recruiting costs. The heating of the accommodation is with electric floor heating from Speedheat. Local air-conditioning units provide cooling in summer. The heat pumps for airco units are mounted in the aft engine room, which is sufficiently cool due to the absence of diesel engines. The air-conditioning and ventilation installation was done by Windex.

The wheelhouse is a modern yet functional workspace

The comfortable interior is on par with those of owner-operated inland vessels

Throughout the vessel, deck hatches have been installed above the main components. This means that any critical component, be it a diesel generator or a thruster motor, can be replaced within a day. The wheelhouse, which is mounted on a telescopic pedestal, is engineered so that it can be used as an attachment point to pull up a load of up to 5 tons.

Each vessel of the Sendo Liner fleet takes about 100 trucks off the road, with much less overall fuel consumption and manhours. A roundtrip Rotterdam – Groningen – Rotterdam takes about four days, and there is a departure six days a week. Until 2020, the exhaust emission standards are not yet as stringent for inland ships as they are for trucks (Euro 6), and therefore Sendo Liner does not have an exhaust aftertreatment system installed, but due to the efficiency of the ship, the emissions in grams per ton kilometer, are still a lot lower than for trucks. In the design, there space is already reserved for a catalytic converter and a Urea tank. Sendo Liner has two larger ships under construction in China, which are based on the same hull shape and modular diesel-electric propulsion system. Interestingly, the decision to build in China is more driven by delivery time than by costs, as the cost differential is now much less than it was a couple of years ago.

With their electrical propulsion architecture, these vessels are ready for the future. Perhaps someday in the future, a company will lease containers with batteries, charging only a fee per kWh used. This would allow 100 per cent emission-free operation with almost no changes to the vessel. Even today, Sendo Liner will operate partly as pure electric vessel, and most of the time with only one 400 kW diesel generator running well loaded.

Bruno Bouckaert