In Depth: Standard Coaster Converted into Cement Carrier

Image Courtesy: Flying Focus

There’s a saying that out of the following three items on the shipyard’s menu, a client can only choose two: low cost, fast delivery and high quality.

However, there are ways to achieve all three courses and one of them is converting an existing semi-completed hull into a tailor-made solution.

Repurposed

This is exactly what VEKA Shipyard, based in Lemmer, did for their latest newbuiding Cembrook.

There is a number of semi-finished coasters in the Netherlands, which were never completed due to the crisis in the short-sea shipping market. Several of these have been successfully repurposed, for example as a fishfood carrier for fish farming or as a roll-on-roll-off (RoRo) vessel for windmill components.

The latest to add to this growing list is Cembrook, a dedicated cement carrier built for Brise Schifffahrt (Germany).

Cement carrier

Apart from a fleet of eight containerships and one RoRo vessel, Brise has over the years built a fleet of nine cement carriers. All of these feature a completely closed cargo system, which avoids the exposure of cargo to the weather.

Cargo operations are therefore independent of the weather conditions. When stocks are reduced and deliveries need to be done just on time, this is a recipe for success.

Previous cement carriers have been converted from former cargo vessels since 2001, under Brise’s own project management.

Capacity

Near the end of 2014, Brise showed its first interest in one of the semi-finished coaster hulls in stock at VEKA Lemmer. The firm’s initial idea was to convert the unit as usual, by adding the entire cargo system including additional generators on deck.

Gradually, the idea came about to integrate the system more with the vessel by using a common electric grid. This would save weight aloft, which would significantly increase the carrying capacity of the vessel.

It was decided that the hull would also be lengthened for more capacity. In the end, modification works grew to such an extent that Brise contracted VEKA Shipyards for the conversion rather than just purchasing the vessel.

Stability

The keel of the vessel was laid in 2011, but as the conversion involved an increase in draught and length, it was considered as a major conversion with the contract date as a new official keel-laying date.

This meant that the vessel needed to comply with new stability rules, which came to force after 2011.

There was also a requirement that the vessel should be able to beach, as a lot of cargo operations take place in Tilbury (UK), where there is a huge tide difference, and the ability to beach is essential for uninterrupted cargo operations.

Due to the increase in waterline length by 10 metres and the increase in draught by 50 centimetres, the freeboard at the bow had to be raised by one metres. The cargo capacity of the vessel increased from 3,500 tons to 5,100 tonnes.

The naval architects at Conoship designed a raised coaming on the main deck, which contributes to the longitudinal strength and the reserve buoyancy.

After a lengthy feasibility study, weighing various alternatives for the vessel, the best overall option was chosen and a contract was signed for the conversion in September 2015.

Fly ash

The complete loading and unloading system was designed and supplied by IBAU (Hamburg) a specialist in cement handling systems.

The vessel is suitable to load either fly-ash, with a specific weight of 0.8 t/m3 and cement, with a specific weight of 1.6 t/ m3.

The big difference in density means that the carrying capacity is limited by volume for fly ash and limited by weight for cement. Fly ash is a combustion product from coal power plants which is captured in the chimney and sometimes recycled as a material in the production of concrete.

Cargo procedures

The cargo can be loaded in three different ways. The normal was is that the cargo is supplied with a conveyor-built system from the shore and discharged through a chute into a spout. From the spout, two valves lead to a closed duct forward and aft.

To ensure that the cargo slides down the duct – which has a slope of seven degrees – the system uses a phenomenon called liquefaction. When air is injected into a powdery substance, it starts to behave as a liquid, and can flow downwards by gravity. For this reason, the ducts have a perforated bottom plate through which compressed air is forced inside.

To avoid overpressure towards the loading side or the atmosphere, the tanks are kept at an underpressure during cargo operations. From the fore/aft loading ducts, the cargo can be discharged into any of the four cargo holds. Below each filling point in a cargo hold is a four-armed loading system, allowing the cargo to be distributed evenly over the entire cargo hold.

A second way to load is to discharge directly from a truck to any of the four loading points atop the cargo holds. A third way is to use the discharge system to load, by making a cross-connection on deck.

Loading in one go

One of the challenges in the project was using a single central loading spout, with channels at the right angle, and still keeping the air draught below 11.40 metres to ensure passage (in ballast condition) underneath the loading chute at the cement factory for 99 per cent of the time. IBAU modified their cargo hold loading system to reduce the required height.

The central loading spout enables the vessel to be loaded completely in one go, without the necessity to move the ship along the quay to fill each old individually.

After loading, the ship needs to remain in port for about a day to ensure that the cargo is sufficiently set. In this process the air escapes and the cargo becomes denser.

With a radar in each tank, the top surface of the cargo is monitored to ensure that the cargo is sufficiently settled. Sailing with the cargo insufficiently set can be dangerous, as the cargo then behaves as a liquid, with a free-surface effect which is detrimental to the stability.

On Cembrook, the double bottom and the side tanks are used as ballast tanks. Each of the cargo holds has a new bottom above the original tanktop. The new hold bottom is angled by seven degrees, draining towards a central suction point.

The bottom plating has aeration panels to fluidize the cargo. Each cargo hold has a bulkhead on the upper halve of the centerline to reduce the free-surface effect.

Deckhouse

To accommodate the large air compressors and the unloading system, as well as to increase the length of the cargo space by five meters, a new section of ten metres long was added amidships. This lengthening also meant that the vessel required a freefall lifeboat.

A deckhouse was built on top of the main deck, housing a cargo control room, fans and compressors for the air supply to airpanels and cement pumps. Two separate fans with their associated air filters create the underpressure in the cargo holds. A long boom crane from Misti (Arnhem) is installed on deck to maneuver the gangway and the discharge hose.

No HFO

In the engine room, the heavy fuel oil (HFO) installation was taken out, which created the space for the two additional gensets. As all vessels in this series, the ship has a controllable pitch propeller and a shaft generator, which provides the power for the bowthruster during maneuvering.

The hull of Cembrook was originally built in the Czech Republic and was further completed in 2013 at VEKA Lemmer on speculation. The accommodation remained largely unchanged during the conversion, except that the CO2 room was reduced (no cargo holds with dangerous cargo) and this space was used for the HVAC installation and an extra cabin.

The rudder was changed from a standard spade rudder to a Benes flap rudder to increase the maneuverability at low speeds.

The new main engine (Wartsila 6L26 G) was downrated from 1.950 kW to 1.860 kW to allow the use of the gearbox and CPP system that was on stock at the shipyard. The main engine of Cembrook was chosen for fuel efficiency.

In ballast condition, the vessel reaches a top speed of 12.5 knots. When fully loaded, it is 11.5 knots.

For the new generators’ exhaust systems, VEKA installed a pre-insulated exhaust system from Loggers, leading to a quicker installation and less noise and vibrations in the cabins just above.

The yard contracted Wolfard & Wessels to make a complete 3D model of the original casing which became packed with more and bigger exhausts, which necessitated 3D engineering. The electrical installation was done by Werkina, which subcontracted the supply of navigation and communication equipment to RH Marine.

Ballast

An additional ballast pumping unit was installed to ramp up the ballast transfer capacity from 300 to 600 m3/h.

Space has been reserved for the possible later retrofitting of a ballast water treatment system. This will be required from the first special survey onwards (after five years). The delay allows Brise the possibility to choose and install the same system on their entire fleet.

Option

Brise has taken an option at VEKA for two similar vessels, which are still pending confirmation.

Cembrook will operate in the North Sea, while the two other ships are intended for the Mediterranean Sea and the Baltic Sea.

Still in stock at VEKA Lemmer are three more 3,250 tonnes coasters and a number of inland waterway vessels, all suitable to be converted into a fit-for-purpose ship, like Cembrook.

Bruno Bouckaert

This article was previously published in Maritime Holland edition #1– 2017.

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