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Trailer CAT takes shape

The Naval Architect: April 2016

Trailer CAT project manager Claus Kruse, an independent maritime consultant and naval architect, says that the design of the trailer carrier is merely a part of the project and the ship itself must be allied with port and logistics designs that will support the vessel and offer its customers a cheaper and more efficient route for cargo transportation.

The Trailer Cat has been initiated by naval architects OSK Shiptech, transport planning company Transmar, and Claus Kruse. The challenge for the team, which now also includes the Danish Technical University (DTU), class society Bureau Veritas (BV), cargo handling equipment supplier MacGregor, transport planning companies Tetraplan and Copenhagen Business School, is to develop a trailer ferry that meets modern requirements in terms of new regulations, including emissions regulations and the need to reduce unit costs as competition from road and rail services increases.
Currently, the ro-ro industry operates with a design concept that has been around for more than 40 years. Conventionally designed larger ro-ro vessels are very time consuming to load and discharge via a stern ramp into the main deck and via internal ramps to the other decks.

In effect, an 8,000 lane metre (lm) ferry can take six or more hours to turnaround in port so the Trailer CAT team have designed a vessel which halves the loading time, allowing the vessel to reduce speed when it is at sea and thereby reduce emissions and save fuel at the same time.

The project is looking at two possible routes for the vessel design, one on the North Sea and the other between Texas, US, and the State of Veracruz, Mexico. The routes are chosen for the development of two sample business cases for the Trailer Cat Concept.

In both cases, the ports will need to build a linkspan that will be long enough to handle the Trailer CAT as well as have a two tier unloading system that will allow the vessel to load and discharge cargo rapidly from the side of the vessel. Transverse loading and a lack of internal ramps allows more truck masters to operate and significantly reduces their waiting times, effectively doubling the speed of cargo handling.

There is an additional need to move to unmanned lashing of cargo trailers in order to further speed up the loading process, and the team are looking at this possibility too. As more time is shaved off the loading process the slower the vessel can operate, reducing the unit costs further.

“The goal for the concept is  to make 50% cost savings per trailer,” says Kruse, “but the reduced price of oil will make that a challenge,” he admits. Though he still believes that the emissions will be significantly reduced, 70% per cargo unit, compared to a conventional vessel.

“This vessel is bigger so there will be lower emissions per unit [of cargo transported] together with the lower service speed and LNG powered propulsion,” he explains. The vessel is a simplified design without internal hydraulic ramps, hatch covers etc. The steel weight of the vessel is very important for the fuel consumption and the price for the vessel, and so an optimisation of the steel structure is an essential part of the development project. 

Kruse admitted that “these ships will require a significant investment in the terminals to accommodate them, there are no existing terminals at which these ships can currently call without essential modifications”.

Although, he also added that the ports that they were in discussions with had recently given the Trailer CAT project a boost: “One of the concerns from operators that we talked to was that the vessel was too wide and that this could cause a problem getting the ship into the harbour or through the channel. But the port operators said that the draught [at 8m] was fine and the manoeuvrability with the propellers on both hulls meant that it was fine at passing other vessels too without other restrictions for other traditional vessels of that size,” explained Kruse.

Investment in the port infrastructure is, however, crucial with the major efficiency savings to be made through the transverse super-fast loading and unloading. That means that there will need to be a longer linkspan at the port to support the loading operations and this is being looked at
by MacGregor.

Designing the vessel has also posed some challenges for BV, who have had to make original calculations of loads on the steel structure of the vessel. “There are no existing rules for this type of vessel,” explained Kruse, so BV especially needed to make the calculations to check the torsion on the structure between the two hulls and to look at slamming of the hulls.

The preliminary results have shown that there is no serious torsion problem between the hulls. The vessel will be completely designed in steel, but as an alternative the team is also looking to reduce the overall weight/price of the vessel by using light concrete or composites in the construction of the decks. Students from DTU will be studying this problem.

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