Fast-operated dry dock flap gates are limited to 70-80m wide docks, right?

It sounds cliché but time really is money when it comes to ship repair and maintenance in a dry dock. Conventional wisdom tells us that a large, heavy gate that is slow to operate may be fine for building ships as they are only undocked a few times a year. For high frequency maintenance docking however, we know that our clients want a solution that is much, much faster.

Smaller dock entrances can use a gate that simply spans the entrance, while larger entrances typically need a gate that is gravity-based (ballasted) or propped/cantilevered in some way.

The first of these techniques (ballasted) means the gates tend to be very slow to operate. The ballast needs to be removed to open the gate and there can be thousands of tonnes of water ballast in the biggest gates. The second of these (propped/cantilevered) are typically more expensive to construct, challenging to maintain and difficult to install. Gates of this type may require prop alignment checks to be carried out during each operation, which again slows things down. This, of course, has an operational and financial impact: if you need to open gates two or more times a week and they take hours to open, the hours build up. These hours could be better spent servicing more vessels directly increasing our clients turnover.

It was against this backdrop that one of our long-standing clients – Sembcorp Marine – came to us in 2010. They needed a fast-operated gate, that would be economical to construct and span a dock entrance width of 89m unpropped. A flap gate operated by two winches would be the ideal solution; the trouble was the entrance span would make it the largest of its kind in the world.

We rose to the challenge, and delivered the largest single span flap gate in the world! However, the global shipping industry does not stay in one place for long: Sembcorp returned to us a few years later and asked us to help them with another flap gate for an even bigger dock – this time one for a dock entrance over 110m wide. A new contender for the world’s largest flap gate would be needed.

Pushing boundaries and finding solutions

Whilst we were confident it could be done, we knew we were approaching the strength limits of some of the materials involved and therefore approached this challenge by first conducting a feasibility study. Once satisfied our proposed solutions for such a large gate were feasible, the client gave us the go-ahead and we put together a detailed design. It took less than three years to go from initial concept through design, planning and construction, to the installation of this ground-breaking dock gate structure at the Sembcorp Marine Tuas Boulevard Yard.

The challenges involved in this project cannot be underestimated. Consider the water pressure pushing the gate towards the dock. Some 15,000 tonnes of hydrostatic pressure plus a structural weight of 3,000 tonnes needs to be safely transferred into the docks concrete structures.

Typically, gates would have a meeting face of timber between the steel structure and the concrete walls. Traditionally this would be a hardwood timber, such as greenheart or Ekki, but this would be crushed under the forces generated by such a large gate. Our solution was to use an ultra-high-density plastic, which could cope with this load intensity whilst still being flexible enough to cope with any tolerance discrepancies between the steel gate and the concrete civil works structures.

Another significant challenge was being able to create a gate design that was robust enough to cope with the loads, at the same time as being sufficiently flexible to form a water tight seal with the civil works (concrete). As the gate bends, due to the water pressure, the bottom corners tend to lift away from the concrete as the gate bends in the middle, deflecting in to the dock. This would allow water into the dock, a catastrophic design flaw. We therefore had to determine the perfect balance between strength and flexibility to ensure the gate would remain sealed around all the meeting face.

So how were we able to overcome each of these challenges? Alongside our expertise, knowledge, and experience, we have invested in the development of computer programmes and software that give us detailed insight and analysis of every aspect of the gate, down to individual steel elements. We can use these to predict how even the tiniest adjustments in structure affect different parts of the gate. Put simply, it allows us to know where we can push the boundaries in a design without adversely affecting the integrity and reliability of the gate in order to meet a client’s brief.

In short, we delivered – the largest flap gate in the world – at over 110m in length. It can open in less than 10 minutes, allowing our client to maximise the dock utilisation, thus increasing their turnover and margins.

Additionally, The Institution of Civil Engineers also recognised the achievement of this record-breaking gate – awarding it Highly Commended for Engineering Excellence.

New markets

Ultimately, at Royal HaskoningDHV, we are pushing the innovation envelope to help our clients. The dry dock with the fast 110m flap gate can not only service larger ships and be responsive to short notice requests, but given its size it can also accommodate oil rig maintenance.

While many operators carry out floating repairs on rigs, it’s much easier to carry out maintenance and repairs in the dry in a dock. Thanks to their new flap gate, Sembcorp are now able to diversify their service offering.

What sets us apart

Not only are we innovating and pushing boundaries on gate designs, but we continue to work with clients around the world to find solutions to the full spectrum of challenges in the maritime industry. Our world leading experience and our innovation track record give us the confidence and know how to tackle these challenges.

In an industry fraught with complex technical challenges, our clients trust us to deliver innovative solutions that work and to support them at each stage of their projects.

To learn more about what Royal HaskoningDHV can offer your business, visit our Dock & Lock webpage or contact Richard Bowman