Big ‘Titan’ shoulders the contradictions
Mon, 04 January 2016
The Port of London Authority had a conundrum: they needed a vessel with a big pull yet shallow depth, packing heavy lift equipment while subject to air draft restrictions, capable of meeting fast running tides but still efficient enough for general use.
“Not an easy set of demands to marry up,” admitted Ian Ellis of MacDuff Ship Design.
However, the PLA’s new vessel, London Titan, is a good, solid answer to the puzzle of looking after 95 miles of the Thames that runs from Teddington Lock to the North Sea - one of London’s main arteries.
As John Tye of builder Manor Marine underlined: “It’s not a boat you could buy off the hook – it all had to be totally bespoke.”
In fact it took almost a year of stretching the design around the diverse requirements, including in-depth discussions with the crew, before the two-year build phase could begin.
So, while it might appear ‘roomy’ (along with its £7m price tag) the new vessel’s 36.5m by 13.5m footprint has to encompass an awful lot, from deploying maintenance barge mooring buoys to dredging, salvage and debris removal, dive operations, general maintenance and third-party support.
Further, despite the need for a stable platform a common square bow wouldn’t do as Titan has to make headway against 5 knot or 6 knot currents; therefore the vessel has a long, swim end that reaches around a quarter of the way down its length, helping it gain a 9 knot cruise and 12 knot top speed explained Mr Ellis.
Alongside this, muscle is a necessity – in all the vessel has 2,300kW of installed power – but the design had to take into consideration the vessel’s shallow draft, so the solution has been a triple screw configuration powered by Caterpillar C32 1,000 hp engines supplied by Finning. These are complemented by a pair of 383kW C18 auxiliary engines and a C4.4 69kW harbour set.
From the main engines the power is transferred to three Kort 1,500mm diameter fixed nozzles, giving over 30 tonnes of bollard pull. Another big 750mm KT250 bow thruster sits forward, yielding 1.8 tonnes of force. Interestingly, for day-to-day running the three independent Wills Ridley electrohydraulic high-lift rudders are linked but each has its own dedicated control so they can be manipulated separately for finesse – a good point given the scale of the Titan and the sometimes constrained areas along the Thames.
Dividing the power across three outputs also lends itself to efficiency: downstream running might only need one engine, two might be necessary to push up against the tide, while full power will see all three engines working together.
However, it’s obvious that even after splitting the main propulsion three ways, having 1,500mm nozzles sitting in a 2,200mm draft hull wasn’t going to be a simple matter: Mr Ellis explained the aft end had to be shaped almost like a wave underneath, curving to allow the nozzles to be tunnelled into the hull and giving the propellers the necessary depth of water even when the vessel isn’t ballasted down.
The 6.2 m restriction on the air draft presented another problem and meant a careful shaving of the height: a detailed inspection shows that the wheelhouse has been lowered by 300mm by virtue of dropping the ceiling underneath, “we realised the forward day mess area didn’t need as much headroom as aft due to the reduced requirements for linings”, pointed out Mr Ellis.
Moving outside onto the deck, the equipment is as meaty as the vessel itself. A pair of heavy duty SMT Marine KTBO 11/20.1 deck cranes have been placed diagonally opposite each other on the deck. These need a big, high reach, allowing the PLA to work over the top of some of London’s historic bridges (remember, the PLA’s reach extends up to Richmond) and also to manoeuvre a certain amount of Titan’s own equipment: for example they will be used to drop the vessel’s two 18m spud legs through dedicated shafts that run all the way through the vessel and out beneath the hull to help pin the vessel in place. So, these spud legs will provide a quicker, easier alternative than deploying Titan’s full, four-point mooring system.
But as these are necessarily long, keeping within the air draft has taken quite a bit of thought.
The cranes have a knuckle and three extensions giving 31 tonnes at 7.5m outreach or 11 tonnes of lift at a 20m, while still being able to tuck themselves down close to the deck during transit which helps with both airdraft and navigation: further, there’s an option of using grabs attached to the fixed hook. Underneath, the cranes have a pair of 210kW powerpacks feeding the hydraulics.
At the front the vessel has heavy duty rollers but above this there are also fittings for a solid, 120 tonne capacity A-frame, “useful for very heavy lift work over the bow” said Mr Ellis, especially since Titan will need to be capable of hauling wreckage and debris from the bottom of the river.
This A-frame is part of the MacDuff design: on removing a section of the fender a slot opens up that allows the A-frame to simply drop into place, once again using the forward crane. At the rear of the vessel is a smaller, integrated A-frame, although this is still large enough to take on a 14m plough dredge – another Thames maintenance necessity.
The big pull for this deck gear is provided by a mammoth 120 tonne, two-speed winch which has been placed amidships and close to the centreline. However, for less onerous tasks there are also a number of other winches and pins – for example, a pair of 20 tonne winches provide efficient pulling power at lower loads, there’s also four, 10 tonne Gilson units and three 6 tonne hydraulic capstans for quick, fibre rope wrap and release. Underneath there’s another hydraulic pump running from one of the auxiliary engines plus a much needed completely integrated control system, all this coming from the same company: North Sea Winches.
The bridge gives good views of the deck area, and ties together all the vessel’s main functions with the idea that the running should be as simple as possible, keeping the crewing down to five people during operations on the outer reaches of the Thames. The wheelhouse windows offer a commanding view over all operations and they are fitted with 11 maintenance free External Durowipers Pantographs complete with a 3 year warranty. For those few corners not served by direct vision there is also a CCTV system on the bridge.
However, there were few surprises presented by the finished vessel with Titan’s completed 550 tonnes lightship displacement being within the original prediction despite several changes during the build process.
Interestingly, though it’s 174,000 litres of ballast tanks are essential to getting under the bridges and useful for trim when using the A-frame at the bow, it’s not as critical as one might expect for working over the side - even during a tandem lift.
“I watched while a 5 tonne weight was moved right across the deck for the Lloyd’s Register stability tests and the vessel shifted by only 20mm, I’ve never seen anything like that before,” said Mr Ellis. “The vessel was as good as stationary.”
This new £7m vessel obviously represents a substantial investment for the PLA: in fact its biggest for two decades. However to put it in context it’s useful to remember this stretch of river is home to the UK’s second biggest port - handling 44.5 million tonnes of cargo each year - and it is also the country’s busiest inland waterway, carrying over 5 million tonnes of goods and materials, keeping over 250,000 lorry trips off the roads and used by almost 10 million tourists and commuters a year.
Further, while its design life is an ample 25 years the two older boats Titan is replacing - 1960s built Hookness and Crossness – have, under the PLA’s care, gone on for nearly twice this time. Given the same level of attention there’s hope that London Titan will be around for a similarly long time.
Source: Stevie Knight
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