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Rise of the TOWBoTs

Ship & Boat International: March/April 2016

Even at this early stage of marine drone technology adoption, two key drivers have emerged as the most significant impetus for the development of remote-controlled, unmanned vessels.

The first, which has especially captured the imagination of the small ferry sector (see page 46), is related to achieving a reduction or re-utilisation of onboard manpower; the second, more commonly demonstrated by operators of naval, patrol and SAR craft, involves shielding human crew from risk and injury when undertaking dangerous or dirty tasks. Obviously, these drivers are not mutually exclusive ­ for instance, as remote-controlled and autonomous ship tech eventually spreads to the larger, ocean-going vessel sectors, both factors will be welcomed for their ability to boost health and safety management whilst driving down costs. And there is no doubt that the ferry sector would be loath to sacrifice health and safety considerations for the sake of a few extra bucks.

However, for Canadian tug design expert Robert Allan Limited (RAL), the safety factor has proven the more crucial of the two considerations, spurring the development of its new breed of Tele-Operated Workboat or Tug (TOWBoT) remote-controlled vessel. The first of this series, monikered the RAmora 2400, proposes a 25.8m loa, totally crew-free tug, equipped and classed to Fi-Fi 1 standard, and capable of fulfilling a wide range of tug tasks ­ from operating in the tricky and confined environments of LNG terminals, to comprehensively tackling raging fires ­minus the risk of injury to personnel.

Riskier operations
“The RAmora is designed primarily to take on riskier ship-handling operations, such as bow tug operations with a ship at speed,” Vince den Hertog, vice president for engineering at RAL, tells Ship & Boat International. “The RAmora is also an option for ship-handling operations at terminal locations where toxic or explosive gas leaks would otherwise require a crewed tug to abort a critical ship-handling job with a tanker. “It’s a powerful fire-fighting asset; because the RAmora has no crew, it can be sent into a toxic or explosive situation as early as possible, before it is deemed safe for a crewed fire- fighting vessel to respond.”

Of course, it doesn’t take a blaze for tug operations to pose a risk to crew safety. “The potential accidents we are talking about, at least with respect to ship-handling, involve collisions between the tug and vessel, and tug capsize scenarios that can be a consequence of the collision or can be caused when the tug is pulled over by its own towline also known as ‘girting’,” den Hertog continues.

Girting (sometimes referred to as girding, girthing or tripping) can occur very rapidly, occasionally robbing crew members of the opportunity to escape in time. The West of England P&I Club, which has drawn attention to this long-running potential hazard, describes the girting process as thus: “A towline under tension will exert a heeling moment on the tug if the line is secured around amidships and is leading off towards the beam. As with any vessel which heels over due to an external force, a righting lever is formed as the centre of buoyancy moves towards the centre of the tug’s underwater volume, countering the heeling moment and pushing the tug back upright.

“However, if the force in the towline is sufficiently powerful, it may overcome the tug’s righting lever and cause it to girt. Moreover, it should not be assumed that the winch or winch brake will render or that the towline will break before a potential girting situation occurs, as less force may be required to capsize the tug.”

When working at bow during ship-handling tasks, a tug is subject to a number of risks; den Hertog summarises the main factors:

  • There is a higher propensity for the tug to be drawn into the bow or side of the ship, particularly at the shoulder, due to the hydrodynamic interactions that occur when the tug gets close to the ship. This is especially the case with azimuthing stern drive (ASD) tugs, which can be difficult (if not impossible) to steer away from the side of the ship if the drive end gets too close or makes contact;
     
  • there is less reserve power available to the tug to manoeuvre out of harm’s way should something go wrong, since the majority of the tug’s power needs to be devoted to maintaining speed;
     
  • there is a greater risk of girting due to the higher towline forces in relation to tug stability; the tug master has less margin for reaction time, as everything happens more quickly; and,
     
  • there is increased likelihood of damage from contact, since both the hydrodynamic forces and kinetic energies of the tug and ship square with speed.

Other, random accidents are harder to account for. Figures released by the US Coast Guard show that, between 1994 and 2014, 50%
of towboat personnel fatalities in US waters were attributed to crew members falling overboard. Falls and slips onboard, crushing,
line-handling accidents and being struck by moving objects have also led to serious crew injuries. It is accidents such as these that RAL’s TOWBoT concept has the potential to eliminate. 

Remote control
So, what will the RAmora 2400 comprise, and how will it operate in practice? The idea is for the unmanned tug to be driven by remote control, either from a shore-based control centre or from a conventional command tug, operating in tandem with the TOWBoT. The RAmora would be operated by one person at a time, following successful completion of specialised training in remote-controlled operations. The remote operator will rely on the RAmora console to provide 360degs video and real-time electronic position-sensing from the unmanned tug.

“Both options have their pros and cons,” den Hertog explains. “For instance, on shore, the operator and console can be located in a generously sized, comfortable and quiet indoors space, isolated from distractions. It is easy to switch operators when necessary.

“However, the distance between the shore station and the RAmora can present challenges in terms of maintaining reliable wireless command and control links. On the other hand, a RAmora operator located on a nearby conventional tug, or other vessel type, is closer to the action but is also subject to more distractions and, possibly, a dissonance between the motions the operator ‘feels’ on board the vessel where the console is located, and what the operator ‘sees’ from the RAmora-based cameras ­ at least when sea conditions are causing significant motions.”

To this end, the decision to operate the RAmora from shore or from vessel will depend on a number of factors, not least of all the robo-tug’s location, as well as the attitude of the local regulator, den Hertog notes. “Especially at the beginning, a port regulatory authority or ship operator may not accept shore-based operation if a regulatory framework is not in place to define the responsibilities, qualifications and liabilities of a shore-based operator,” he says. “In that case, it might be more acceptable to operate the RAmora from another vessel, since the captain of that vessel ­ even if not the actual RAmora operator himself ­ may be in a position, from a regulatory point of view, to accept responsibility for RAmora operations.”

The remote control system for the RAmora has been developed jointly by RAL and compatriot electronics specialist International Submarine Engineering, and is partly based on the latter company’s Autonomous Control Engine (ACE), which has a proven track record in the ROV, autonomous underwater vehicle (AUV) and unmanned surface vessel (USV) technology fields. The tug will be equipped with Voith Schneider Propeller (VSP) drives, arranged in a fore/aft configuration, thereby providing enhanced manoeuvrability in all directions. These drives were selected to complement the RAmora’s optimised hull form, which has been based on RAL’s RAVE tug concept.
Working alongside an undisclosed class society (for now), the RAmora will be certified to

Fi-Fi 1 notation; the finished vessel will feature a pair of 1,200m3/hr-capacity fire monitors, fed by electrically driven pumps, while the tug’s crane boom can be optionally fitted with a 600m3/hr fire monitor and camera.

Cost implications
RAL has calculated that there will be scant difference between the capital cost involved in producing the RAmora and that of a conventional, manned tug utilising the same deck equipment and propulsive arrangement. The costs of the remote console, the control system and additional cameras, and so on, would be offset by the savings gained in not having to factor crew accommodation space, wheelhouse layout, domestic systems or safety equipment into the final design. None of the RAmora’s operations would require any crew involvement ­ save for dockside maintenance and refuelling, den Hertog says.

In fact, there could be scope for long-term savings by deploying the RAmora. Although den Hertog considers crew wages to constitute “a fraction of the total operating costs”, depending on location and local labour rates, significant savings could be realised; for instance, RAL has calculated that, in Europe, opex savings of 20-30% could be possible. “Also, because the RAmora will be more compact and lighter than a conventional tug of similar capability, and will be equipped with a hybrid powering system, there will be savings from lower fuel consumption, with the bonus of lower emissions,” he says.

However, one can become distracted by focusing excessively on money; as pointed out at the beginning of this piece, cutting back on crew numbers is not the sole remit for unmanned craft. Neither is this concept about doing away with manned tugs altogether, den Hertog is at pains to stress. “We are developing RAmora for reasons of safety for certain ship-handling applications, not to replace crewed tugboats to save money,” he says. “For the vast majority of ship-handling operations, modern crewed tugs will remain the best option, given how effective and versatile they’ve proven to be in dealing with different ships, changing winds and currents, busy port traffic and communications with pilots.

“By and large, a human tug captain can be relied upon to make good on-the-spot operational decisions based on quickly and continually changing conditions. This adaptability makes crewed tugs indispensable for the foreseeable future.”

Old solutions meet new
Developing the RAmora has not been without its share of challenges. “One of the more challenging aspects of operating without crew is connecting the towline,” den Hertog says. “With a manned tug, a deck hand catches a heaving line passed down from the ship and ties it to a light messenger line, which is in turn tied to the heavier towing hawser. The ship’s crew hauls in the heaving line, now with the messenger line attached, which can then be used to pull up the end of the hawser ­ often with the help of a powered capstan or winch.”

On the RAmora, though, something else was needed. RAL originally toyed with the idea of deploying suction pad or magnetic pad technology, as used in automatic mooring systems, which would enable the RAmora to attach to the side shell of the ship.

“While attractive, since it did not involve a towline at all, over time we realised there were several significant pitfalls,” den Hertog recalls. “Firstly, the relative motions between tug and ship would mean the suction pad would have had to be at the end of an articulating arm that would have to reach out to the ship, which would make the system expensive and heavy. Secondly, the tug would have to be so close to the ship when pulling that the effective thrust would be seriously affected by the propeller wash impinging on the ship’s hull.

“Thirdly, tanker operators strongly prefer ship-handling tugs to make as little physical contact with the hull as possible, to reduce the risk of hull damage ­ so, pulling on the side shell of the ship with a force of several 10s of tonnes became questionable.

Subsequently, RAL cast its thoughts back to the late 1970s, particularly regarding the line- handling crane system it had developed for use on the RAL Z-Peller tug range, for the purpose of lifting a heavy hawser to the ship’s crew. “We realised we could probably make a version of this crane also work for the RAmora,” says den Hertog. Returning to the TOWBoT’s arrangement, RAL modified the design, placing the line transfer crane between the winch and the staple and designing a unique, curved staple, to keep the towline close to the deck, which integrates with the crane. According to den Hertog: “To deliver the towline from the RAmora to the ship, a crane boom with a flexible delivery arm at the end is used to position a messenger line to where the ship’s crew can reach it and pull in the towline. Once the towline is secured, the crane boom is retracted into its stowed position with the towline free to slide through the ring.

“Towline recovery at the conclusion of a ship-handling operation is the reverse. A stopper at the towline eye splice prevents the towline eye from passing through the ring, thereby preventing the towline eye from being winched in past the staple.

“This workable arrangement allows high levels of indirect towing force, due to the midship position of the staple combined with the RAVE hull and thruster configuration. The curved staple design keeps the towline close to the deck and leads outboard when pulling to the side, a design that inherently prevents tug capsize. And, due to the absence of a wheelhouse, RAmora has a ‘clean’ deck machinery arrangement ­ this allows a very wide range of fleeting angles for the towline, which is not possible with the majority of conventional tugs.”

Ongoing development
For now, there is still much to be done during the RAmora 2400’s design development phase. RAL intends to use a tug bridge simulator as a ‘test bed’ for the RAmora console, with which its developers can trial various display configurations for live video and graphical user interfaces (GUIs). “A major objective is to provide the remote operator with enough ‘tele-presence’-related feedback to enable them to operate the RAmora on the basis of 2D information, in the absence of the usual visual 3D and other sensory cues, such as sounds and motions,” says den Hertog.

A year-long proof of concept development phase will ensue, using a free running scale model and focused on operational, rather than hydrodynamic tests ­ a luxury permitted by the already-proven nature of RAL’s RAVE tug-styled hull form, in conjunction with the configured VSP drives. This phase will then conclude with a round of tests on a full-sized RAmora prototype.

Technically, given the backbone of the ACE-influenced control system, the RAmora could be further fine-tuned to operate autonomously. The question is, would this benefit operations significantly? In den Hertog’s opinion, much more development would be needed to ensure a safe autonomous solution. “Ship handling, especially as a bow tug, is a very dynamic operation given how close the ship is, the fact that the towline needs to be monitored and managed constantly, and how quickly the RAmora needs to respond to contribute forces in different directions during ship handling,” he says. However, he does not write off the possibility of future autonomous tugs, adding: “On the other hand, for other operations that the RAmora or future variants would be capable of ­ such as tanker pull-back operations,long-distance line towing or oil spill response ­ a higher degree of autonomous operation is completely feasible.”

These are exciting times indeed for smart ship development, especially given the possibilities that exist for small-to-medium-sized vessel development. Now, the industry needs to proceed with due care and the utmost attention to detail. “The key to winning the industry’s trust is recognition of the responsibility that the developers and early adopters of remotely operated workboats bear in keeping safety the number one consideration over cost,” den Hertog concludes. “If we do not step very carefully, one or two negative incidents could see industry acceptance of remotely operated vessels set back by years.”

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