In recent years, much attention has been focused on the development of new crewboats and walk-to-work offshore access systems, but crane transfers continue to have an important place in the offshore oil and gas industry
Every year, around nine million passenger transfers to offshore installations are made by helicopter, and an estimated seven million transfers are conducted by sea, but recent incidents have led some operators to re-evaluate the use of helicopters.
Marine-based crew supply encompasses a range of different methodologies including crane transfer, walk-to-work using a motion compensated gangway, step-over (to a ladder or boat landing) and swing rope. Within these basic categories, there are several different transfer methods, all of which aim to bridge the gap between a vessel moving on the sea surface and the tall structure of an installation. Perhaps the most basic is where the crewboat nestles against part of the installation structure, such as a pontoon or ladder, holding itself in place using its own power while the passengers step across. Sometimes, a rope swing is used to help passengers cross the gap. At the other end of the scale, modern designs of hydraulic gangways provide a telescopic link that pivots and extends to maintain a rigid bridge between the deck of the vessel and a reception area on the installation.
However, the use of a crane on an installation to lift a personnel carrier between the decks of the vessel and the installation continues to be widespread, and there are now several types of crane-lifted carriers, including collapsible nets with the passengers holding on the outside, rigid baskets with the passengers standing inside and rigid capsules with the passengers seated inside.
Of the above-mentioned, despite widespread adoption of motion compensated gangways in some markets, crane transfer remains the most common method, accounting for around five million passenger transfers per annum.
Crane transfer practices vary considerably from region to region. In some areas of the world, these practices have changed little in the past 50 years. In other areas, such as Atlantic Canada, operators have collaborated and redefined industry best practice and have gained an impressive track record for safe operations in some of the most challenging environmental conditions. Crane transfer has also evolved in other ways, and recent years have seen the introduction of new carrier designs and new crane and vessel designs, and operational practices have all improved greatly to allow crews to travel with increased safety and comfort. Safe crane transfers rely on collaboration across several disciplines, including lifting, marine logistics, health and safety and asset management
Recent issues of OSJ have highlighted the potential of new fast crewboat designs that, it is claimed, can compete with helicopters for long-range transfers. The designs in question are intended to be equipped with a new generation of offshore access systems, motion compensated gangways that can transfer offshore personnel from a vessel to a platform but may not be suitable for use in every case. However, in some situations – and some weather conditions – a crane transfer may still be required, however advanced the crewboat and its gangway. At the same time, recent incidents in the North Sea have led to a belief that, although convenient, helicopter transfers can be dangerous.
John Spouge, a principal consultant at classification society DNV GL, who co-authored a recent report on marine transfers, told OSJ that, whilst it is probably true that the recent safety record of helicopters has aroused concern, their record overall is good.
“Nowadays,” he explained, “operators have a greater range of options available to them, and they can conduct case-by-case analyses of which are the best, least risk, most cost-effective options for them to use.”
New vessels and offshore access systems of the type that have been proposed for use in lieu of helicopters have a good story to tell, he said, but there are no statistics available for their use to compare with other forms of transfer. What is more, he said, marine transfers involving vessels rather than helicopters remain less well documented than those involving helicopters.
In addition to designs from companies such as Damen and Marcelo Penna Engineering that have been highlighted by OSJ recently, builders such as Austal in Australia believe that new vessels will secure a growing share of the market from helicopters. It believes that large crew transfer vessels with the capability of operating in at least 3 m significant wave heights, including the transfer, are a safer and more economical alternative to helicopters.
Phillip Strong, chief executive at Reflex Marine, which designs and builds access systems that are intended to be safer than conventional basket transfer systems that lift offshore personnel from the deck of a vessel onto a rig or installation, told OSJ that, globally, there has been a strong trend towards marine transfer and away from helicopters.
He put this down to safety and economics and to the flexibility of marine transfers. Helicopters may be able to transfer personnel quickly over long distances, but they cannot also transport cargo and provide logistic support in the way that a vessel can. Vessels also enable large numbers of offshore personnel to be transferred should that be required. “You can’t transport 170 people offshore using helicopters,” Mr Strong said.
Mr Strong said he recognised that motion compensated access systems installed on vessels are gaining ground in the market but cites examples where their use is not always possible, where platforms and crewboats have had to resort to using baskets or more advanced concepts of the type that Reflex Marine specialises in.
He described an example of fast crewboats that entered service in the last two to three years operated by a leading owner in the Caspian – an important market for crewboats – where walk-to-work operations using the vessels’ gangways 100% of the time was only possible in the summer. In the winter, he said, weather conditions were sometimes such that the vessel and client had to resort to crane transfers using Reflex Marine’s Frog system.
“Where methods such as walk-to-work are the primary means, crane transfer provides an important secondary means of access,” he noted. “This can be due to weather limitations, mechanical failure or planned maintenance. Motion compensated gangways are usually very safe,” he told OSJ, “but there have been one or two incidents involving their use.” In most instances, he said, a crane transfer system was essential as a back-up for transfers.
Reflex Marine’s well known Frog has a long track record of safe and effective personnel transfer and is designed to transfer four people at a time. It is ideally suited to low-volume crew transfers and emergency use. Unlike a conventional basket, the Frog provides extensive protection from the risks of personnel transfer – falling, heavy landings, collision and immersion.
The most recent addition to Reflex Marine’s portfolio is the Wave, which has all the advantages of systems such as the Frog in addition to the option of seated transfer. Reflex Marine believes it has the smallest footprint of any rigid basket or device. Another advantage is that it can easily be used in medevac mode with a slide-in stretcher. In case of immersion, the casualty remains above the waterline.
SES design combines high speed with low fuel consumption
As highlighted elsewhere in this feature, several new hullforms have been proposed for crewboats that could can compete with helicopters for long-range crew transport. Others have also been proposed that can achieve higher speeds than conventional designs and do so without a significant increase in fuel consumption.
Among these is a range of surface effect ship (SES) designs from ESNA in Norway, which has developed several high-speed SES crew transfer units that have a cruising speed at 40 knots with what it describes as “very low fuel consumption.”
ESNA’s designs have been developed as a competitor to helicopters and conventional crew transfer vessels. The designs include a 20 m unit and larger SES crewboats offering accommodation for up to 80 passengers and a 40 knots plus service speed. They are designed for operation with boat landings and personnel baskets.
The SES has an air cushion between the two side hulls and rubber seals fore and aft. Air pressure is provided by centrifugal lift fans. The air cushion lifts 80% of the vessel’s weight, which reduces resistance and allows for 30-60% fuel savings compared to conventional monohull crew vessels. The air cushion system also includes an active motion damping system, allowing the vessel to provide safe access to structures offshore in the same wave heights as much larger catamarans or monohull vessels.