A Tribute to Dr Neil Hogben FREng - The originator of Global Wave Statistics

We were sad to hear of the death of Neil Hogben, who died on 7th August 2019 at the age of 96. An indefatigable and single-minded researcher who imparted his keen enthusiasm to those working with him, Neil was the guiding force behind numerous research projects, an active member of many technical committees and contributor at conferences, and was responsible for some 200 reports and papers, as well as two major reference books. It was a pleasure and privilege to work with Neil during his long and distinguished career.

Neil in 1998 with a poster commemorating the 1944 liberation of Narni.
Neil in 1998 with a poster commemorating
the 1944 liberation of Narni.

Educated at St Paul's School London between 1937 and 1942, Neil was called up for war service in July 1942. He later wrote about his war experiences as an artillery signaller in Italy and Austria in an engaging war memoir entitled 'Memories of an Unknown Soldier: Recollections of Army Service during the 2nd World War'. Neil was demobbed on return to the UK in April 1947, and then studied for a BSc and PhD in the Naval Architecture Department of Newcastle University (which was then King's College, Durham). He is still remembered there as someone with a passion for old cars who carried out a lot of ship model tests.

Neil joined the National Physical Laboratory (NPL) Ship Division at Teddington in 1955, and moved to the new offices and ship model testing facilities at Feltham soon after they opened in 1959. He continued to work for Ship Division and its successor, the National Maritime Institute (NMI), until he retired from full time work in 1983, rising to the Scientific Civil Service rank of Deputy Chief Scientific Officer on his research merits. After retirement, Neil continued to work for the privatised NMI Ltd, and as a consultant to its successor, British Maritime Technology (BMT), until the mid-1990s.

Highlights of Neil's research career now follow, roughly in chronological order.

Ship Seakeeping Trials & Ocean Wave Statistics

Soon after joining Ship Division, Neil was invited to take part in a research programme on seagoing qualities of ships, undertaken jointly with three other UK research organisations. Neil joined the trials party on board the weather ship Weather Reporter. The ship was instrumented to measure wave heights and vessel motions, and was taken to the North Atlantic in the autumn of 1959. Similar work was done on the Cairndhu on passage to and from Montreal, with Neil again in the trials party, and on the research trawler Ernest Holt. These investigations resulted in important advances in defining sea conditions and modelling ship seakeeping behaviour. Thus began Neil's lifelong interest in the ocean wave environment.

A follow-up research programme started in 1961 with the aim of providing statistical information on wind and wave conditions worldwide, especially on shipping routes and fishing grounds, and also (with hovercraft in mind) in coastal areas. The information would come from weather ships and visual on-board observations from ships in routine operation. Visual wind and wave data were becoming available by this time along many of the main world shipping routes. Neil, with help from Ewing, began work on assembling and collating this vast body of data into a book, eventually published as 'Ocean Wave Statistics' by Hogben & Lumb in 1967. This book became the definitive source of sea state data for many years, representing average conditions likely to be encountered at any time of year in most sea areas around the world.

Hovercraft Hydrodynamics

The National Research and Development Corporation (NRDC) placed an order with Saunders-Roe in 1958 to build the world's first prototype hovercraft, and SR-N1 crossed the English Channel in July 1959. The UK Ministry of Aviation subsequently, in 1961, placed a major contract with Ship Division for a programme of research into the hydrodynamic behaviour of hovercraft, with Neil leading the investigation. Novel model towing arrangements, powering and instrumentation had to be developed, and investigations took place into hovercraft wavemaking resistance and its dependence on trim angle and other parameters. The next five years saw further extensive studies on cushion wavemaking, jet and skirt behaviour in calm water, and further experiments on models in waves. Tests also took place in shallow water, representing conditions that a hovercraft would encounter as it approached a terminal. The MoA contract came to an end in 1964, but research and testing continued for a further few years. Hogben & Everest presented their findings in 1967, in an Aeronautical Research Council report and in papers published by the Royal Institution of Naval Architects (RINA) and Advances in Hydroscience.

Hull Wave Pattern Resistance

From its beginnings in 1911, Ship Division was at the forefront of research on ship hull resistance. Towing tests were performed routinely on ship models to measure the resistance of the hull as it travelled through the water, allowing full-scale ship powering requirements to be predicted, and fuel consumption and hull design optimised.

In the early 1960s, Gadd & Hogben developed a method for measuring the wavemaking component of hovercraft resistance, based on measuring water surface elevations in the wave pattern behind a towed model, then analysing the wave profiles using results from linear wave theory. Neil subsequently refined the instrumentation to allow wave pattern resistance to be measured automatically while carrying out routine towing tests. Several hundred tests were performed on a range of ship models, and initial results were published in a 1975 RINA paper. These confirmed an earlier finding that there is a 'boundary speed' above which wave breaking resistance rises rapidly; ships would not normally operate above this limit. Wave breaking also occurred at the bow in certain cases, dissipating energy into the wake rather than into the wave pattern. In another case, wavemaking resistance increased when the model was self-propelled rather than towed, possibly because of the changed flow around the stern. The authors concluded that further work would be needed before clear inferences could be made for ship design. The results nonetheless gave a glimpse of the design insights that might be gained from tests of this type.

Offshore Engineering

The North Sea oil and gas industry was growing rapidly in the early 1970s, and NPL was invited to act as a national focus for research on environmental loading. An advisory committee known as the Offshore Structures Fluid Loading Advisory Group (OSFLAG) was formed to make research recommendations.

One of the activities undertaken by this group was a review of methods used by the offshore engineering industry to predict wave and current loads on large structures (OSFLAG10). Neil led this review study, and results were published in a 1975 RINA technical monograph. A related 1977 paper by Hogben, Miller, Searle & Ward was published by the Institution of Civil Engineers and was awarded the ICE's George Stephenson medal.

Neil also led a programme of research into wave forces on large monolithic structures (OSFLAG1). Offshore production platforms in areas such as the Gulf of Mexico are usually constructed from tubular steel, with wave and current loads calculated using Morison's equation. New types of monolithic gravity platform constructed from reinforced concrete were being designed for the North Sea, and these large-diameter structures required the use of wave diffraction theory to take account of wave scattering.

A computer program was written under Neil's guidance, to calculate wave loads on gravity structures of arbitrary shape. The program was based on linear wave diffraction theory and became known as NPLWAVE (later renamed NMIWAVE). Model tests to validate the computer predictions were performed on a series of simplified gravity base models in waves, and results were published in a paper by Hogben, Osborne and Standing, presented at a RINA conference in 1974 and awarded the RINA Silver Medal. A follow-up paper was presented at the Offshore Technology Conference in Houston in 1975. NMIWAVE was developed further in the late 1970s, and good agreement was found between measured and predicted motions of tanker, semisubmersible and tension leg platform models in waves. NMIWAVE has since been used for over 30 years to predict wave loads and motions in a wide range of commercial applications including ships, barges, floating breakwaters and wave energy devices.

NMIMET & Global Wave Statistics

Increasing quantities of measured ocean wind and wave data were becoming available during the 1970s, but the results did not always correlate well with wave height and period statistics shown in Hogben & Lumb's 1967 book, which were based on visual observations by mariners. Visual estimates of wave periods were particularly unreliable, and visual estimates of average wave height were sometimes high compared with measured values, agreeing better with measured significant wave heights. Neil therefore began work on a new wave climate synthesis model, which became known as NMIMET. The aim was to provide more reliable and consistent sets of wave height and period statistics than visual wave data alone. Neil outlined his wave climate synthesis methodology in a paper published by the Society for Underwater Technology in 1979. A later paper, presented to RINA, was awarded the Institution's Bronze medal.

Neil (centre) with colleagues in 1982.
Neil (centre) with colleagues in 1982.

Input into NMIMET consisted of the same global archive of visual ships' observations as previously, but the program also modelled statistical relationships between wind and wave parameters to provide wave data of enhanced reliability. Wave period statistics were synthesised from visual wave heights, instead of using visual wave period observations. Wave height statistics could also be derived from wind data in cases where visual wave height information was unavailable or unreliable. NMIMET was then validated against measured data from sites in the North Sea, North Atlantic, Pacific Ocean and elsewhere.

A major re-analysis of worldwide visual wind and wave data then began. The analysis was masterminded by Neil, working with Dacunha, Oliver and Andrews, and involved the processing of 55 million observations of wind and waves from ships of passage between the years 1854 and 1984. This massive task eventually resulted in another major new publication 'Global Wave Statistics' in 1986. The new book provided almost full global coverage, and the database was later developed further to provide a PC product and then the Global Wave Statistics Online service (GWSO).

The 'Global Wave Statistics' book, together with NMIMET and GWSO and their underlying methodology, were outstanding achievements by Neil and his co-workers, and have served the needs of designers of both ships and offshore structures well for over 30 years. GWSO is still available online, and is still actively used by marine and offshore clients worldwide – a fitting tribute to Neil's foresight.

Later Work

Neil retired from full-time work at NMI in 1983, but continued working actively with NMI and its successor BMT until the mid-1990s. He continued to oversee the development of NMIMET and publication of 'Global Wave Statistics', remained a keen member of the SUTGEF environmental loading committee, and contributed to various papers and discussions on wave climate issues.

Neil put forward a novel method for synthesising time-histories of parameters such as wave surface elevation from their persistence statistics, for use in operational and downtime modelling. This procedure, likened to that of building a 'brick wall', was investigated in a 1987 SUT paper, and was found to be simple, reliable and fast to run on the computer.

He also co-wrote a paper with Tucker in 1994, published by SUT, on the development of sea states during severe storms. Wave growth in severe storms was found to fall short of full development due to the effects of limited storm duration and fetch.

Neil wrote a further paper in 1995, published by RINA, on increases in wave heights that had been reported in the North Atlantic. He reviewed the evidence for such increases and possible causes, and some of the implications for the naval architect. A previous investigation had suggested that both average and extreme wave heights in the North-East Atlantic had increased over the years, without any corresponding increase in local wind speeds. A reassessment of the data confirmed that average heights had increased, but Neil expressed doubts about increases in extreme heights. He suggested a possible explanation based on the influence of swell waves coming from distant sea areas, due to changing patterns of wind speeds and directions in those areas.

Neil also became interested in so-called 'rogue' waves, amid concerns that standard naval architecture and offshore design practices did not take sufficient account of abnormal extreme events. He contributed to a discussion on rogue waves in Faulkner's 1998 SNAME paper on the 1980 sinking of MV Derbyshire in a typhoon off Japan.

Awards

Neil was elected a Fellow of RINA, SUT and of the Royal Academy of Engineering. He received the SUT Oceanography award in 1989 in recognition of his major contributions over the years to wave climate modelling and research. Neil and co-authors were awarded the RINA Silver Medal in 1974 and ICE George Stephenson Medal in 1977 for papers on wave and current loading on offshore structures, and the RINA Bronze Medal in 1984 for a paper on wave climate synthesis worldwide.

Acknowledgments

This tribute makes extensive use of information from David Bailey's book, 'Ships in the Making', Lloyd's of London Press, 1995, about the history of Ship Division and NMI. Thanks are also due to Simon Benson and George Mitchell of Newcastle University for information about Neil's university days.