By Clay Evans, maritime historian and retired Canadian Coast Guard lifeboat coxswain

Over the last 100 years the forum provided by the IMRF has served as an international clearing house for evolving information on maritime SAR innovations and new technologies developed by its member organisations.

A prime example of the value of sharing information in an open format is the introduction and development of inflatable rescue craft.

The concept of a “rubber boat” was not new in the 20^th Century. In fact, two submissions for the Duke of Northumberland’s Life-boat Design Competition in 1851 included a craft “made of gutta percha”, or rubber, designed to be rolled out on the beach and inflated, as well as a metallic “Tubular” lifeboat that was deemed to be unsinkable.[i]

The use of small inflatable boats, for both survival and military operations, increased exponentially during the Second World War largely due to their light weight, their relatively small size when stowed and their ample positive buoyancy.

By 1963 and the 9^th International Lifeboat Conference (ILC) in Edinburgh, the inflatable rescue craft was coming into its own as a primary tool for coastal SAR organisations. At the ILC, the Société des Hospitaliers Sauveteurs Bretons (HSB) from France presented a paper entitled The Use of Inflatable Boats as Life-Boats outlining how, from the early 1960s, they had been using small (4.6m) Zodiac Mark III soft-bottom inflatables as seasonal “inshore rescue boats” along a vast number of the country’s tourist beaches. The inflatables were perfectly suited for the role as they were extremely stable, light enough to be hauled on a trailer, required a small crew and minimal maintenance. They were also fast, highly maneuverable, essentially unsinkable, relatively cheap to build, perfect for coming alongside vessels in a rough sea and low enough to easily recover persons from the water.[ii]

An early Zodiac Mk II inshore rescue boat of the Société des Hospitaliers Sauveteurs Bretons (HSB) circa 1961. Credit: SNSM

The French IRB program was so successful that, by the year of the conference, the HSB and the Société Nationale de Sauvetage en Mer (SNSM) had 90 such stations in France. They were already experimenting with the use of inflatables year-round at certain locations and as auxiliary craft to larger conventional lifeboats. After 1963, other lifesaving services had adopted inflatable boats for use as rescue craft, most notably the RNLI, who developed a 4.9m inflatable boat, which became known as the “D” Class rescue craft. By 1966, there were 72 of this type in service around the UK and Ireland and they had already been launched 1,449 times, having saved an estimated 613 lives.[iii]

The next significant stage in the development of inflatable rescue craft was the introduction of a rigid hull to the inflatable collar. The advantage of a rigid hull over the conventional soft bottom, with wooden or aluminium floorboards was that it avoided the potential for the deck and bottom to buckle in a seaway, as well as providing a much finer entry and resultant ride for those onboard.

The RNLI is credited with building the first prototype rigid hull inflatables (RHI), led by a team at Atlantic College in Wales, which was also the home of a RNLI D-Class lifeboat station. Various hulls were tried and eventually the institution settled on a 6.4 m twin-outboard deep-V design known as the Atlantic 21. Not only was this early RHI version extremely maneuverable, it also had enough deck space to carry a stretcher, a self-righting airbag and “waterproof” outboards and due to a flat surface towards the aft part of the keel, could be beached and remain level onshore. Similar designs followed all over the world. By 1970 the number of people rescued by the RNLI’s inflatable inshore rescue boats exceeded that of the Institution’s displacement lifeboats by 702 to 555.[iv]

One of the prototype rigid hull inflatables which led to the development of the RNLI’s Atlantic 21 type. Credit: RNLI

Recognizing the significant sea-keeping advantages of rigid hull inflatables, the next major innovation outlined at the ILCs was the development and introduction of much larger “RHI lifeboats”, which could be used for both inshore and offshore work. The RNLI began initial experiments on larger vessels at their purpose-built RHI construction facility and training centre at Cowes around 1979. In a paper entitled A New Rigid-Inflatable Lifeboat published in the journal Lifeboat International in 1980, principal designer David Stogden wrote that the new vessel was “required to be fast, essentially simple but with outstanding seakeeping qualities”.[v]

Two 12.2m prototypes were constructed, known as the Medina Class, one with an open console and one with an enclosed cabin. Although these vessels proved very versatile, the weight and efficiency of propulsion technology at the time remained an issue and the RNLI did not pursue the RHI lifeboat concept any further, instead focusing on further development of its conventional “fast” self-righting lifeboats.

Meanwhile, the two Dutch lifeboat societies in the north and south had been working with the RNLI on RHI design since a mutual aid agreement had been signed in 1973, including work on the larger RHI concept. In short order they recruited David Stogden to continue to pursue the development of the RHI lifeboat. In 1984, the KNZHRM commissioned the construction of a new prototype, again with a full cabin and in the 12.8m range but this time with water-jets for propulsion. Launched in 1884, the Koningen Beatrix, or KB, became a perfect test-bed for future RHI lifeboats in the Netherlands, so much so that today the KNRM’s fleet consists almost entirely of large and small RHIs.

The lessons learned from the KB experiment were put to good use in the design of the next Dutch RHI lifeboat. The concept for the next stage was done in collaboration with the marine engineering firm of Bureau voor Scheepsbouw de Vries Lentsch for final design configuration. After extensive tank tests, tenders for construction of the first boat were invited in 1986. The first of this new generation of large RHI was launched in 1988 with the launch of the Johannes Frederik, which became the namesake for the type and became otherwise known as the JF Class. Taking advantage of the lessons learned from previous prototypes and the technologies now available, the new vessel proved herself to be a fine heavy weather rescue craft, more than capable of replacing the aging fleet of large steel MLBs, particularly with its top speed of 34 knots.

The KNRM’s first large production RHI Lifeboat, the Johannes Frederic or JF Class in breaking surf. Credit: KNRM

The two Dutch lifeboat societies merged to form the KNRM in 1991 and continued to pursue the operational model of an all RHI fleet by 2002, including constructing smaller RHI types for inshore and carriage-launch work. In 1999, Sip Wiebenga, Director of the KNRM, stated in Lifeboat International, “It is now felt that all the practical problems with RIBs are solved, or under control, and coxswains and crew members express their continuous satisfaction about the capabilities of the RIBs.”[vi]

One technical issue that remained related to weight. In order to keep RHI lifeboats lightweight they carried less fuel on average then conventional lifeboats, thus limiting their range to inshore and nearshore work. The goal was to design and build an RHI lifeboat large enough to safely conduct extended operations offshore. With the same design parameters and design team that built the Johannes Frederic class, it was decided that the perfect length for this even larger RHI lifeboat would be around 19m.

In 1999, the KNRM launched the first of its Arie Visser Class 62ft RHIs - a stretched version of the JF Class RHI lifeboat and one of the largest RHIs in the world. The AV type are powered by two 1,000hp MAN diesels, which produce a top speed of 35kts that can be maintained for 16 hours duration. The lifeboat has improved accommodations, engine room access and greater cockpit space in the stern. The longer hull form offers a softer ride in heavy seas, which helps eliminate crew fatigue on extended offshore calls.^[vii]

The even larger 19 metre Arie Visser (AV) class RHI Lifeboat. Credit: KNRM

One would think that with the success of the KNRM’s RHI program, small, medium and large, that they might have stopped there. In the best interest of continuous improvement, however, they did not.

In 2009 the KNRM started the 'SAR Nh 1816' project to eventually replace the Arie Visser class. In collaboration with the Faculty of Maritime Technology of TU Delft, Damen Shipyards and Willem de Vries Lentsch Yachts Designers & Naval Architects, the team discussed, designed and tested which type of lifeboat could meet the specified requirements in the future.  

The most important points for improvement over the Arie Visser class were noise reduction in the wheelhouse, more comfort for the crew through friendlier sailing behavior in bad weather and the use of modern engines and equipment. 

The first Nh1816 went into service in 2014. The prototype was tested in the field until 2021 and, as with all prototypes, further development continued towards the construction of a Nh1816-2 type which should combine the best features of the Nh1816 and the Arie Visser class.[viii] 

The KNRM’s latest super RHI, the KH1816 Class on display at WMRC 2023 in Rotterdam. Credit: Author

Of course, it is not just in the Netherlands that innovations in inflatable rescue craft technology have taken hold. Other advances introduced by other nations have included more rigid, rather than inflatable collars; the use of shock-absorbing seat technologies; and the use of diesel outboard motors. There are now hundreds of models of inflatable rescue craft on the market with many maritime SAR organisations having standardized versions for different uses.

The rapid evolution and use of inflatable rescue craft for maritime search and rescue, in a span of just over 60 years, is a phenomenal testament to the vision and drive of the design teams, the boat crews and myriad organisations and companies that supported them. There is no doubt that there will likely be much more to this story as time goes on and technologies develop and the IMRF will always be willing and able to help showcase these innovations to enhance both the safety of both those saviours going into harm’s way and those who are in peril at sea.