14 April 2015
This move will most likely result in a need to increase the speed requirement for the landing craft, to ensure that similar quantities of vehicles, stores and personnel can be offloaded within the same, current timeframe. Combine this with the possible safety hazards which must be considered when operating at faster speeds, and the continuing cost constraints that many countries are experiencing and naval architects and engineers are faced with a complex and challenging situation.
Nick Johnson, Principal Naval Architect at BMT Defence Services, highlights the delicate balance between increased speed and cost efficiency, as even the smallest of changes in the needs of the end user can have a significant effect on the design. Nick further explains why it is vital for designers to be fully equipped with all of the knowledge to properly understand the end user's requirements. Without this the best and most cost effective balance between desired capability, operating concept and vessel design may not be achieved.
Typically a Landing Craft Medium (LCM) is used to transport vehicles, stores and personnel from the host ship, for example a Landing Platform Dock (LPD) or a Landing Helicopter Dock (LHD), back to the shore side and vice versa. Historically, the host ship has operated relatively close to land, perhaps 5 to 10 nautical miles away, however, many navies now seek to adopt a concept of operations that offers increased operational and tactical surprise, whilst reducing the vulnerability of the host ship to inshore threats. This inevitably leads to a requirement to launch assaults using landing craft, from further offshore.
This type of requirement presents a number of challenges for nations worldwide and is likely to see a step change in the design of landing craft over the next decade. Firstly, in order to ensure navies can still carry out the offload of their vehicles including personnel and equipment within a certain period of time and from further offshore, there is a strong desire to increase either the speed or payload capacity of the landing craft. In some instances, this could see the introduction of speeds of 40 knots or more, as opposed to around 10 to 15 knots which is the general case at present. Increased speeds will undoubtedly lead to larger propulsion systems which in turn, can result in a payload reduction and therefore, a higher chance of having to carry out more journeys back and forth to the host ship to achieve the same objective.
Operating at higher speeds also presents a number of new safety considerations for the landing craft designer. For example, high speed collision with submerged bodies or grounding. The majority of the traditional landing craft we see currently are not designed to cope with the more severe and extensive damage associated with these high energy collisions, which can result in multiple compartment flooding. Also, being further offshore, landing craft are likely to experience a more variable environment in terms of sea states and weather conditions.
With this in mind, some navies aspire to operate landing craft with levels of safety similar to other naval or commercial craft. This brings into play alternative more appropriate rules for damage stability than may have been applied in the past, for example, a requirement to withstand multiple compartment damage as aforementioned. When this is combined with other requirements associated with high speed operation, it will undoubtedly drive the arrangement of the internal subdivision and intensify the challenge for the designer.
Furthermore, the increase of transit speed requires careful consideration in regards to the human factors aspects of the design. An example is the possible requirement for dedicated, specialist crew and passenger seating - provision of the latter in particular has the potential to severely constrain the payload capacity of the craft if not dealt with carefully in the early stages of the design.
There are also geometry constraints which the designer must consider. Landing craft will usually have a shorter service life than their host ships and not always will both the host ship and landing craft replacement programme coincide. Therefore, despite logic dictating that the host ships should be designed around the landing craft which they carry, invariably, the landing craft must be designed to fit existing well dock dimensions. A further requirement for interoperability across the fleet and amongst allies can effectively freeze the dimensional footprint of landing craft from one generation to the next.
On the surface, landing craft may seem relatively simple vehicles given their role, but a closer look at the environment in which they operate and the tasks they perform shows that the designer faces a challenging task.
Many nations are already looking actively at these challenges and turning to companies such as BMT for design support. The UK in particular introduced the Fast Landing Craft programme which BMT Defence Services played an integral role in alongside sister company, BMT Nigel Gee. Contracted by the Ministry of Defence's (MoD) Defence Equipment & Support (DE&S) team, we developed a novel, tri-bow monohull platform using a parent hull-form derived from an internal research and development programme, which included model tests to optimise performance. This design met the demanding MoD requirements for a FLC with high transit speed and high payload capacity, whilst demonstrating excellent on-beach stability. Understanding how the craft is going to be used is key.
Often designers will be given a specification from the purchaser of the landing craft which will outline basic requirements in relation to speed, size etc. What is rarely provided is how the craft is actually going to be used. The latter of which is absolutely vital in order for the designer to ensure that the final solution provided is efficient and functional for the operator. By determining how the landing craft is going to be used, designers can not only challenge the requirements set out, which is an extremely important part of the designer's role, but fully understand what it is they are trying to create. This knowledge will allow the designers to work even more closely with the capability sponsors to deliver the optimum solution.
As well as working with the UK Naval Authority in developing future standards for landing craft stability, BMT has engaged with a number of key customers and end users such as the British Army to further enhance its own knowledge and provenance of certain design decisions. This has led to a significant internal R&D effort to provide concept designs such as the Caimen®-60 which helps to address the fine balance between increased speed and cost efficiency. Providing a flexible asset for the rapid movement and amphibious delivery of vehicles, equipment and troops from a host ship to the shore and vice versa, the Caimen®-60 is a deliberately robust, low complexity and affordable design that adopts the best of the proven technology of current LCM designs alongside the revolutionary BMT tri-bow platform.
It's true to say that there comes a point where the investment required to achieve a little more speed, exceeds the return in performance. There is little margin for established landing craft designs to absorb minor changes in requirement and still remain cost effective because of the broad range of constraints that govern the design of the craft. It is for this reason that designers must communicate the effect of requirement change on the cost and capability of the subsequent design within the early stages of design and identify opportunities for achieving savings and enhancements. This approach will ensure that the best and most cost effective balance between desired capability, operating concept and vessel design can be achieved and the users have the right tool for the job
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Nick Howes is a Test Analyst in the Information Systems group. His role also encompasses Space SI Research and Development. He was a science writer for the European Space Agency and SKA Telescope projects, and has expertise in orbital dynamics, Imaging systems, and cometary/asteroid bodies.
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