ISO/TS 18683: A good starting point with challenges
In early 2015, ISO published the ISO/TS 18683 Guidelines for systems and installations for supply of LNG as fuel to ships. At present, a number of companies globally are trying to adapt their products and services in line with the guidelines and contribute to the safe and efficient development of LNG as marine fuel. SSPA and its qualified staff have supported a number of these companies in this work. In so doing, a number of challenges have been identified, specifically relating to ship-to-ship operations.
The LNG bunkering facility concept
One very central concept of the guidelines is the definition of the LNG bunkering facility. For shore-based operations, this is a rather straightforward concept, but when it comes to ship-to-ship (STS) operations, the definition of the concept and the reality of the application of the guidelines raises some interesting challenges. Many of these challenges are related to ship motions.
When delivering LNG from a truck or from a fixed storage facility, it is reasonable to assume that the only significant movement that may be induced during an operation relates to the receiving vessel. In addition to this, it is also reasonable to assume that movements of the receiving vessel are limited and usually rather predictable since the vessel should be properly moored in a protected harbour or similar. This makes the definition of the LNG bunkering facility with a clear operational window in line with the guidelines rather simple.
When undertaking STS operations, even in a protected harbour, the number of possible movements and the probability of such movements occurring during the bunkering operation increases significantly. If then moving the operation to an offshore location such as Galveston Roads, the Singapore Strait or Skaw Roads, it is inevitable that ship movements during the operation will become even harder to predict.
The guidelines clearly state that a supplier of a bunkering facility shall, among other things, include information on the criteria used for the design of the equipment and its performance in real operations. For an arm or a hose handling system used for shore-to-ship bunkering, such as at the bunkering facility, this implies that the supplier shall, among other things, include information such as the maximum geometrical window the equipment is able to handle, the maximum acceleration in any part of the system that is allowed, as well as the maximum forces on other structures such as the manifold of the receiving vessel that the equipment may generate.
The problem is that if similar equipment is mounted on a bunker vessel, this information is no longer relevant since it does not cover the movements of the bunker vessel itself and therefore does not constitute the bunkering facility concept as defined in the guidelines. Instead, you have to see the whole bunker vessel, including (but not limited to) the transfer equipment, as the bunkering facility. This raises some interesting and challenging requirements.
When is it possible to bunker?
If looking on this issue from the perspective of a potential STS LNG bunker supplier or its client, the most important question is: – Under what circumstances and in which location is it possible to perform an STS LNG bunkering operation with an acceptable risk level?
To answer this question and to fulfil the requirements in the guidelines, information of how the vessels moves in relation to different external parameters such as wind, waves and current needs to be delivered provided by the supplier.
In addition, the dynamic interaction between the vessels when alongside each other also needs to be addressed to some extent. This information can then be used by the LNG supplier when evaluating the possibility of supplying LNG at a certain location under varying weather conditions and towards different receiving vessels with an acceptable risk level. The complexity of this evaluation should not be underestimated since there is an almost infinite number of possible scenarios.
SSPA has the answers
With 75 years of experience of ship design, ship movements and simulations, SSPA has a large portfolio of movement data covering all kinds of ship types, including a number of LNG bunker vessels. SSPA also has significant experience of risk assessments and simulations in relation to lightering operations in various conditions. In combination with its comprehensive knowledge of the regulatory framework, logistical challenges and risk assessments related to LNG as marine fuel, SSPA has the tools to give accurate answers to the fundamental question raised above.
Photos and illustrations
Illustration: The LNG bunkering facility as illustrated in ISO/TS 18683.
A typical LNG bunkering facility. Photo: Johan Gahnström.
Risk assessments made by SSPA. Photo: Alexandra Bakosch.