Safe Return to Port implications

Tryphonas Petrou CEng MIMarEST uncovers the unanticipated challenges of SRtP on the design and operations of passenger vessels with limited manning.

The Safe Return to Port (SRtP) regulations apply to all types of passenger ships of 120m in length and above or having three or more main vertical zones. These broad limits encompass several passenger vessel types from ferries to cruise ships and expedition vessels to passenger yachts carrying over 120 persons, each with their own design characteristics, operational areas, and manning levels.

A timely response

The SRtP regulations require that actions be completed in a timely manner (less than 60 minutes) but the interpretation of this varies from meaning any single action, to all actions. The Bahamas Maritime Authority (BMA) has tried to clarify this by requiring restoration of the propulsion and safety systems in one hour and those related to safe areas in two hours. For cruise ships with relatively high manning levels, this can be a challenging goal to meet, but for vessels such as passenger ferries and ROPAX where manning tends to be lower, this is harder to achieve, putting a higher burden on the crew. 

Certain vessel types such as those operating in polar regions, must also be designed to meet other regulations, which in turn may have an impact on the complexity and extent of some systems related to SRtP. For example, those vessels in polar regions require extensive heating arrangements that are not utilised on other designs, and with this likely comes additional crew interventions.

To avoid over burdening the crew in SRtP response, a new focus must be placed on introducing efficiencies in systems to reduce the number of crew actions required, and not overlook the fact that even a small number of actions per system, can lead to a significant number overall.

Striking a balance

Different strategies have been developed and implemented by designers to reduce the number of crew actions. One such solution is the extended use of automation such as installation of remotely operated valves which allow central control, reducing the crew effort, but the cost and complexity of that system may be significant as it must too be redundant in line with the SRtP requirements. Moreover, to ensure reliability and safety, a manual back up should be provided which negates the benefit gained if it is required. 

A simpler approach is the protection of components and connections which can be useful when pipes and cables are passing through spaces that are damaged by fire. However, this comes at a cost of either routing by A-60 bound trunks, or using pipes of sufficient thickness, and fire rated cables or fire protective coatings.

Simplifying the redundancy by splitting the vessel into dedicated areas related to certain services, whereby, for example, areas are dedicated to the forward engine room and others to the aft engine room can be beneficial. By ensuring there is no cross over between these areas, it can be assumed that when one area is affected that the service is lost and crew containment and restoring actions are not required to meet the SRtP requirements (as the other redundant area is unaffected). This concept is more straightforward for systems such as power and propulsion that can be more readily divided whereas others such as potable water distribution that span multiple decks and fire zones can be more challenging to achieve. The negative aspect of this approach from an operator’s perspective is the assumed high loss of functionality even for a small casualty.

An alternative solution which is acceptable to the BMA may involve the splitting of the crew manual intervention into high and low-level responses. During the high-level response, all the necessary actions to contain the damage and restore the power and propulsion are to be carried out first. Then, the crew can concentrate on the low-level actions to bring other systems back on-line that are required for the SRtP voyage. This may include heating, cooling and sanitation provisions for specific areas onboard.

Digital tools and crew training

The available manning combined with the response time required to restore operation after a casualty should be part of the SRtP essential systems design. A computer based SRtP assessment can assist to identify the most demanding action scenarios and provide useful feedback to the designer for further system optimisation. Different design and response strategies as discussed above can be checked depending on the number of crew available. 

Based on my personal experience accumulated through assessing SRtP designs of different types of passenger ships over the years, more intelligent solutions could be implemented onboard such as digital tools, assisting to assess the extent of the casualty in systems’ operation and provide alternative solutions related to the actual systems set up onboard. In conjunction with regular crew training on different casualty scenarios, this would be beneficial as part of the ship management policy.

Tryphonas Petrou CEng MIMarEST is Senior Mechanical Engineer, Safety at Sea

Have you read Redesigning the cruise ship post-COVID by Gareth Hamblin CEng CMarEng FIMarEST?