3-General Arrangement & Human Factors (2012)

General Arrangement & Human Factors GENERAL ARRANGEMENT & HUMAN FACTORS MODULE Edited extracts from: Lamb, T (Editor) Ship Design and Construction S.N.A.M.E., Jersey City 2003 Introduction The arrangement of a vessel is dictated by its role For example there are basic arrangements for tankers, bulk carriers, container vessels, car carriers, cruise vessels, offshore supply vessels, harbour tugs and fishing vessels The corresponding arrangements have developed over time to provide the best compromise for the safe and efficient operation of the vessel While it is unlikely that a design will be a failure as long as the basic configuration is adhered to, arrangement design can make a vessel more of a success and a pleasure to operate A superior design needs to be well analysed and excellent compromise between the various individual systems and configuration requirements for the specific vessel The design of the general arrangement (GA) is one of the most important design aspects and one that must be decided early in the process This is because all other design aspects depend on and must be integrated by the general arrangement Structure must be arranged to suit the general arrangement and lifting appliances (e.g cranes) must be located for efficient use and be integrated into the structure to ensure adequate support and distribution of loads However, the general arrangement designer has to understand the structural designer’s need for structural continuity and the load distribution paths and thus select the correct location for the major space boundaries The major compartments have to be arranged to provide acceptable trim within the various operating conditions the vessel will experience in service Smooth traffic flow of crew (and passengers if applicable) for their normal operation and those necessary in emergency situations, is critical Thus the general arrangement designer must work closely with other designers to ensure that these aspects of the design are fully integrated The development of a GA for a vessel has to result in the best possible combination of all required systems into a single efficient system (i.e., synergy) that provides an efficient ocean transport The designer of a commercial vessel should appreciate that the reason the owner invests in a vessel is to provide a profitable service Thus while crew access and amenities are important, the arrangement for cargo, passengers or service intended, must be the driving focus Motion & Noise Consideration Versus Role The most comfortable position to be located on a vessel in a seaway, relative to motions, vibration and propeller noise is amidships at waterline level Currently, however, many vessels are designed with accommodation aft (or far forward) as possible This provides the best General Arrangement & Human Factors solution from a cargo or service point of view These locations may not be the optimum for crew comfort but is usually adopted to facilitate maximum cargo capacity, ease of loading/discharge or deployment/recovery in service vessels Deadweight Efficiency The sizing of holds, stowage (stores0 spaces and tanks may be a deliberate balancing of cargo capacity, handling systems and access or simply the result of a logical structural configuration All commercial vessels are equipped with ballast tanks but the designer should assure that they are used only when the vessel is partially loaded or empty of payload Ideally when the vessel is in the Full Load Condition it should not require any ballast The cost of transporting nonrevenue earning ballast at Full Load is not acceptable unless beam restrictions combined with a high VCG necessitates it The designer must appreciate that the commercial vessel is first and foremost a revenue-generating tool and any operating cost-savings make the vessel more productive The most important characteristics for a cargo-carrying vessel are deadweight (DWT), cargo capacity and fuel consumption Cargo deadweight is the weight of cargo carried and the capacity is related to the cargo deadweight by the stowage factor (m3/tonne) Typical stowage factors are provided in Table 3.1 It is normal for the stowage factors to reduce as the vessel size increases Thus in Table 3.1 when a range of stowage factor is given, the lower value is for the larger vessel Vessel Type Stowage Factor (m3/tonne) Bulk carrier 1.24 Ore carrier 0.54 Container vessel 0.8 TEU/tonne DWT Crude oil tanker 1.22 RO/RO 0.33 – 0.25 lane metres/tonne DWT LNG tanker 2.02 Product tanker 1.35 Refrigerated cargo vessel 1.35 Multipurpose cargo vessel 1.70 Car carrier 0.35 car/tonne DWT Cruise vessel 0.7 – 0.3 passengers/tonne DWT Cruise ferry 0.45 – 0.37 lane metres/tonne DWT Table 3.1 Typical Design Stowage Factors The vessel should be designed to have the lowest possible fuel consumption as fuel costs in current times may be as much as 55 – 60 % of the annual operating cost Figure 3.1 GA for a 45 metre Canadian patrol vessel (Courtesy STX Canada Marine Inc.) General Arrangement & Human Factors General Arrangement & Human Factors The ballast system of tanks requires segregation from all other tanks meaning only clean seawater in and out Smaller fuel service and settling tanks are usually heated and require locations away from the normally cold side shell The designer should also take care to avoid adjacencies of manned spaces to heated tanks Accommodation Arrangement Design In larger commercial vessel all crew are normally accommodated within the superstructure In smaller commercial vessels and in naval vessels crew accommodation is often completely or partially within the hull Commercial vessels under Australian administration require crew and passenger accommodation to comply with the Australian Marine Orders (AMO) Part 14 and/or the National Standards for Commercial Vessels (NSCV) Part C Section 1, which for larger vessels working offshore refers to the Maritime Labour Convention, 2006 for design guidance and recommendations National regulations state minimum clear deck areas in cabins These are usually exceeded in commercial vessels as it necessary to provide superior amenities as an attractant for personnel to the industry and to satisfy maritime union agreements Figure 3.2 Accommodation GA on an ROV support vessel (Courtesy IMT Marine Consultants Ltd) 4.1 Control Centres Integral to accommodation spaces are control spaces such as the navigating bridge, machinery and cargo control spaces, operations centres, etc These are the main spaces in which the vessel’s crew work and hence spend significant time The design of these spaces focus on human factors to develop the best ergonomic arrangement General Arrangement & Human Factors Figure 3.3 Console configuration and dimensions (Ref ABS Guidance Notes on Ergonomic Design of Navigation Bridges) Bridges on commercial vessels are designed for one-man operation and machinery control centres are often designed for unmanned engine rooms With respect to the design of the navigating bridge it is prudent to consider the height-of-eye (1.6 m) of a standing adult The helmsman and watch-keeper must be able to view the sea surface 1.5 ship-lengths forward of the forward perpendicular and at a greater distance in high-speed craft for safe operation The designer of a vessel’s general arrangement should recognise that these aspects of accommodation design are specialised and should work with manufacturers or suppliers of the integral systems in order to produce an optimal arrangement General Arrangement & Human Factors Figure 3.4 Bridge general arrangement for an ROV support vessel (Courtesy IMT Marine Consultants Ltd) Figure 3.5 In-hull accommodation area on a RNZN offshore patrol vessel (Courtesy BAE) General Arrangement & Human Factors Mooring Arrangements & Deck Installations Deck installations includes a broad range of items of structure and hardware normally located on the weather deck to perform various functions such as mooring, cargo handling, etc It must be appreciated that no vessel functions in total isolation and that at some point it is required to interface with shore-based infrastructure, such as berthing alongside, loading/discharging cargo and/or passengers, stores loading, refuelling, etc These aspects of the vessel’s operation are key to its success and hence the general arrangement should readily facilitate their function 5.1 Anchor Arrangements All vessels are required to carry at least one anchor for anchoring in a seaway and if the vessel is classed it will comply with the Equipment requirements of the classification society For oceangoing vessels generally anchors are required in an easily releasable arrangement and a spare anchor stowed in a practicably accessed position Size of anchor and its associated chain specifications are determined from the classification society rules 5.2 Mooring Arrangements Mooring arrangement covers the layout and equipment used in mooring a vessel alongside a berth or to a buoy Over time an acceptable configuration has been developed and it is based on arranging mooring line handling systems to provide to 12 (or more for very large vessels) mooring lines on either side of the vessel These lines are termed as follows: Bow (or head) line Forward breast line Forward spring Aft spring Stern breast line Stern line These six are used for normal weather and the higher number for heavy weather Mooring equipment falls into broad categories, mainly those featuring constant-tension winches which permit automatic constant adjustment of lines where changes in draft or tide is significant, and those mooring arrangements in which lines are manually adjusted periodically when necessary The minimum number of winches on larger vessels is 4, all of the same size, and on the largest vessels On moderate-sized or small vessels this may be reduced to (one forward and one aft) and similarly on small/medium-sized vessels where stern deck arrangements preclude a conventional arrangement The general arrangement of mooring systems, including components such as fairleads and mooring bitts needs to be reconciled with structural considerations Forces imposed on mooring system components are not insignificant and means of distributing loads imposed into the vessel’s hull structure requires provision Safe means of manual handling mooring lines under tension requires adequate clear spatial requirements around both machinery, leads and bitts and should never be dismissed as petty detail in the design of the general arrangement for areas dedicated to mooring operations Figure 3.6 illustrates a very typical forward deck general arrangement of mooring equipment and the required essential clear deck areas are evident General Arrangement & Human Factors Figure 3.6 Forward deck mooring arrangement for a polar research vessel (Courtesy Lürssen Kröger Werft) Human Factors Human factors is the comprehensive term that covers all biomedical and psychosocial considerations applying to the human in the system Decades of engineering practice have undoubtedly proven that the human operator is a complex variable that warrants significant consideration during the first stages of design and throughout the entire operational lifetime of a system Human factors, however, are frequently neglected during the design process When human factors are not adequately addressed, personnel are at risk of making errors and safety is severely compromised because equipment and systems which are not well designed to meet the human physical or cognitive capabilities force individuals to adapt to the system When treating a vessel as a system it may be observed that the central component essential to the success and operation of the system is the human Certainly computers and automated systems have replaced humans in many functions, however the fact remains that humans ultimately are responsible for a vessel’s safe and effective operation It is with this mindset that the designer needs to consider how the human will be able to perform within that system referred to as ‘a General Arrangement & Human Factors vessel’ Designing a system that incorporates human factors into the design criteria from the earliest stages creates an optimal environment for maximum human performance and has a direct impact on inherent levels of safety From a wider perspective, human factors engineering results in a more economical and affordable system, equipment or facility, with reductions in system costs, both acquisition and operating Human factors engineering addresses the human-machine interface which is defined as any direct contact with hardware, software, etc., that use any of the human’s sensory receptors and motor responses The navigation bridge of a vessel is the most obvious illustration of the seaborne human-machine interface Human performance must be measured by considering workload, attentiveness, situational awareness and the timeliness and accuracy of actions One factor that significantly affects human performance and increases human error is fatigue Fatigue impairs performance in many ways and design elements or features that reduce or prevent fatigue are essential to a successful design 6.1 Illumination & Vision Vision is usually considered one of the stronger human capabilities and accounts for as much as 70% of a human’s information acquisition Designing systems that account for the human’s visual abilities entails provision of lighting systems that are compatible with the diverse requirements of personnel aboard This includes consideration of sources of illumination, placement, reflection from surfaces, glare reduction and intensity of illumination Ideally some form of natural lighting should be incorporated into the design wherever possible Artificial lighting is most prevalent within the confines of a vessel where natural lighting is impossible to attain Lighting characteristics have a profound effect on the human biological clock and sleep cycle and is a determining factor in how the body regulates its circadian rhythms On a vessel the majority of the crew spend their time below deck where electric lighting is employed This is problematic and usually creates an irregular and changeable sleep cycle that can easily lead to fatigue 6.2 Noise & Hearing Hearing is regarded as the second most used sense Noise is basically defined as unwanted or undesirable sound It is present in most compartments of a vessel and it is virtually impossible to escape Noise emanates from countless sources including engines, pumps, propulsors and airconditioners There are a number of human physiological and physical impacts of noise in the work environment and all negatively affect human performance and cause fatigue Noise does not have to be extreme or damaging to induce performance degradation Noise can also be a source of annoyance in instances where the noise level is well below exposure limits but degrades concentration Guidance on noise levels is available but focuses on the prevention of hearing damage from high intensity noise However, low intensity noise must be considered as it can also affect human performance and can severely affect sleep Noise reduction management is a significant criterion in the design of any vessel Audible noise is categorised into types; airborne and structure-borne Airborne noise causes stress and hearing loss Structure-borne noise causes damage to machinery and structure There are different methods of reducing and minimising the effects of noise: General Arrangement & Human Factors Source Control Sources of noise occur from vibration, impact, friction and turbulence Vibrating machinery noise may be reduced by techniques such as resilient mounting and avoiding resonant frequencies Friction-induced noise may be reduced by lubrication or precision machining Turbulence noise from pipe systems and air ducting may be reduced via streamlining and reducing flow velocity .2 Path Control Noise must travel between the source and the receiver via a transmitting medium In path control, this medium is altered to reduce distribution of noise This may involve lengthening transmission path, enclosing the source, adoption of intervening structure or using absorbent materials .3 Receiver Control The human receiver always has the option of wearing hearing protection, which is by far the most uncomplicated method of controlling noise but not always the most effective as it relies on the user’s discretion and does not address the underlying problem of noise incidence in the first place Although noise is an unavoidable issue in vessel operation, measures can be taken in the design stages to decrease its effects Post-production measures can also be undertaken to reduce noise levels and increase environmental quality for personnel, however, remedial options are invariably more expensive than pre-emptive measures within the design phase 6.3 Vessel Motions & Accelerations Large amplitude low-frequency oscillations below Hz are significant factors affecting human performance These are the motions due to the hull/sea interaction of the vessel and are responsible for a host of physiological, biomechanical and psychological responses that can severely degrade performance of marine personnel Although motion sickness is often accepted as a common element of the maritime environment, it is a debilitating condition that diminishes human performance to a significant extent and may be incapacitating The motions of a vessel at sea induce a variety of effects that can rapidly reduce even the best efforts to a fraction of what they would be ashore on a stable platform Ship motions limit a crew’s ability to perform essential command, control, communication, navigation, maintenance, system operation, etc Current guidance regarding motion characteristics of vessels centres on Motion Sickness Incidence (MSI) rates and Motion Induced Interruption (MII) rates Current research accepts that the vertical component of motion at a frequency of 0.157 Hz is the most nauseogenic A Motion Induced Interruption is defined as an incident where vessel motions become sufficiently large to cause a person to temporarily abandon their task in order remain upright or balanced Guidance on MIIs is given in terms of a frequency of MIIs per unit of time, however, approximating MIIs from a preliminary hull form is a difficult task There are design 10 General Arrangement & Human Factors considerations that may be employed to moderate the effect of motions on personnel or to reduce motions altogether Motion control devices such as bilge keels, fin stabilisers and anti-rolling tanks may be used to reduce roll motion but provide little effect in pitch and heave motions A study for the USCG recognised potential engineering approaches to enhance sea-keeping through prevention and mitigation of adverse motion effects on personnel: Location Relative to the Effective Centre of Rotation Studies have shown the vertical component of motion to be extremely nauseogenic and at offcentre locations on a vessel the rotational motion components give rise to substantial vertical displacements The magnitude of this motion is proportional to the distance from the centre of the vessel and when combined with the vessel’s natural heave motion, seasickness incidence can be expected to increase at off-centre locations .2 Head Movement Minimisation Although this may be accomplished through individual behaviour there are also design considerations Through location of primary displays and controls on a central panel, the necessity for frequent and rapid or large-angle head movement may be minimised thus preventing seasickness .3 Alignment with Hull Principal Axis Because motion sickness is amplified by complex or off-axis angular motion effects on the inner ear, alignment with the vessel’s longitudinal axis is preferred over a transverse orientation and both of these are preferred over diagonal or off-axis orientation .4 Avoidance of Combined Provocative Sources Multiple provocative sources tend to be additive, therefore a variety of visual distortions can be expected to combine with vessel motion to increase both likelihood and severity of seasickness In terms of design considerations optimising arrangement of sleeping quarters may improve sleep quality in rough conditions .5 External Visual Frame of Reference Provision of an external visual frame of reference has long been recommended as an effective means of counteracting the onset of seasickness Conflicting visual and inner ear effects are reconciled to some extent by viewing a stable horizon This of course cannot be accomplished within the confines of a vessel or at night, none-the-less provision of window area within as many accommodation or workspaces as is practicable is recommended 11 ... Marine Inc.) General Arrangement & Human Factors General Arrangement & Human Factors ... design of these spaces focus on human factors to develop the best ergonomic arrangement General Arrangement & Human Factors ... General Arrangement & Human Factors Figure 3.6 Forward deck mooring arrangement for a polar research vessel (Courtesy Lürssen Kröger Werft) Human Factors