Mast Presentation

Editor's Notes

• #3: The work to be presented is part of the Ship-Human Integration Performance System (SHIPS) funded by the Office of Naval Research.SHIPS project lays the foundations into developing an integrated human performance/seakeeping analysis environment that can be used to analyze and maximize ship performance at the ship design phase.
• #4: And there is only one question to be answered: How well do existing standards, used in ship design process, address human performance issues?The underlying reason for this question is simple yet complicated. The constraints of the human element, because, UNFORTUNATELY, the human element still remains the bottleneck of naval systems. The design of future naval ships in the presence of changing environments, rapidly evolving technologies, and operational uncertainty is a major challenge. This challenge is becoming more significant as the demands for seakeeping performance, and mission effectiveness continue to rise as manning is reduced. The effective use of human performance standards is an essential step toward the design of an operational system, especially with reduced manning levels. In naval systems, standards are the primary bridge between the worlds of engineers and human factors. Even though considerable effort has been made lately towards high-fidelity hydrodynamic prediction models, the problem of human performance in a reduced manning environment has not been given the attention it deserves.
• #5: The work presented here will focus on assessing the current state of existing standards regarding the effect of ship motion on motion sickness, sopite syndrome, human activities, comfort, health related issues, motion induced fatigue, and sleep effects. Most of all, we focus on the possible gaps in the guidance provided in the reviewed publications.Given the strong effect of the human element to overall system operational performance, it is important to identify these gaps so that research can focus on them. Increased automation capabilities will not be sufficient to overcome inadequate human performance capabilities that can result from low manning levels combined with deleterious ship motion effects.
• #6: The first step in this work was to identify which human performance aspects we were interested in. Aspects that are known to be related to ship performance as a system.There are a number of taxonomical approaches. For example, Colwell in his review of motion sickness and biodynamic problems in the naval environment mentioned four problems related to human performance versus vessel motion, motion sickness, motion induced interruptions, motion induced fatigue and whole body vibration (Colwell, 1989). On the other hand, the High Speed Craft Human Factors Engineering Design Guide notes a three factor approach based on fatigue, balance, and motion sickness (Dobbins, Rowley, & Campbell, 2008).We approached the problem with the taxonomy depicted on the slide. The initial model proposed in 2005 incorporated MIIs, MSI, Sopite Syndrome, Sleep, and MIF as the major factors effecting performance at sea. At that approach, we combined the existing evidence/ anecdotal data suggestive of sleep disturbances because of vessel motion, and the sopite syndrome which is a point of concern in personnel operational effectiveness (the depiction of sopite syndrome as a component of performance independent of motion sickness is an issue of continuing discussion outside the focus of this study).Based on this earlier approach, we proposed a revised version which integrates the following changes: Comfort is added. Although comfort cannot be considered a significant parameter to human performance (and therefore, to the more central discussion of task performance), it can be a factor influencing passengers’ subjective evaluation of well being. Even at this level, including comfort in the general model fills in a gap of possible interest.Health and safety issues. A sub-taxonomy of the effects of ship motion on human activity, which includes balance disturbances (motion induced interruptions), manual material handling issues, and other effects. Furthermore, for better conceptualization, the integrated components were categorized according to the three criteria of acceptable human vibration exposure according to Guignard & King (1972), which are: The conservation of occupational health or safety against potentially hazardous levels of vibration, The conservation of working efficiency (or performance) against distracting or otherwise disturbing vibration, andThe conservation of comfort or amenity, which intrusive vibration may spoil, for example, in passenger-carrying vehicles.  The slide depicts the proposed model at its current state
• #7: Given the focus of this work, the first step was to gather all possible standards that would potentially fall into our focus area.Although the main focus was on the effects of whole-body motion in the naval environment, other appropriate information was not excluded (for example information on fixed-guideway transportation systems). The initial list included 49 publications of possible interest. These were reviewed and categorized according to their relevance to our main objective. The result of this step was to group the gathered publications in four categories: Withdrawn/ cancelled documents: This group includes 4 items.Guides and other publications: The group includes 15 items which are the least relevant to the focus of this work, but include useful background information (human design guidance for system designing and naval architecture, ergonomics to marine systems, definitions, habitability issues for surface ships, human engineering design data, wave information).Standards and guides at the “periphery”: The group includes 20 items which have some relevance, and address issues related to our main objectives (for example, measuring motion, Core standards and guides: The group includes 14 items referring to human performance aspects of interest, and thus are the main focus of this work. The final step, based on the latter group of “core” standards, was the integration of the gathered information per human performance aspect and the identification of points of interest (for example: utility, generality, constraints, coverage of human performance aspects under focus, gaps, etc.).
• #10: Generally, existing standards address motion and vibration effects on humans in the frequency envelope between 0.1 and 80 Hz. This range is divided into two regions, the lower part being occupied mainly by motion sickness, whereas the higher region being occupied by the rest of the effects (biodynamic interference, health, comfort, etc). Given the publications reviewed, there is a consensus regarding the frequency range of human performance aspects under focus in this study. These envelopes are the following: Motion sickness nauseogenic space: ranging from 0.1 to 0.5 Hz. Health effects: All standards evaluate health effects in the frequency range between 0.5 Hz and 80 Hz. A difference exists, at the lower limit proposed by Directive 2002/44/EC. Although the Directive, refers to ISO 2631-1 and identifies 0.5 Hz as the lower limit, it further proposes that only frequencies above 1 Hz might be considered.Perception of vibration: 0.5 Hz - 80 HzComfort: 0.5 Hz - 80 Hz. A difference exists, at the lower limit proposed by ISO 2631-4:2001, which is identified as low as 0.1 Hz for roll motion. Furthermore, ISO 2631-4:1997 (which refers to fixed-guideway transport systems) address comfort in different frequency ranges based on the type of induced motion: a) roll motion: 0.1 – 2 Hz, b) lateral and longitudinal motion: 0.5 – 10 Hz, and c) vertical motion: 0.5 – 20 Hz.Effects on human activity (hand or finger manipulation control, etc) in the frequency range between 1.0 to 80 Hz.Vision: 20 Hz – 70 Hz or more.Obviously, this list is only a very brief depiction of the vibration induced stimulation on the human body and is based exclusively on the information provided by current standards. Other known effects do exist, like resonance of the various body parts. For example, research has shown that the first resonance for the sitting man is between 4 and 6 Hz, the thorax-abdomen system between 3 and 4 Hz, the resonance peaks for the standing man at about 6 and 12 Hz, the head between 20 and 30 Hz, and eyeball disturbances between 60 and 90 Hz
• #11: Assessing vibration exposure is a challenging issue given that ship’s motion includes transient (occasional shocks) and non transient phenomena, non sinusoidal waveforms, etc. ISO 2631:1997 identifies two motion envelopes where different methods should be preferred. The first one (identified as “A” on the slide) refers to motion environments with vibration crest factor is less than 9 (the crest factor defined as the magnitude of the ratio of the peak value of the frequency-weighted acceleration signal to its RMS value), or for environments not containing occasional shocks of transient vibration. The second one (identified as “B” on slide) refers to motion environments where the vibration crest factor is above 9 (or 6 according to BS 6841:1987), or for environments containing occasional shocks of transient vibration. For motion environments “A” the frequency-weighted RMS acceleration should be used, whereas for environments “B” either the running RMS method, or the fourth power vibration dose method (VDV) should be used. VDI 2057 Part 1 proposes the running RMS acceleration method but with an alternative approach.The fourth power vibration dose method (VDV) is more sensitive to peaks because of the implementation of the fourth power instead of the second, and as noted by BS 6841:1987 the method is not limited to crest factor considerations.Distinguishing which method to use depends on the motion envelopes, and therefore on the characteristics of the anticipated motion. The two concept maps depicted on the slide show how ISO 2631-1 and BS 6841 approach this issue. Although different methods are proposed for the two environments, it should be noted that BS 6841:1987 reports that “in all cases the RMS frequency weighted acceleration should be determined”, and ISO 2631-1:1997 that “in all cases where one the additional methods is also used, both the basic evaluation method [i.e. frequency-weighted RMS acceleration] and the additional evaluation value shall be reported”.
• #13: The basic method used for assessing motion sickness is the energy-equivalent motion sickness dose value (MSDV), which is based on the evaluation of frequency weighted root mean square (RMS) acceleration. The z-axis RMS acceleration is evaluated at frequencies between 0.1 Hz and 0.5 Hz, and then is multiplied by the frequency weighting coefficient. The value (in meters per second to the 1.5 power) is given by two alternative methods based on frequency weighted acceleration in the z direction. If motion can be determined from motion measurements throughout the full period of exposure, is given by the first equation, where T is the total period (in seconds) during which motion could occur. On the other hand, if motion is continuous and of approximately constant magnitude, MSDV value can be estimated from the frequency weighted determined over a short period of time . In this case, equation 2.Then, we can evaluate the percentage of persons who may vomit based on MSDV value multiplied by a factor Km. This constant equals to one third for a mixed population of males and females.The percentage of persons who may vomit is a metric introduced during the HFR experiments as a convenient metric to evaluate motion sickness severity. The term coined was motion sickness incidence (MSI) and as ISO 5805:1997 clearly defines it “motion sickness incidence is the fraction (usually expressed as a percentage) of a group or population who succumb to motion sickness (usually defined as frank emesis) within a specified period or in specified conditions of provocative motion”. From the eight standards referring to motion sickness, 3 identified a limiting criterion.The motion criterion set by ABS 103 for 30 m/s^1.5 (MSDVz) aims at restricting the passengers who may vomit to less than or equal to 10% (without referring to the dimension of time). The same criterion is used in ASTM F1166-07 (<=10% MSI for personnel), where it is noted that this applies to “limited duration exposures” without accounting for adaptation issues occurring at longer exposures. On the other hand, STANAG 4154 identifies criteria for MSI based on specific missions. For Transit and Patrol, and Replenishment at Sea (CONREP, FAS, and VERTREP) it recommends MSI 20% of the crew at 4 hours period. Finally, MIL-STD-1472F does not propose any definite criterion. Instead it notes that “The weighted RMS acceleration in the z-axis (between 0.1 and 0.5 Hz) should be sufficiently low to preclude or minimize motion sickness”.At this point a note should be made for the withdrawn ISO 2631-3:1985. This standard included the criterion of 10% MSI for a 4-hour period. Nevertheless, as also noted later in STANAG 4154, the motion limit contours included in that standard were based on “severe discomfort associated with MSI…”. In general, it is unclear on what basis these standards propose the guidance depicted on the slide. Whereas, it is obvious that criteria referring to passengers are based on the impact of motion sickness to subjective evaluation of comfort, it should be different for crew personnel for whom performance is related to the effects on their tasks.
• #14: Given what we already mentioned about the discussion of motion sickness, it is interesting to observe what information is depicted in the eight standards.
• #15: Comfort is a term often fuzzy in its definition. Aiming at civilian passengers, ABS 103 defines it as “the acceptability of the conditions of a vessel as determined by its vibration, noise, thermal, indoor climate and lighting qualities as well as its physical and spatial characteristics, according to prevailing research and standards for human comfort”, whereas ABS 102 defines comfort (aiming to crew) as “the ability of the crew to use a space for its intended purpose with minimal interference or annoyance from vibration”. In general comfort is a subjective evaluation of one’s self-state dependent at large in the person’s mood, activities involved (whether you are involved in working, training, trying to sleep, etc), and the ambient situation (for example environmental conditions combined on personal expectations).Comfort is addressed by nine of the 14 “core” publications. ABS 102 and 103 refer to BS 6841, whereas the rest refer to ISO 2631-1:1997.CriteriaThe two basic standards, ISO 2631-1:1997 and BS 6841:1987, do not provide any criteria, but they indicate some comfort reactions based on frequency-weighted RMS accelerations as depicted on Table 1.MIL-STD-1472F refers to these comfort indications and notes they should not be exceeded. Furthermore, BS 6841:1987 notes that vibration magnitudes and durations which produce vibration dose values in the region of 15 will usually cause severe discomfort.Given that ABS 102 proposes two levels of habitability notation, HAB notation aims at preventing crew severe discomfort, whereas HAB+ aims at improving crew comfort. For HAB the standard proposes 0.4 RMS m/s^2 acceleration, whereas for HAB+ it proposes 0.315 m/s^2 RMS acceleration. ABS 103, aiming at passengers, proposes COMF notation, and COMF+ notation for optimal passenger comfort. For COMF the standard proposes 0.315 m/s^2 RMS acceleration, whereas for COMF+ it proposes 0.20 m/s^2 RMS acceleration.ASTM F1166-07 proposes the limit (already mentioned in ISO 2631-1:1997 and BS 6841:1987) of 0.315 RMS acceleration for operational environments with limited or continuous whole-body vibration without the existence of occasional or repeated shocks (Type III and IV environments).As it is depicted on Table 2, ISO 6954:2000, which refers to habitability on passenger and merchant ships, identifies RMS acceleration criteria for three areas onboard a ship based on whether adverse comments are probable or not probable
• #16: The vibration envelope induced to human onboard ships may include high intensity vibration of short duration (shocks or impacts) to low intensity vibration of very increased duration (life span). Accordingly, the health effects of whole body vibration span over a wide range of symptoms ranging from just noticeable perception of motion to death. The dimension of time in vibration exposure may lead to chronic effects (injuries), even though the levels of vibration are not adequate to provoke acute effects (Dupuis & Zerlett, 1986; Griffin, 1990). Existing results from epidemiological studies identify that long term whole-body vibration is associated to health effects including injury or musculoskeletal disorders like herniated lumbar disc, low back pain, or sciatic pain (Bernard, 1997; Bovenzi & Hulshof, 1998; Wilder, 1993). Nevertheless, as noted by BS 6841:1987 “Epidemiological studies suggest that back complaints are associated with exposure to prolonged periods of vibration and repeated shock but there are currently inadequate data to define a precise dose-effect relationship. Similarly, it is not yet possible to provide a definitive dose-effect relationship between whole-body vibration and any other injury”.Eight standards include information regarding health related effects of motion (ASTM F1166-07, BS 6841:1987, BS 14253, ISO 2631-1, ISO 2631-5, MIL-STD-1472F, 2002/44/EC, and VDI 2057 Part 1).ISO 2631-1:1997 guidance is based on a) seated persons’ research, and b) the assumption that responses are related o energy. Furthermore, it is recommended for exposures in the range of 4 to 8 hours, as depicted on Figure 1. The shaded area is the health guidance zone where caution to potential health risks is indicated, whereas above this zone health risks are likely.Obviously, the aforementioned are affected by the frequency weighted RMS acceleration method considerations and constraints already mentioned. Therefore, when crest factor is more than 9, or the other indications apply (for the occurrence of shocks or transient effects in general), then the VDV methods should be used instead.MIL-STD-1472F also proposes that frequency-weighted RMS translational accelerations should not exceed the health guidance caution zones for the expected daily exposures. Furthermore, it notes that exposures within the health guidance caution zone should be avoided, whereas frequencies below 20 Hz should be avoided and/or minimized.On the other hand, ISO 2631-5:1997 tries to fill in the gap in appropriate methodology regarding the assessment of health effect when shocks and transient phenomena are evident. The limits proposed in this standard for the assessment of adverse vibration effects, are based on a 240-day annual exposure at a) N years of exposure, or b) for lifetime exposure.ASTM 1166-07 takes a slightly different approach by grouping the provided limits according to the type of the operational environment. For Type I environments (motion environment containing some underlying vibration, but it is predominantly characterized by repeated shocks or transient vibrations; exposure can be of any duration) guidance is based on equivalent static compressive stress value Sed. At these environments, when impact accelerations do not exceed 4 Gs, should be less than 0.5 MPa (for low probability of adverse health effects at a lifetime exposure). If exceeds 0.8 MPa then there is high probability. If impacts routinely exceed 4 Gs and there is only a military population, then the corresponding limits become 3.9 MPa and 4.7 MPa, respectively ( Sed values normalized over an 8-hour period). For Type II environments (motion environment characterized as predominantly sinusoidal in nature, where occasional shocks or transient vibrations are present; exposure can be of any duration) analysis depends on the crest factor. If it exceeds 9.0, then the RMS vibration levels shall not fall within the “health risks are likely” zone, and should preferably fall into the “minimal risk to health” zone of Figure 2.If the crest factor exceeds 9.0, then the daily exposure should not exceed the limit proposed by Directive 2002/44/EC.For Type III environments (characterized as predominantly sinusoidal, with no shocks or transient vibrations; exposure limited to less than eight hours) the RMS vibration levels shall not fall within the “health risks are likely” zone, and should preferably fall into the “minimal risk to health” zone of the previous figure. Finally, for Type IV environments (characterized as predominantly sinusoidal, with no shocks or transient vibrations; continuous exposure greater than eight hours) the RMS vibration levels shall not exceed 0.4 , and should preferably be less than 0.315 .
• #17: Four standards (ABS 102, BS 6841:1987, MIL-STD-1472F, NATO STANAG 4154:ed. 3) and one publication of interest (Graham, 1990) include information regarding the effects of ship’s motion on human activities including motion induced interruptions. The general method for evaluating these effects is the frequency weighted RMS acceleration. When referring to human activities current standards address an extended range of biodynamic interferences including hand (or finger) manipulation and control, vision, and incidents of stumbling because of sliding or losing balance (Motion Induced Interruptions - MIIs). ABS 102, which refers to BS 6841:1987, focuses on the interference of ship motion with work tasks of standing crew members’ performance (without any further detailed information on the term “work tasks”). BS 6841:1987 addresses the effects of vibration (coordinated control of hand movements and vision) transmitted to the seated body, primarily for environments with low crest factor motions, whereas MIL-STD-1472F addresses major body resonances and the impairment of visual tasks. The guidance proposed by the aforementioned standards is mainly based on RMS acceleration criteria. In ABS 102, HAB habitability notation aims at motion interference, and the guidance provided is of 0.4 m/s2 maximum weighted RMS acceleration. For hand or finger control with accuracy of within 5 mm RMS, or for visual detail which subtends less than 2 minutes of arc at the eye, BS 6841 proposes that the weighted acceleration magnitude should not exceed 0.5 m/s2.  MIL-STD-1472F uses a different approach. Without proposing specific criteria, it notes that frequencies below 20 Hz should be minimized because major body resonances occur at this region, and it further proposes that frequencies between 20 and 70 Hz should be minimized to preclude impairment of visual tasks (DoD, 1999). The latter region of frequencies above 20 Hz is further emphasized when “visual performance is critical.” Finally, STANAG 4154 identifies two sets of criteria associated with human performance limitations, the recommended and the default. The latter are expressed in weighted RMS accelerations, whereas the recommended are based on the MSI model, and on the expected MIIs model (Graham, 1990). Tables on the slide depict these criteria. STANAG 4154:Ed. 3 proposes these criteria for Transit and Patrol (TAP) missions. Specifically, the 1MII/minute criterion is applicable to: a) ordnance handling, arming and maintenance (weapon and sensor systems during TAP and Naval Air Operations – NAO), and b) for maintenance and repair. The more conservative 0.5 MIIs/minute criterion is proposed for Replenishment at Sea, Anti-submarine Warfare missions (towed array launch), and Weapon Systems Reload (chaff, CIWS, support equipment), The last comment in this section must include the significant work by Graham (1990) on Motion Induced Interruptions (MIIs) indicating sliding and tipping during ship deck operations. Although this work is cited in STANAG 4154, it is useful to note that it proposes a taxonomy of derived limiting criteria based on the unit of the number of MIIs per minute. These criteria, depicted on Table 2, are reported as “preliminary values” for further evaluation and accurate definition with future operational studies.
• #18: The term “Manual material handling” in current standards refers to lifting, carrying, or pushing/pulling a weight.MIL-STD1472F and ASTM F1166-07 generally propose identical limits, although a) ASTM F1166-07 is more detailed, includes more carrying tasks, and refers to a population including from the 5th female to the 95% male, and b) MIL-STD1472F includes guidance for male/female or male only population.  The information included hereafter is only a brief extract of the guidance involved in the aforementioned standards. For one person lifting an object with uniform mass distribution and a compact (46 cm high and wide, 30 cm deep), or carrying, the following apply:These limits may be doubled when two persons are conducting the tasks. For the third and each additional operator, not more than 75% of their capability should be added. If frequency of lifts exceeds one per five minutes or 20 lifts per eight hours the weight limits should be reduced by %, where is the lift frequency in lifts per minute.  For pushing and pulling tasks (where the male population is involved) the following guidance applies (Table 4)These limits may be doubled for two persons or tripled for three persons conducting the tasks simultaneously. For the fourth and each additional operator, not more than 75% of their capability should be added.It is interesting to observe, though, that the guidance provided by both the aforementioned standards does not include the effect on motion on the proposed limits. Therefore, they should be regarded as static given that they refer to a stationary environment.
• #19: The last standard addressing MMH issues extends its scope beyond the generic tasks of lifting, carrying, or pushing/pulling a weight. NATO STANAG 4154:ed 3 focuses on complex manual tasks related to material and equipment handling often conducted on naval ships.These tasks may include manual missile or torpedo handling, moving a helicopter, handling of ammunition etc.The related criteria are given as roll and pitch RMS amplitude in degrees. The depicted Table shows the proposed guidance vs the type of mission (Transit and Patrol - TAP, Naval Air Operations – NAO) or specific operation they refer to (Weapon Systems Reload – WRL).
• #20: Review of existing standards showed that although the definition of sopite syndrome exists in ISO 5085:1997 (“inordinate sleepiness, lassitude or drowsy inattention induced by vibration, low-frequency oscillatory motion (e.g. ship motion) or general travel stress”..), none of them provided guidance or limiting criteria. The only reference found was a comment in VDI 2057 Part 1 addressing the symptoms of sopite syndrome, when noting that “whole-body vibration with frequencies less than 1 Hz are a frequent cause of drowsiness and a reduced activation level”, but no other, related, information is given (VDI, 2002).
• #21: Generally, sleep loss is expected to lead to the following negative effects:  Lack of concentrationLapses of attentionReduced vigilanceSlowing of actionImpaired short-term memoryDifficulty in comprehensionMisinterpretationDisorientation.A summary regarding the major effects of sleep loss relevant to designers is reported in DEF STAN 00-250 Part 3 Section 9 (MoD, 2008c), where it is noted that “[the] tasks most affected by sleep loss include those that are complex, uninteresting, lengthy, require sustained attention, subsidiary, work-paced, entail a long memory chain, or demand protracted viewing periods at short range. Tasks least affected by sleep loss include those that are short, simple, interesting, self-paced, or physical”.Albeit the significant volume of research regarding the effect of sleep on human performance, very little is known about the relation between induced whole body motion while asleep and sleep quality or quantity. [Warhurst and Cerasani (1969) noted subjective reports of sleep disturbance due to heavy roll during a 2-week cruise onboard a USS GLOVER (AGDE-1), a 3400 tons destroyer. Later, a survey of the effects ship motions on fatigue, identified the severity of issues regarding sleep quality and duration, with consecutive effect on mental and physical fatigue (Colwell, 2000a, 2000b). Finally, sleep disturbance problems were reported in a survey of personnel involved in offshore operations (Cheung, Brooks, & Hofer, 2002)].This gap is consequently identified in existing standards, where deterioration of sleep due to platform motion is not approached, although a few sporadic comments do exist (HSE, 2001).
• #22: None of the reviewed standards addressed MIF. Only STANAG 4154 notes that no methods exist to evaluate motion effect to fatigue (NATO, 2000).
• #23: ABS Doc. No. 102: 2001 - Title: Guide for Crew Habitability of ShipsABS Doc. No. 103: 2001 - Title: Guide for Passenger Comfort on ShipsASTM F1166-07: 2007 - Title: Standard Practice for Human Engineering Design for Marine Systems, Equipment, and Facilities - Section 14.4: Whole-body vibration and shockBS 6841: 1987 - Title: Guide to Measurement and Evaluation of Human Exposure to Whole-Body Mechanical Vibration and Repeated ShockBS 14253:2003 - Title: Mechanical vibration. Measurement and evaluation of occupational exposure to whole-body vibration with reference to health. Practical guidanceISO 2631-1:1997 - Title: Mechanical vibration and shock - Evaluation of human exposure to whole-body vibration - Part 1: General RequirementsISO 2631-4: 2001Title: Mechanical vibration and shock -- Evaluation of human exposure to whole-body vibration -- Part 4: Guidelines for the evaluation of the effects of vibration and rotational motion on passenger and crew comfort in fixed-guideway transport systemsISO 2631-5: 2004 - Title: Mechanical vibration and shock - Evaluation of human exposure to whole-body vibration - Part 5: Method for evaluation of vibration containing multiple shocksISO 6954: 2000 - Title: Mechanical vibration - Guidelines for the measurement, reporting and evaluation of vibration with regard to habitability on passenger and merchant shipsMIL STD 1472F: 1999 - Title: Design Criteria Standard on Human EngineeringSTANAG 4154:2000 - Title: Common Procedures for seakeeping in the ship design processVDI 2057 part 1 (VDI 2057 blatt 1): 2002 - Title: Human exposure to mechanical vibrations - Whole-body vibrationPublisher: VDI-GesellschaftEntwicklungKonstruktionVertrieb2002/44/EC Directive of the European Parliament and Council - Title: The minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (vibration)Graham:1990 - Title: Motion-Induced Interruptions as Ship Operability CriteriaNORDFORSK:1987 - Seakeeping performance of ships