first intact stability code, beginning of development of 2nd generation intact stability criteria, present status and the Keywords: Ship stability, 2nd generation stability criteria, ship safety. 1. .. explanatory notes to the IS Code have. To this end, the Committee approved the Explanatory Notes to the Intact Stability. Code, , set out in the annex, as prepared by the. caite.infon - Ebook download as PDF File . pdf), The IS Code (resolution MSC. to minimize the risk to such ships.

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"the Load Lines Protocol"), respectively, to make the introduction and the provisions of part A of the International Code on Intact Stability, mandatory. The revised and renamed Intact Stability Code (IS Code). The IS Code consists of two different parts: Part A which include the mandatory Download PDF. PDF | SUMMARY Provisions concerning intact ship stability have been introduced at The revision of the Intact Stability Code, IMO Res. .. introduced the new generation intact stability criteria in (Francescutto, ).

The modes of operation of a unit include the following: The upper part of ; 9 Hashimoto, et al. They may also be applied to other cargo ships in this length range with considerable flare or large water plane areas. An important point is that there was one half of the 1 curve roll cycle associated with the passing of an entire wave. Christopher Bassler. As surf-riding is in most cases a stationary condition, the Difference between wave profile does not vary relative to the ship.

Because oscillations grow inside the instability zone and decay outside the instability zone, the solution has to be The application of the criterion for parametric roll in periodic at the boundary.

To account for the damping already Equation 27 obviously requires more computational work than included in Equation 13 , it is enough to satisfy: Vulnerability Criteria, are presented in Tables 3 and 4. As a result of using coefficient q that is related to the magnitude of parametric this conservative assumption, only the tanker was found not excitation 9 and coefficient p, the ratio of the natural vulnerable.

Application of the approximation given in Equation length. Since the frequency of encounter depends on speed, 24 for the magnitude of the parametric excitation provides Equation 25 can be used to determine whether if the design results that are similar in terms of resolution. All the container carriers and the cruise vessel are found to be susceptible to A more sophisticated criterion can be proposed if actual parametric roll, while tugs, tankers and bulk carriers are not.

To account for the Generally, this is consistent with existing operational likelihood of encountering different waves, a series of wave experience.

Results criterion is similar to: Once the amplitude of the roll oscilla- the onset of parametric roll. However, it is not capable of tion becomes large enough, the frequency condition for parame- estimating the amplitude of parametric roll; once parametric tric resonance is no longer satisfied, as the change in instan- resonance in a linear system has started, its amplitude grows taneous GM leads to a change in the instantaneous natural fre- without any limit.

Nonlinearity stabilizes parametric resonance quency. It is a well-known phenomenon of nonlinear roll—the at certain amplitude see Figure This means that once a cer- 60 tain roll amplitude has been exceeded, further flow of energy Mathieu linear periodically changed GZ equation curve into the dynamical system stops.

Figure These considera- Its mechanism is slightly different from one with the GZ curve. The increase in roll rate makes nonlinear damping large approximation: Also, if the roll amplitude is large enough, damping becomes dependent on the roll angle. The edge submerges into the water. As mentioned above, the calculation of the instantaneous While this method for evaluating the heave and pitch GZ curve in regular waves is straightforward.

However, the attitude for stability in waves seems to be the most physically assumption of low-encounter frequency is not always applicable sound, several assumptions must be made regarding the heave for parametric roll as it was for pure loss of stability, since the and pitch hydrodynamic coefficients.

If a seakeeping analysis former may occur in head and bow-quartering seas as well as in has been performed at this stage in the design process, the added following and stern-quartering seas. If the vulnerability to The attitude of a ship is calculated based on the heave and parametric roll needs to be addressed earlier in the design process, additional assumptions are inevitable. It is quite simple to test these where M is mass of the ship; IY is the mass moment of inertia assumptions by direct comparison between the results of the relative to the transverse axes; A33 and A55 are heave-added mass simplified calculations and complete potential flow solutions.

FH Once the attitude of the ship for each wave crest position and MH are hydrodynamic components of the wave excitation. These values are expressed as follows: It is a nonlinear ordinary, differential equation and center of buoyancy in calm water. Both calculate an area and a static moment relative to the y-axis of a options allow consideration of nonlinear damping along with station located at a longitudinal position along the hull, x. The nonlinear restoring.

For example, the restoring function is considered in the following form: Runge-Kutta solver. Then, the following algebraic equation can be obtained for Equation 33 reduces to Equation It can be shown that Equation 31 yields a linear solution Sample calculations using a direct numerical solution are if: These results are of a preliminary Substitution of the above expressions in Equation 32 into nature as the procedure for calculations has not yet been Equation 31 reduces the latter to: The initial roll rate was zero in both cases.

Then, the consistent with the level 1 criterion in Equation In a case of no parametric resonance, roll motions vessels. While the issue of the allowable roll angle needs will decay and the maximum roll angle will be the initial angle.

Quick development of parametric roll is observed An important observation is that the result of sample for container carriers, RoPax and cruise vessels; and these calculations for level 2 vulnerability criteria is, in general, less results are consistent with existing experience. While the two sample fishing vulnerable by the level 1 criteria have been found non- vessels in the above table did not indicate any vulnerability to vulnerable by the level 2 as well. Neves, et al. Some differences in the Physical Background of Surf-riding and Broaching-To severity of the parametric roll response were observed in case of Broaching-to is a violent uncontrollable turn, which occurs MPVs, depending on their loading conditions see Table 6.

As with any other sharp-turn The question remains about what roll angle should be used event, broaching-to is accompanied with a large heel angle, as a standard. The ABS Guide used Broaching-to value came from a limit on the main engine operability for is mostly associated with operating in following and stern- container carriers. It is based on lubrication requirements at quartering seas.

Stability failure caused by broaching-to is static inclinations. Another standard might be proposed based known as a problem mainly for fishing vessels and high-speed, on container-lashing requirements; this seems to be logical, but monohull passenger ships. Broaching-to is often preceded by surf-riding. Surf-riding leading backwards and away from the wave crest.

To the outside observer, surf-riding looks like a that lead to surf-riding; the rest of the phase plane corresponds transition from periodic surging when waves overtake a ship to to surging. This transition is a well-known and established nonlinear phenomenon that has been discussed several times in the F, kN literature e. Grim, ; Kan, From a nonlinear Positions on the dynamics perspective, the fundamental dynamic sequence that wave leads to surf-riding and then to broaching-to has been identified by Spyrou , As surf-riding is in most cases a stationary condition, the Difference between wave profile does not vary relative to the ship.

Furthermore, thrust and resistance during surf-riding some ships exhibit dynamic yaw instability, Unstable despite active control. This leads to the uncontrollable turn Equilibriu Stable Wave surge force identified as broaching-to. Therefore, the likelihood of surf- m Equilibriu riding could be used in order to formulate suitable vulnerability m criteria for broaching-to. For surf-riding to occur, the wave Figure Surf-Riding Equilibria for a m High-speed length is usually comparable with the ship length.

Large ships Vessel, Wave Height 6 m, Wave length m, Speed cannot surf-ride because waves of the necessary length are Setting 24 kn simply too fast compared to the ship speed. As can be seen from Figure 14, there are two crossings and, therefore, two equilibria on the span of one wave. One of these equilibria is located near the wave crest. It is 10 unstable in surge in that if a ship is perturbed from this position, Surf-riding Surf-riding it will continue the motion rather than returning to the equilibrium position.

Surging Surging There are two characteristic speed settings or nominal 10 Froude numbers, associated with surf-riding. One is called the critical speed for surf-riding under certain initial conditions or Figure Phase Plane with Surging and Surf-Riding Belenky, the first critical speed, or the first threshold , and the other is et al. The critical speed for surf-riding under certain initial Surging and surf-riding do not coexist for all speeds. The speed surf-riding equilibria exist which is shown in the phase plane or nominal Froude number corresponding to that situation is diagram Figure These two Froude numbers effects may be important for some ships Sadat-Hosseini, et al.

Wave capture associated with surf-riding is not just an Once the amplitude for the wave-surging force is acceleration phenomena, in fact if wave capture occurs while calculated, the first threshold can be found by solving the going faster that the wave celerity, deceleration will occur. Thus, a criterion derived from Equation 37 would unnecessarily penalize ships.

To understand this, the simplest mathematical model describing surf-riding and surging Figure 16 Changes of the Phase Plane with Increase of Speed can be considered: This force is a result of the integration of the incident initial conditions: The initial conditions can be plotted on a graph: Another way to determine the threshold is by detecting the and x, y and z are the coordinates of points on the surface of the change of the shape of the boundary between the domains of hull, expressed in a ship-fixed coordinate system; y x, z is the surf-riding and surging.

While effects of nonlinear incident waves are rather unstable equilibria, respectively see also Figure The limited, even in steeper waves; three-dimensional diffraction boundary between surging and surf-riding can be found by integration starting from an unstable equilibrium.

The idea is based on the fact that the boundaries overlap danger of broaching. First introduced in by MSC.

Therefore, the The analysis resulted in the following formula: Practically, this means that the waves. In contrast yields: One can also relax the requirement of low damping, g but this would be at the expense of not obtaining a closed form Taking advantage of the experience with the application of solution. Thus, ships with service speeds transformed into the following non-dimensional form: This wave steepness is quite high and the likelihood of encountering a long and steep wave is less than the likelihood of encountering a short and steep wave.

Despite the fact that the process of when its length is less than m. The vulnerabil- Spyrou, combines the probabilistic nature of realistic ity to surf-riding can be measured by the percentage of waves waves and a deterministic description of ship dynamics.

Umeda capable of generating surf-riding. First, lengths and amplitudes and the statistical weight of each wave is combinations of wave height and wave length leading to calculated using Equation 3. The results can be regarded as dangerous broaching-to were determined by numerical the probability of occurrence of surf-riding when a ship meets a simulations in regular waves. Then, the probability of wave with the assumed wave length and amplitude. Finally, the method or a numerical method using the phase plane was probability of broaching-to was estimated as the probability of considered too complex for the level 1 vulnerability criterion.

The simultaneous increase of the wave length and requirements for level 2. Similar conclusions were reached by Peters, et al. Only two ships This comparison using Froude number, Fn yields a factor C2ij: Ship Description m kn Fn 0. Bulk Carrier DWT 14 0. C2 C2L 0. Bulk Carrier 16 0. The of wave numbers and amplitudes used for calculation of results are also consistent with the level 1 vulnerability criterion. The where P HS,TZ is the statistical frequency of observation of a objective of the direct stability assessment is two-fold: The data for averaging between different the development of ship-specific operational guidance.

IACS The simulations use potential flow Table 8 contains the results of calculations carried out on a wave-body hydrodynamic methods, and are supplemented by sample population of ships. Assuming a standard of 0. This prediction is be computed efficiently and accurately.

As a result, there is no generally consistent with operational experience. The need for the separation of restoring and exciting forces; strictly differences between short-term and long-term criteria seem to be speaking, that can be done only under assumptions of linearity. Keeping in mind that both pure loss of stability and parametric Addressing the problem of rarity requires application of special roll are largely driven by hydrostatic and Froude-Krylov forces, extrapolation procedures.

Each mode of failure may require a the fidelity of their modeling requires a serious consideration. The hull forces in maneuvering Committee focused on new criteria that would address the depend on vortex phenomena and cannot be easily modeled dynamic stability failures not yet covered, including pure loss of using potential flow assumptions. Inclusion of empirically- stability, parametric roll, and broaching-to. These errors is based on a multi-tiered evaluation process.

Because the direct are partially caused by double counting for wave forces that are stability assessment of ship-stability performance may incur implicitly included in the empirical data and inherently substantial additional design analysis expense, a vulnerability calculated by the potential code.

Despite these difficulties, there check needs to be performed first, to exclude cases where the has been substantial progress in the development of modes of stability failure are not a concern. Vulnerability checks hydrodynamic models for maneuvering in waves cf. Yen, et al. Meanwhile, the modeling of ship maneuvering by a unnecessary conservatism. Validation remains an important problem for all tools that The level 1 vulnerability criteria for pure loss of stability is might be used in a regulatory framework Reed, The results may influence the application of these codes in a level 2 vulnerability check is performed with the GZ curve regulatory framework.

The answer may be different for changing in waves, using different parameters as the criteria. However, this issue remains For parametric roll, the level 1 vulnerability criteria is based outside the scope of this paper.

Two conditions are used: The level 2 vulnerability criterion is practical application in direct stability assessment. There must based on the roll response under conditions of parametric be a process for applying the tool that leads to a conclusion resonance. The vulnerability criteria for broaching-to focuses on surf- The framework of the second generation intact stability riding, as the latter is usually a pre-requisite for broaching-to.

If the safety level is service speed in terms of Froude number and vessel length. The expressed in the form of a long-term probability of a particular level 2 criterion is based on the threshold speed for surf-riding mode of failure, it creates a basis for comparison and a under any initial conditions. The The next objective in the development of the second importance of establishing good safety level criteria is that the generation intact stability criteria is defining the requirements level of safety of a new ship design can be judged against the and procedures necessary for direct assessment.

This is a safety level of an existing ship with a long history of safe formidable task. Not only must the most advanced technologies operation.

A short-term probability of failure is evaluated under to be the most appropriate tools for predicting pure loss of the assumption that the environment can be described as a stability and parametric roll.

Broaching-to is best modeled with stationary stochastic process. However, calculation of this a system of ordinary differential equations until more advanced probability represents a significant challenge because a stability hydrodynamic codes gain enough maturity for this application.

Thus, the estimate of the Development of validation procedures for time-domain probability of failure by direct counting is impractical.

The simulation tools is another difficult, but absolutely necessary calculation of short-term probability of ship stability failure is task. This means that stability failures ABS Guide for the Assessment of Parametric Roll Reso- must be regarded as random events and, since they are rare, the nance in the Design of Container Carriers, American Bu- problem of rarity needs to be addressed with a set of appropriate reau of Shipping, Houston, TX, 70 p. Belenky, G.

Bulian, A. Francescutto, K. Spyrou, N. Also, an additional mode of intact stability failure, Proc. Petersburg, Russia, pp. Miller, A. Brown Once the criteria development is complete, two more stages Considerations for Bilge Keel Force Models in Potential will be needed. While this problem has been tackled in other fields of engineering, it has not yet been adequately addressed as far as BECK, R. Reed Modern computational intact stability is concerned.

SNAME, Influ- on exiting and future fleets.

Naval Engineers J. Marine Tech. Sevastianov Stability and The views and opinions expressed in this paper are solely and Safety of Ships: Risk of Capsizing 2nd ed. Nonlinear the Nippon Foundation. The authors express their sincere Analysis: Real World Applications, 5: Art Reed and Ms.

Trieste, Trieste, Italy. Francescutto A simplified regulatory- improved clarity and readability of the text. IMO Res. Brouwer, K. Intact Ship Survivability in Extreme Waves: New in Length, London, UK, 15 p.

Criteria from Research and Navy Perspective. Stability of over, London, UK, 5 p. Levadou, T. Treakle, J. Paulling, K. Moore Developments and Trends. Reederei-Hafen, Jahr- London, UK, 65 p. Marine Sci.

London, UK, 2 p. Submitted by the Royal Institu- Rev. Umeda, eds. London, UK, 19 p. Krylov Soc. Submitted by Italy, London, 4p.

Head Seas. Mook A theoretical and London, UK, p. Royal Soc. Ship Res. Schaffran Experi- mental studies of capsizing of intact ships in heavy seas.

Also IMO Doc. Wood Ship motions and capsizing in astern seas. The alternative stability criteria contained in 2.

Relaxations from the requirements of the Code may be permitted by an Administration for vessels engaged in near-coastal voyages off its own coasts provided the operating conditions are. The disposition of the freeing ports should be carefully considered to ensure the most effective drainage of water trapped in pipe deck cargoes or in recesses at the after end of the forecastle. Access to spaces below the exposed cargo deck should preferably be from a position within or above the superstructure deck.

Any access to the machinery space from the exposed cargo deck should be provided with two weathertight closures. In vessels operating in areas where icing is likely to occur. The Administration may also apply these provisions as far as reasonable and practicable to special purpose ships of less than gross tonnage. The righting moment curves and wind heeling moment curves should be related to the most critical axes.

Account should be taken of the free surface of liquids in tanks. For MODUs constructed before that date. Righting moment and wind heeling moment curves Any such unit should. Clustered deck-houses or similar structures c. Values of the coefficient C. F where: F is the wind force N member exposed to the wind see table 2. Shape Spherical Cylindrical Large flat surface hull. Recommended design criteria for certain types of ships Table 2. Righting moment and heeling moment curves Such heeling moment determination should include lift and drag effects at various applicable heel angles.

For ship-shaped hulls the curve may be assumed to vary as the cosine function of ship heel. The unit is to be assumed floating free of mooring restraint. The procedures recommended and the approximate length of time required. It should be possible to achieve the severe storm condition without the removal or relocation of solid consumables or other variable load.

Any wind and wave spectra used should cover sufficient frequency ranges to ensure that critical motion responses are obtained. Analysis should include the results of wind-tunnel tests. In determining the acceptability of such criteria. GM cannot be taken to be greater than 2. Righting moment and heeling moment curves 2. The initial down-flooding distance DFDo should be greater than the reduction in down-flooding distance at the survival draught as shown in figure 2.

GM is the metacentric height measured about the roll or diagonal axis. Definition The parameters graph 2. This axis is usually the diagonal axis as it possesses a characteristically larger projected wind area which influences the three characteristic angles mentioned above m.

Vc Vp V GM is the metacentric height measured about the axis which gives the minimum downflooding distance margin i VCPw1 Recommended GM design criteria for certain types of ships for paragraph International Code on Intact Stability.. In doing so. Except as permitted in 3. Free surface effects for small tanks may be ignored under the condition specified in 3. The free surface correction should be defined for the actual filling level to be used in each tank.

Free surface effects need not be considered where a tank is nominally full. Guidance in preparing stability information 3. Permanent ballast particulars should be noted in the ship's stability booklet.

Permanent ballast should not be removed from the ship or relocated within the ship without the approval of the Administration. The loading conditions which should be considered for ships carrying timber deck cargoes are specified in 3. This percentage should be 30 if the freeboard amidships is equal to or less than 0. The net volume should be taken as the internal volume of the pipes.

Its quantity and disposition should be stated. In the arrival condition. The calculations should take into account the volume to the upper surface of the deck sheathing.

In assessingthe quantity of trapped water. As guidance. In the presence of port-starboard asymmetry. IMO guidance for testing these windows is to be developed.

B In cases where the ship would sink due to flooding through any openings. Guidance in preparing stability information sidered without deadlights in additional tiers above the second tier. All translations of the stability booklet should be approved. Comprehensive rolling period tables or diagrams have proved to be very useful aids in verifying the actual stability conditions. On a mobile offshore drilling unit.

This Code addresses only the stabilityrelated contents of the booklet. Hatchways may also be taken into account. The stability booklet may include information on longitudinal strength. Such information should enable the master. The Administration may have additional requirements.

Guidance in preparing stability information. In developing the stability booklet. The master should: It should be calculated having regard to: The masters of ships having a length less than m should also: This recommendation may not apply to all ships and the master should take into consideration the stability information obtained from the ship's stability booklet.

Ballasting and deballasting should be carried out in accordance with the guidance provided in the Code of Safe Practice for Ships Carrying Timber Deck Cargoes. Refer to the Guidance on intact stability of existing tankers during liquid transfer operations MSCjCirc. A stability instrument installed on board should cover all stability requirements applicable to the ship. The software is subject to approval by the Administration. Active and passive systems are defined in 4.

These requirements cover passive systems and the off-line operation mode of active systems only. A translation into a language considered appropriate may be required. The software should be modified accordingly and re-approved. Three types of calculations performed by stability software are acceptable depending upon a vessel's stability requirements: Type 1 Software calculating intact stability only for vessels not required to meet a damage stability criterion. Type 2 Software calculating intact stability and checking damage stability on basis of a limit curve e.

Type 3 Software calculating intact stability and damage stability by direct application of pre-programmed damage cases for each loading condition for some tankers, etc. The results of the direct calculations performed by the stability instrumentcould be accepted by the Administration even if they differ from the required minimum GM or maximum VCG stated in the approved stability booklet.

Such deviations could be accepted under the condition that all relevant stability requirements will be complied with by the results of the direct calculations. The following parameters should be presented for a given loading condition:. GM and GML. The accuracy of the results should be determined using an independent program or the approved stability booklet with identical input.

Deviation from these tolerances should not be accepted unless the Administration considers that there is a satisfactory explanation for the difference and that there will be no adverse effect on the safety of the ship.

For ships carrying liquids in bulk. For ships carrying grain in bulk. The satisfactory operation of the stability instrument is to be verified by testing upon installation refer to 4.

The test conditions normally should cover the range of load draughts from the deepest envisaged loaded condition to the light ballast condition and should include at least one departure and one arrival condition. A copy of the approved test conditions and the operation manual for the stability instrument are to be available on board. Within the test conditions each compartment should be loaded at least once. Main dimensions. Stability calculations performed by stability instruments 4. From the approved test conditions at least one load case other than lightship should be calculated.

Actual loading condition results are not suitable for checking the correct working of the stability instrument. Steps to be performed: If an Administration's representative is not present for the stability instrument check. The results should be verified as identical to the results in the approved copy of the test conditions. The relevant input and output data of the approved test condition should be replicated. The user should have the possibility to override faulty readings manually.

Masters should therefore exercise prudence and good seamanship having regard to the season of the year. If necessary. Tow line arrangements should include towing springs and a method of quick release of the tow. The negative effect on stability of filled pool tanks should be taken into consideration. Deck cargo on board the towing ship should be so positioned as not to endanger the safe working of the crew on deck or impede the proper functioning of the towing equipment and be properly secured.

It is advisable to avoid excessive values of metacentric height. All portable deadlights should be maintained in good condition and securely closed in bad weather. Chapter 5. In such cases. Slack tanks may. Operational provisions against capsizing and to safe carriage of the cargo.

Hatch covers and flush deck scuttles in fishing vesselsshould be kept properly secured when not in use during fishing operations. If freeing ports are not sufficient for the drainage of the well. These waves are particularly dangerous. If anti-heeling measures e. Guidance on the use of anti-heeling measures should be provided in the stability booklet. The method should be simple to use. Freeing ports provided with closing appliances should always be capable of functioning and are not to be locked.

Chapter 6. Vessels intended for operation in areas where ice is known to occur should be: A chart to illustrate the areas is attached at the end of this chapter.

For vessels operating in areas where ice accretion may be expected: Chapter 6 - Icing considerations. Brief survey of the causes of ice formation and its influence upon the seaworthiness of the vessel. The most common cause of ice formation is the deposit of water droplets on the vessel's structure. These droplets come from spray driven from wave crests and from ship-generated spray. It should be borne in mind that the most dangerous geographical areas as far as ice formation is concerned are the sub-Arctic regions.

In beam and quartering winds, ice accumulates more quickly on the windward side of the vessel, thus leading to a constant list which is extremely dangerous. Examples of the weight of ice formation on a typical fishing vessel of displacement in the range tonnes to tonnes are also given. For larger vessels the weight will be correspondingly greater. Under these conditions the intensity of ice accumulation can lie within the range 1. Icing considerations 6. In any case. Under these loads the deflections should not be more than 0.

For vessels of intermediate length the minimum height should be obtained by linear interpolation. Such hatchways should be kept as small as practicable and the covers should be permanently attached by hinges or equivalent means and be capable of being rapidly closed or battened down. The height above deck of hatchway coamings on exposed parts of the superstructure deck should be at least mm. For vessels of intermediate length the minimum acceptable reduced height for sills in doorways on the working deck should be obtained by linear interpolation.

Where operating experience has shown justification and on approval of the competent authority. The height above deck of sills in those doorways. Considerations for watertight and weathertight integrity 7. A notice should be attached to the door on each side stating that the door should be kept closed at sea. All access openings in bulkheads of enclosed deck erections. The means of securing windows and the width of the bearing surfaces should be adequate. Openings leading to spaces below deck from a wheelhouse whose windows are not provided with the protection required by 7.

Skylights leading to machinery spaces should be avoided as far as practicable. The open inboard end of any discharge system should be above the deepest operating waterline at an angle of heel satisfactory to the competent authority.

The means for operating the valve with a positive means of closing should be provided with an indicator showing whether the valve is open or closed. Such a valve is not required if the competent authority considers that the entry of water into the vessel through the opening is not likely to lead to dangerous flooding and that the thickness of the pipe is sufficient.

Having regard to the size and disposition of the openings and the design of the closing devices. Openings other than hatchways. All pipes between the shell and valves should be of steel. Normally each separate discharge should have an automatic non-return valve with a positive means of closing it from a readily accessible position. Controls should be readily accessible and should be provided with indicators showing whether the valves are open or closed. Suitable warning devices should be incorporated to indicate leakage of water into the space.

Considerations for watertight and weathertight integrity machinery space openings. The height above deck of machinery space ventilator openings should be to the satisfaction of the competent authority. On the working deck the height above deck of coamings of ventilators. Companionways should be situated as close as practicable to the centreline of the vessel.

When the height of such ventilators may interfere with the working of the vessel their coaming heights may be reduced to the satisfaction of the competent authority.

Ventilators should be arranged as close to the vessel's centreline as possible and. Openings of such pipes should be protected by efficient means of closing. Air pipes on the exposed cargo and forecastle decks should be fitted with automatic closing devices. Lower edges of freeing ports should be as near the deck as practicable. Preferably they should be fitted in a position above the superstructure deck. The competent authority may accept reduction of the height of an air pipe to avoid interference with the fishing operations.

Size of opening and means provided for removal of these protective arrangements should be to the satisfaction of the competent authority. If devices are considered necessary for locking freeing port covers during fishing operations they should be to the satisfaction of the competent authority and easily operable from a readily accessible position. B In addition.

Pound boards should be so constructed that they can be locked in position when in use and will not hamper the discharge of shipped water.