Section 5 Air pipes, ventilator pipes and their securing devices located on the exposed fore deck

5.1.1 For the application of the following requirements relating to ventilators, see Pt 3, Ch 12, 2.1 General 2.1.1. For the application of the following requirements relating to air pipes, see Pt 3, Ch 12, 3.1 General 3.1.1. Air pipes complying with the following requirements are also to comply with the applicable requirements of Pt 5, Ch 13, 12 Air, overflow and sounding pipes and Pt 5, Ch 15, 2.5 Air and sounding pipes.

5.1.2 Special care is to be taken in the design and positioning of ventilator openings and coamings, particularly in the region of the forward end of superstructures and other points of high stress. The deck plating in way of the coamings is to be efficiently stiffened.

5.1.3 Ventilators from deep tanks and tunnels passing through ’tween decks are to have scantlings suitable for withstanding the pressures to which they may be subjected, and are to be made watertight.

5.1.4 For height and location of cargo tank vent outlets, see Pt 5, Ch 15, 4 Cargo tank venting, purging and gas-freeing and see also 8.2 Pressure relief systems .9 and 8.2 Pressure relief systems .10 of the Rules for Ships for Liquefied Gases, or Ch 1, 8.2 Cargo tank venting 8.2.2, of the Rules for Ships for Liquid Chemicals, where applicable.

5.1.5 On offshore supply ships, air pipes are to be situated clear of the cargo containment areas.

5.2.1 The design pressure acting on air pipes, ventilator pipes and their closing devices is to be taken as not less than:

where

ρ	=	density of sea water (1,025 t/m3)
V	=	velocity of water over the fore deck
	=	13,5 m/sec for d ≤ 0,5d 1
	=	for d > 0,5d 1
d	=	distance from summer load waterline to exposed deck
d 1	=	0,1L but need not be taken as greater than 22 m
C d	=	shape coefficient (0,5 for pipes,1,3 for air pipe or ventilator heads in general and 0,8 for an air pipe or ventilator head of cylindrical form with its axis in the vertical direction)
C s	=	slamming coefficient (3,2)
C p	=	protection coefficient (0,7 for pipes and ventilator heads located immediately behind a breakwater or forecastle and 1,0 elsewhere and immediately behind a bulwark).

5.2.2 Forces acting in the horizontal direction on the pipe and its closing device are to be not less than those calculated from Pt 3, Ch 12, 5.2 Loading 5.2.1 using the largest projected area of each component.

5.3.1 Bending moments and stresses in air and ventilator pipes are to be calculated at critical positions:

• at penetration pieces;
• at weld or flange connections; and
• at toes of supporting brackets.

5.3.2 Bending stresses in the net section are not to exceed 0,8σ_y, where σ_y is the specified minimum yield stress or 0,2 per cent proof stress of the steel at room temperature. Irrespective of corrosion protection, a corrosion addition to the net section of 2,0 mm is then to be applied.

5.3.3 For standard air pipes of 760 mm coaming height closed by heads of not more than the tabulated projected area, pipe thicknesses and bracket heights are specified in Table 12.5.1 Air pipe thickness and bracket standards. Where brackets are required, three or more radial brackets are to be fitted. Brackets are to be of gross thickness 8 mm or more, of minimum length 100 mm, and height according to Table 12.5.1 Air pipe thickness and bracket standards but need not extend over the joint flange for the head. Bracket toes at the deck are to be suitably supported.

5.3.4 For other configurations, loads according to Pt 3, Ch 12, 5.2 Loading are to be applied, and means of support determined in order to comply with the requirements of Pt 3, Ch 12, 5.3 Strength requirements 5.3.1 and Pt 3, Ch 12, 5.3 Strength requirements 5.3.2. Brackets, where fitted, are to be of suitable thickness and length according to their height. Pipe thickness is not to be taken less than as indicated in Pt 5, Ch 12 Piping Design Requirements.

5.3.5 For standard ventilators of 900 mm coaming height closed by heads of not more than the tabulated projected area, pipe thicknesses and bracket heights are specified in Table 12.5.2 900 mm Ventilator pipe thickness and bracket standards. Brackets, where required, are to be as specified in Pt 3, Ch 12, 5.3 Strength requirements 5.3.3.

5.3.6 For ventilators of coaming height greater than 900 mm, the coaming support will be specially considered. Pipe thickness is not to be taken less than as indicated in Pt 5, Ch 12 Piping Design Requirements.

5.3.7 All component parts and connections of the air pipe or ventilator are to be capable of withstanding the loads defined in Pt 3, Ch 12, 5.2 Loading.

5.4.1 The height of ventilator coamings is to be not less than 900 mm, this height being measured above deck sheathing, where fitted. In particularly exposed positions, the heights of coamings and scantlings may be required to be increased.

5.4.2 The height of ventilator coamings may be required to be increased on ships of Type ‘A’, Type ‘B-100’ and Type ‘B-60’ where this is shown to be necessary by the floatability calculations required by the Load Lines, 1966/1988 - International Convention on Load Lines, 1966, as Amended by the Protocol of 1988.

5.4.3 For gooseneck ventilators, the coaming height is to be measured to the underside of the bend, this being the lowest point through which water on deck could pass freely to spaces below.

5.4.4 Where wall vents are fitted with an internal baffle which rises above the lower edge of the exterior opening, the coaming height is measured to the top of the baffle.

5.4.5 Where permitted by the National Authority, ventilator coaming heights may be reduced on ships engaged on protected or extended protected water service. Coaming heights are to be as high as practicable, with a minimum height of 450 mm.

5.5.1 The height of air pipes from the upper surface of decks exposed to the weather, to the point where water may have access below is normally to be not less than 760 mm, this height being measured above deck sheathing, where fitted.

5.5.2 Lower heights may be approved in cases where these are essential for the working of the ship, provided that the design and arrangements are otherwise satisfactory. In such cases, efficient, permanently attached closing appliances of an approved automatic type will generally be required.

5.5.3 The height of air pipes may be required to be increased on ships of Type ‘A’, Type ‘B-100’ and Type ‘B-60’ where this is shown to be necessary by the floatability calculations required by the Load Lines, 1966/1988 - International Convention on Load Lines, 1966, as Amended by the Protocol of 1988. An increase in height may also be required or recommended by individual Administrations when air pipes to fuel oil and settling tanks are situated in positions where sea-water could be temporarily entrapped, e.g. in recesses in the sides and ends of superstructures or deckhouses, between hatch ends, behind high sections of bulwark, etc. This may entail an increase in tank scantlings, see also Pt 3, Ch 3 Structural Design.

5.5.4 Air pipes are generally to be led to an exposed deck. For alternative arrangements in an enclosed space on a main vehicle deck, see Pt 4, Ch 2, 9 Subdivision structure on vehicle deck.

5.5.5 Where air pipes are led through the side of superstructures, the opening is to be at least 2,3 m above the summer load waterline.

5.5.6 Where permitted by the National Authority, air pipe coaming heights may be reduced on ships engaged on protected or extended protected water service. Coaming heights are to be as high as practicable, with a minimum height of 450 mm.

5.6.1 All ventilator openings are to be provided with efficient weathertight closing appliances unless the height of the coaming is greater than 4,5 m.

5.6.2 In ships where the load line length, L _L (see Pt 3, Ch 1, 6.1 Principal particulars), is not more than 100 m, the closing appliances are to be permanently attached to the ventilator coaming. Where not so provided in other ships, they are to be conveniently stowed near the ventilator to which they are to be fitted.

5.6.3 Where, in ferries, ventilators are proposed to be led overboard in an enclosed ’tween deck, the closing arrangements are to be submitted for approval. If such ventilators are led overboard more than 4,5 m above the main vehicle deck, closing appliances may be omitted, provided that satisfactory baffles and drainage arrangements are provided, as in the case of air intakes or exhaust openings for machinery spaces, which may be arranged in the sides of the ship.

5.6.4 On offshore supply ships, to ensure satisfactory operation in all weather conditions, machinery space ventilation inlets and outlets are to be located in such positions that closing appliances will not be necessary.

5.6.5 Rotating type mushroom ventilator heads are unsuitable for application on the exposed fore deck.

5.6.6 Wall ventilators (jalousies) may be accepted provided they are capable of being closed weathertight by hinged steel gasketed covers secured by bolts or toggles.

5.6.7 A ventilator head not forming part of the closing arrangements is to be not less than 6,5 mm thick.

5.7.1 All openings of air pipes are to be provided with permanently attached, satisfactory means of closing to prevent the free entry of water, see also Pt 3, Ch 12, 5.5 Height of air pipes 5.5.2.

5.7.2 Closing appliances are to be of an approved automatic type where, with the ship at its summer load waterline, the openings are immersed at an angle of heel of 40° or, the angle of down flooding if this is less than 40°. see also Pt 3, Ch 3, 6 Minimum bow heights, reserve buoyancy and extent of forecastle.

5.7.3 Where the closing appliances are not of an automatic type, provision is to be made for relieving vacuum when the tanks are being pumped out.

5.7.4 In a ship to which timber freeboards are assigned, air pipes which will be inaccessible when the deck cargo is carried are to be provided with approved automatic closing appliances.

5.7.5 Pressure/vacuum valves as required by Pt 5, Ch 15, 4 Cargo tank venting, purging and gas-freeing may be accepted as closing appliances for cargo tanks.