Section 9 Deck drainage

9.1.1 Where bulwarks on the weather portions of freeboard or superstructure decks form wells, ample provision is to be made for rapidly freeing the decks of large quantities of water by means of freeing ports, and also for draining them.

9.2.1 The minimum freeing area on each side of the craft for each well on the freeboard deck or raised quarter deck, where the sheer in the well is not less than the standard sheer required by the International Convention on Load Lines, 1966, is to be derived from the following formulae:

1. where the length, , of the bulwark in the well is 20 m or less:

   area required = 0,7 + 0,035 m²

2. where the length, , exceeds 20 m

   area required = 0,07 m²

   need not be taken greater than 0,7L _L, where L _L is the length of the craft as defined in Pt 3, Ch 1, 6.2 Principal particulars.

9.2.2 If the average height of the bulwark exceeds 1,2 m or is less than 0,9 m, the freeing area is to be increased or decreased, respectively, by 0,004 m² per metre of length of well for each 0,1 m increase or decrease in height respectively.

9.2.3 The minimum freeing area for each well on a first tier superstructure is to be half the area calculated from Pt 3, Ch 4, 9.2 Freeing port area 9.2.1.

9.2.4 Two-thirds of the freeing port area required is to be provided in the half of the well nearest to the lowest point of the sheer curve.

9.2.5 When the deck has no sheer, the minimum freeing area for each well calculated from Pt 3, Ch 4, 9.2 Freeing port area 9.2.1 is to be increased by 50 per cent. Where the sheer is less than the standard the percentage shall be obtained by linear interpolation. The freeing area is to be spread along the length of the well.

9.2.6 Where the length of the well is less than 10 m, or where a deckhouse occupies most of the length, the freeing port area will be specially considered but in general need not exceed ten per cent of the bulwark area.

9.2.7 Where it is not practical to provide sufficient freeing port area in the bulwark, particularly in small craft, credit can be given for bollard and fairlead openings where these extend to the deck.

9.2.8 Where a craft fitted with bulwarks has a continuous trunk, or hatch side coamings that are continuous, or substantially continuous, the minimum freeing area is to be not less than 20 per cent of the total bulwark area where the width of trunk or hatchway is 0,4B or less, and not less than 10 per cent of the total bulwark area when the width of the trunk or hatch is 0,75B or greater. The freeing area required for an intermediate width of trunk or hatch is to be obtained by linear interpolation.

9.2.9 Where the trunk referred to in Pt 3, Ch 4, 9.2 Freeing port area 9.2.8 or its equivalent is included in the calculation of freeboard, open rails are to be fitted for at least 50 per cent of the length of the exposed part of the weather deck. Alternatively, if a continuous bulwark is fitted, the minimum freeing area is to be at least 33 per cent of the bulwark area. The freeing area is to be placed in the lower part of the bulwark.

9.2.10 Where a deckhouse has a breadth less than 80 per cent of the beam of the craft, or the width of the side passageways exceed 1,5 m, the arrangement is considered as one well. Where a deckhouse has a breadth equal to or greater than 80 per cent of the beam of the craft, or the width of the side passageways does not exceed 1,5 m, or when a screen bulkhead is fitted across the full breadth of the craft, this arrangement is considered as two wells, before and abaft the deckhouse.

9.2.11 Adequate provision is to be made for freeing water from superstructures which are open at either or both ends and from all other decks within open or partially open spaces in which water may be shipped and contained.

9.2.12 Suitable provision is also to be made for the rapid freeing of water from recesses formed by superstructures, deckhouses and deck cargo arrangements, etc. in which water may be shipped and trapped. Deck gear, particularly on fishing craft, is not to be stowed in such a manner as to obstruct unduly the flow of water to freeing ports.

9.2.13 The lower edges of freeing ports are to be as near to the deck as practicable, and should not be more than 100 mm above the deck.

9.3.1 The effectiveness of the freeing port area in bulwarks of craft not fitted with a continuous deck obstruction, depends on the free flow across the deck.

9.3.2 The free flow area is the net total longitudinal area of the transverse passageways or gaps between hatchways and superstructures or deckhouses, due account being made for any obstructions such as equipment or other fittings. The height of passageways or gaps used in the calculation of the area is the height of the bulwark.

9.3.3 The provision of freeing area in bulwarks is to be related to the net free flow area as follows:

1. If the free flow area is equal to, or greater than the freeing port area calculated from Pt 3, Ch 4, 9.2 Freeing port area 9.2.8 when the hatchway coamings are continuous, then the minimum freeing area calculated from Pt 3, Ch 4, 9.2 Freeing port area 9.2.1 is sufficient.

2. If the free flow area is less than the freeing port area calculated from Pt 3, Ch 4, 9.2 Freeing port area 9.2.1, then the minimum freeing area is to be that calculated from Pt 3, Ch 4, 9.2 Freeing port area 9.2.8.

3. If the free flow area is less than the freeing port area derived from (a) but greater than that derived from (b), the minimum freeing area, F, in the bulwark is to be obtained from the following formula:

   
   where

   F 1	=	minimum area from Pt 3, Ch 4, 9.2 Freeing port area 9.2.1
   F 2	=	minimum area from Pt 3, Ch 4, 9.2 Freeing port area 9.2.8
   f p	=	total net area of passages and gaps between hatchways, superstructures and deckhouses (the free flow area)

9.4.1 Scuppers, sufficient in number and size to provide effective drainage, are to be fitted in all decks.

9.4.2 Scuppers draining weather decks and spaces within superstructures or deckhouses not fitted with efficient weathertight doors are to be led overboard.

9.4.3 Scuppers and discharges which drain spaces below the freeboard deck, or spaces within intact superstructures or deckhouses on the freeboard deck fitted with efficient weathertight doors, may be led to the bilges in the case of scuppers, or to suitable sanitary tanks in the case of sanitary discharges. Alternatively, they may be led overboard provided that:

1. the freeboard is such that the deck edge is not immersed when the craft heels to 5^o, and

2. the scuppers are fitted with a positive control valve or automatic non-return valve at the shell preventing water from passing inboard.

9.4.4 In craft where an approved fixed pressure water spray fire-extinguishing system is fitted in vehicle or cargo spaces, deck scuppers of not less than 150 mm diameter are to be provided port and starboard, spaced about 9,0 m apart. The scupper area will require to be increased if the design capacity of the drencher system exceeds the Rule required capacity by 10 per cent or more. After installation, the two adjacent sections with the greatest aggregate drencher capacity are to be tested in operation to ensure that there is no build-up of water on the deck. The scuppers are to be led inboard to tanks or, alternatively they may be led overboard providing they comply with Pt 3, Ch 4, 9.4 Scupper arrangements 9.4.3 and Pt 3, Ch 4, 9.4 Scupper arrangements 9.4.3.(b). Inboard draining scuppers do not require valves but are to be led to suitable drain tanks (water contaminated with petrol or other flammable substance is not to be drained to machinery spaces or any other space where a source of ignition may be present) and the capacity of the tanks is to be sufficient to hold approximately 20 minutes of drenching water. The arrangements for emptying these tanks are to be approved and suitable high level alarms provided. The mouth of the scupper is to be protected by bars.

9.4.5 Scupper pipes from the weather decks discharging overboard below or near the waterline are to be provided with an automatic non-return valve at the shell. This valve may be omitted where the piping has a minimum wall thickness of:

• 7,0 mm for pipes of 80 mm external diameter or smaller;
• 10,0 mm for pipes of 180 mm external diameter;

Intermediate minimum thicknesses are to be determined by linear interpolation.

9.4.6 For the use of non-metallic pipe, see Pt 15, Ch 1, 8 Plastic pipes and Pt 15, Ch 1, 15 Requirements for small craft which are not required to comply with the HSC Code, as applicable.

9.5.1 Where the height of freeing ports is greater than 230 mm, vertical bars spaced approximately 230 mm apart may be accepted, as an alternative to a horizontal rail, to limit the height of the freeing port. Other equivalent arrangements will be specially considered.