El número tres

Up to 250 mm 1.2 mm

251 mm to 600 mm 1.6 mm

Over 600 mm 2.0 mm

(2) Where the longest sides are 500 mm to 750 mm in length the trunking is to be stiffened by a 1.6 mm thick, swaged plate, riveted longitudinally along the centre of the sides, or by the use of swaged trunking.

(3) Trunking with the longest side in excess of 750 mm is to be divided longitudinally by a plate, of similar thickness and material to that of the trunk, riveted or welded, as appropriate, throughout its length. Where the aspect ratio of the trunk is greater than two, lightening holes may be cut in the longitudinal dividing plate to reduce weight.

(4) Transverse joints are to be riveted slip, bolted flange, or where the thickness of the material allows, a continuous butt weld. In any run of trunking, sufficient portable sections, i.e. those secured at both ends by bolted flanges, are to be incorporated to enable the total length of trunking to be cleaned when they are removed.

(5) All joints, except for those welded, are to be made airtight by the use of a suitable flexible mastic sealer.

11.3 Textile Ventilation Trunking

a. Textile ducting (also referred to as `socks') may be permeable, i.e. air is permeated through the weave of the cloth. The level of delivery is dependant on the static pressure within the sock combined with the tightness of weave.

b. Alternative textile ducting may be fitted with either slots or nozzles to distribute the air. It is possible to combine all configurations within a system to provide the required distribution.

c. The low material resistance combined with linear percolation minimises the loss of pressure.

11.3.1 Advantages

a. Efficient Air Distribution  Air is defused through the whole length of the socks providing an efficient mix of air within the compartment.

b. Draught Free  The low impulse system is based on the principle of natural air movement, dependant on temperature differentials, the cold air displaces the warmer air. Textile has the ability to handle large volumes of air which provide for a high number of change when desired.

c. Recirculation Ducting  Is not required within the compartment since superior distribution of the supply air over the whole of the compartment eliminates the need for a network of recirculation ducting. A central return air point is all that is required.

d. Energy Saving  The efficient air diffusion with the minimum of heat stratification allows for a reduced system operating period, however, the fan can be expected to continue running even when compartment temperatures are satisfied to avoid heat stratification and ensure adequate ventilation.

e. Aesthetic Appearance  Is achieved through uniform sizing of the socks, combined with a choice of colours and tailored circular, semicircular or quadrant in section, the fitting of such systems can enhance compartment decor.

f. Low Weight  Assists in ease of fitting and handling for cleaning. It can be fitted to light supporting structure, and may contribute to improved ship stability.

Conventional thermal insulation is not required, the high induction rate combined with the linear delivery means a short contact time prevents the dew point being reached. Condensation forming on the external surface even with a cold air supply is therefore avoided.

g. Reduced Air Noise  No resonance is experienced, the ducting material absorbs noise.

h. Flexible Mounting  Allows systems to be readily reconfigured if so desired. It can be easily removed in way of shipping routes or during maintenance periods to provide improved access.

i. Cleaning  Is achieved by removing the socks which are connected together into convenient lengths by the means of zips and replacing with a replacement set.

The dirty socks can be washed using a standard washing machine. Continuous air movement with no obstructions over a permeable sock will prevent dust from settling. Cleaning on a regular basis will be necessary since the weave provides a second line filtration system for the supply air. It therefore follows that quality of air provided by textile ventilation is significantly cleaner than for conventional systems.

j. Repair and Modifications  For textile trunking can be easily achieved, the cloth can be patched/stitched. Where modifications are required, additional legs can be added to meet with compartment changes.

k. Economic Storage & Transportation  Can be achieved since when packed, the socks take up relatively small volume of space. 100 metres of 800 mm cloth equates to a cubic metre.

conventional aluminium systems.

11.3.2 Disadvantages

a. Few disadvantages are thought to exist, however, patternisation of component parts has not been addressed.

b. The evolution of maintenance and cleaning of the trunking requires better management control than presently exists for conventional systems.

11.4 Gastight and Structural Trunks and Trunks Subjected to Rough Usage or High Fire Risk Including Smoke Removal Systems

a. Trunks that, in the `closed down' condition could convey contaminated air through the citadel, or serve compartments within the citadel but are routed outside of its boundaries, or pass through compartments that are

`contaminated if used', are required to be gastight.

b. Structural trunks are those built as an integral part of the ship's structure with decks and/or bulkheads being utilized as trunk sides. The thickness of the plating used to construct the other sides is to be as specified below unless strength or watertight integrity considerations dictate otherwise.

c. Trunks subjected to rough usage are typically those sited vertically in passageways and horizontally in way of hatches through which stores, machinery and other heavy/bulky items need to be transported. This category also includes those sections of trunking that have to be removed to clear shipping/unshipping routes.

d. Trunks subjected to high fire risks are typically all trunks passing through and contained within galleys, magazines, flammable stores, machinery spaces, etc.

e. These trunks are normally where thickness allows without distortion, to be manufactured of Mild SteelGalvanized After Manufacture (MSGAM), with the following exceptions:

(1) Where trunk thickness could possibly lead to distortion from galvanising after manufacture, the material may be mild steel galvanised plate with zinc spraying of destroyed galvanising at welded joints;

(2) Where trial results show that specialist, preformed, commercial kits, that use other materials such as composites, can out perform galvanized mild steel in all the relevant areas without incurring significant expense.

In these cases MOD approval is to be obtained before such commercial kits are utilized;

(3) Gastight trunking contained within the citadel may be manufactured, by the shipbuilder or his representative, using aluminium alloy of the same thickness as the alternative mild steel;

(4) Structural trunks are to be of ungalvanized, mild steel plate, continuously butt welded to the ship's structure with the interior surfaces painted in accordance with NES 763;

(5) For difficult shaped sections of trunking abrasive blasting and zinc spraying of both external and internal surfaces is an acceptable alternative to GAM.

f. Where trunks are tailormade for the ship and are manufactured by the shipbuilder or his representative the following guidelines are to be adhered to:

(1) Trunks are generally to be rectangular in shape and the thickness of the galvanized mild steel is to vary with the length of the longest side as follows:

Longest side of a rectangular trunk Material Thickness

Up to 250 mm 1.6 mm

251 to 600 mm 2.0 mm

Over 600 mm 3.0 mm

(2) Where the longest sides are 500 mm to 750 mm in length the trunking is to be stiffened by 25 x 25 x 3 mm angle, intermittent welded, longitudinally, along the centre of the sides;

(3) Trunking with the longest side in excess of 750 mm is to be subdivided longitudinally by a welded plate of the same material and thickness as that of the trunk. Where the aspect ratio of the trunk is greater, then two lightening holes may be cut in the longitudinal dividing plate to reduce weight;

(4) Longitudinal joints are to be continuous butt weld;

(5) Transverse joints are to be a continuous butt weld or, except for structural trunks, flanged. Flanges are to be welded to the trunk and joints are to be made gastight by using a suitable flexible mastic sealer with a silicon covered fibre woven cloth.

11.5 Watertight Trunks

a. Watertight trunks are to be installed, in accordance with NES 119 Part 1, to ensure the integrity of the vessel's watertight subdivision and to contain flooding within the Red Risk Zone or `V' lines as indicated in the relevant Subdivision Policy Paper.

b. These trunks are normally to be rectangular in shape, manufactured of MSGAM, the thickness of the material varying with the longest side of trunk as follows:

Longest side of a rectangular trunk Material Thickness

Up to 250 mm 1.6 mm

251 to 400 mm 2.0 mm

Over 400 mm 3.0 mm

c. Stiffening, longitudinal subdivision, transverse and longitudinal joints are to be as specified for gastight trunks that are manufactured by the shipbuilder or his representative.

11.5.1 Trunk Installation.

a. When installed the interior surfaces of the trunks are to be smooth, free of obstructions and, with the exception of structural trunk, left unpainted.

b. All trunks are to be well supported, hangers being spaced 2.0 m to 2.5 m apart and at the ends of trunks that are connected to removable sections. Hangers are to completely encircle the trunking and where insulation is fitted they are to only be in contact with the external surface, care being taken to ensure that they do not provide a `thermal bridge' between trunk and atmosphere (See Figure 11.1).

c. Where dissimilar metals have to be connected together, the preparation of the faying surfaces is to ensure that the risk of corrosion is minimal. The preferred method is for the surfaces to be degreased, etched and coated with a proven corrosion inhibitor.

d. In each system drain plugs are to be provided at low points in the trunking where water may collect and self draining terminals are to be fitted at weather openings.

e. Watertight butterfly valves, selected from NES 360, are to be fitted as required to maintain the integrity of watertight and gastight structure. These valves are normally to be fitted directly to the bulkhead or deck but in exceptional circumstances a distance piece or coaming, manufactured from material of the same type and thickness as that of the bulkhead or deck, may be used.

f. Where trunking must pass through a strength deck or major bulkhead the opening is to be sited, shaped and strengthened in accordance with NES 155 Part 1. To reduce the size of the opening, and consequently the size and weight of the butterfly valve, if fitted, the trunking either side of the bulkhead or valve may be in the form of a circular `Venturi' section.

g. All trunks that pass through major bulkheads and decks but are not fitted with a isolating valve at the point of penetration are to be provided with portable sections to enable the ventilation to be blanked in order to periodically air test the integrity of the compartments where required.

h. Textile trunking should only be installed in areas of high fire risk/rough usage after consultation with the DA and the sponsor of this NES.

11.6 Vulnerability

a. To give ready access to ship's side plating and to minimize possible damage, trunks, pipes and fittings, associated with ventilation and airconditioning systems, are to be sited well away from the ship's side in the Red Watertight Risk Zone especially on or near the waterline. They are also to be sited clear of the after sides of collision bulkheads from below to well above the deep waterline.

b. Textile trunking may be fitted in compartments below the waterline but due consideration must be given to the effect of damaged trunking on emergency pumps.

WELDED TO DECKHEAD M6 NUT & LOCKING NUT

INSULATION

HANGAR SUPPORT FOR TRUNKING 150 mm TO 300 mm WIDTH

VENT TRUNK

M6 ROOFING BOLT 25 mm x 3mm M.S. STRAP

95x2 mm M.S.

SADDLE (GALVANISED)

UP TO 150 mm 50x2 mm M.S.

SADDLE FOR WIDTH

25 mm x 3 mm M.S. STRAP WELDED TO DECKHEAD

M6 NUT & LOCKING NUT

M6 ROOFING BOLT

STIFFENING ARRANGEMENT TO SADDLE FOR TRUNKING OVER 300 mm WIDTH

95x2 mm M.S.

(GALVANISED) SADDLE

SNAPED END PLATES

2 mm M.S. SWAGED STIFFENER SEALED EACH END, IF REQUIRED POP RIVETS

VENTILATION TRUNKING &

NOTE :

INSULATION NOT SHOWN