Section 6 Watertight Integrity

Transcription

1 Contents Section 6 Watertight Integrity 3 Introduction 3 Openings in watertight bulkheads 3 Hull and deck openings 4 Maintenance of watertight integrity 8 Nautical Knowledge Watertight Integrity 1 DEC, 2002

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3 Section 6 Watertight Integrity Introduction A vessel floats because of the water it displaces. That is it only floats because it creates a hole in the ocean. If that hole fills with water the vessel sinks. Watertight Integrity is all about keeping the water out. This section details some of the methods of how we keep the water out, or maintain our Watertight Integrity. Openings in watertight bulkheads Openings may be necessary in watertight bulkheads to allow the passage of pipes or electrical cables, and special arrangements are made to ensure that the watertight integrity of the bulkhead is maintained. All pipes passing through a watertight bulkhead must be flanged to the bulkhead and do not pass directly through it (see Figure 1). The pipe on the left has a valve incorporated in it for filling the tank on the other side of the bulkhead. There is a spindle running up to the main deck from where this valve can be operated. The siting of the valve outside of the tank it is servicing reduces corrosion and maintenance. Figure 1: Pipes passing through watertight bulkhead Nautical Knowledge Watertight Integrity 3 DEC, 2002

4 Doors may also be necessary, in watertight bulkheads, to allow the vessel to continue its normal operation whilst at sea. These doors can be of either a sliding or hinged type and must be capable of operation from both sides of the bulkhead (see Figure 2). Figure 2: Internal watertight door Hull and deck openings Access hatchways Figure 3 shows the hatchways on the fore deck of a vessel that provide access to compartments below the main deck. 4 Nautical Knowledge Watertight Integrity DEC, 2002

5 Figure 3: Access hatchways on fore deck Hatchways must have a raised coaming to reduce the amount of water that could enter the ship should a wave wash over the deck while the hatch was opened. The height of the coaming varies according to the ship s length. Figure 4: Raised coaming Nautical Knowledge Watertight Integrity 5 DEC, 2002

6 Figure 4 shows a cut away section of a hatchway coaming. When a hatchway is cut into the deck of a vessel, the corners are rounded to reduce stresses. Weathertight Doors Doors providing access from the main deck to lower compartments must have sills, which serve the same purpose as hatchway coamings. The sill heights are the same as for hatch coamings. Access doors can be hinged and should be marked THIS DOOR IS TO BE KEPT CLOSED AT SEA (see Figure 5). Figure 5: External Weathertight Door 6 Nautical Knowledge Watertight Integrity DEC, 2002

7 Ventilators and air pipes Ventilators must be a minimum height above the deck and must have some means of making them watertight. This may be metal flaps, or in smaller vessels, wooden plugs and canvas covers. Air pipes, where exposed, should be of substantial construction and if the diameter of the bore exceeds 30 mm bore then the pipe should be provided with means of closing watertight. Side scuttles (portholes) All portholes below the main deck should have hinged metal covers (deadlights) that can be closed watertight. Access openings in the hull In Figure 6 the loading hatch in the side of the hull is bolted and secured while at sea. An alarm system is fitted which will sound on the bridge if the door is opened. Figure 6: Opening in the hull Nautical Knowledge Watertight Integrity 7 DEC, 2002

8 Figure 7: Watertight door open alarm switch Figure 7 shows a closer view of the trip switch that will sound the alarm if the side door were opened while at sea. Scuppers, inlets and discharges All sea inlets are to be fitted with valves of steel or material of equivalent strength attached direct to the hull or approved skin fittings (in case of non metal hulls). Drainage arrangements from weather decks Weather decks are to be provided with freeing ports, open rails or scuppers capable of rapidly clearing the deck of all water under all weather conditions. Maintenance of watertight integrity Watertight integrity can be breached through any activity or happening that allows the ingress of water in unwanted areas or compartments of the vessel. Typical examples include: Lack of maintenance to seals, screw threads and other locking devices. Damage caused by collision, grounding or heavy weather. 8 Nautical Knowledge Watertight Integrity DEC, 2002

9 Leaving hatches, doors, vents etc open. Blocked freeing ports or scuppers. Cracks along welds in metal vessels or loss of caulking from planked seams in timber vessels. Maintenance and survey requirements It is obvious that for a vessel to float, water must be prevented from gaining entry into the hull. The vessel designer has to ensure that under normal use water will not enter the hull in sufficient quantities to sink it. The shipbuilder ensures that is of sound construction to meet these requirements. This is verified at the initial survey carried out by an Authority. It is your responsibility to ensure that your vessel s watertight and weathertight integrity is maintained throughout its period of service. This is ensured by periodic surveys carried out by the survey authorities. In general terms, the survey requirements require the vessel to be watertight below the freeboard deck and weathertight above the freeboard deck. This means that the shell plating must be intact and the closures to all openings leading to the hull should be in efficient working order. No alterations should be done to any structure that would adversely affect the watertight integrity of the hull without the approval of the appropriate survey authority. It is essential that you are thoroughly familiar with the locations and closing mechanisms of all openings on your vessel through which water may enter the hull. This way you will not neglect to maintain, test and check the efficiency of any of the closing arrangements. Maintenance items Check that all access openings at ends of enclosed structures are in good condition. All door clips, clamps, and hinges should be free and well greased. All gaskets and watertight seals should be crack free. Ensure that the doors open from both sides. Figure 8 shows the typical components of a weathertight door. Nautical Knowledge Watertight Integrity 9 DEC, 2002

10 Figure 8: Weathertight door on Main deck Check all cargo hatches and access to holds for weathertightness. Seals should never be painted. Regularly inspect all machinery space openings on exposed decks. Check that any manholes and flush scuttles are capable of being made water-tight. Check that all ventilator openings are provided with efficient weathertight closing appliances and repair any defects. All airpipes of diameter exceeding 30mm bore, must be provided with permanently attached satisfactory means for closing the openings. Ensure that the non-return valves on overboard discharges are operating in a satisfactory manner. Check that all freeing ports are in a satisfactory condition, eg shutters are not jammed, hinges are free and that pins are of noncorroding material. Check that any securing appliances, if fitted, work correctly. 10 Nautical Knowledge Watertight Integrity DEC, 2002

11 Check your progress 1 What is the purpose of sills and coamings? 2 What do you understand by Watertight Integrity? Check your answers with those given at the end of this learning resource. Nautical Knowledge Watertight Integrity 11 DEC, 2002