Question

Describe with detailed Sketch the Arrangement for securing the exhaust gas uptakes in the funnel casing of a steam or motor ship

Answer.

The size and shape of the funnel depends upon the requirements of the ship owners. At one time tall funnels were fitted to steam ships to obtain the required natural draught and, in passenger ships, to ensure that the smoke and grit were carried clear of the decks. Modern ships with forced draught do not require such high funnels. The funnel has now become a feature of the design of the ship, enhancing the appearance and being a suitable support for the owners house mark. They are built much larger than necessary, particularly in motor ships where the uptakes are small. They may be circular, elliptical or pear shaped in plan view, while there are many varied shapes in side elevation. In many cases the funnel is designed to house deck stores or auxiliary machinery such as ventilating fan units.

The funnel consists of an outer casing protecting the uptakes. The outer funnel is constructed of steel plate 6 mm to 8 mm in thickness. It is stiffened internally by ordinary angles or flat bars fitted vertically. Their scantlings depend upon the size and shape of the funnel. The plating is connected to the deck by a boundary angle, while a moulding is fitted round the

top to stiffen the free edge. Steel wire stays are connected to lugs on the outside of the funnel and to similar lugs on the deck. A rigging screw is fitted to each stay to enable the stays to be tightened. A watertight door is fitted in the funnel, having clips which may be operated from both sides

(Fig. a).

Fig. a

FUNNEL CONSTRUCTION

PLAN VIEW

ARRANGEMENT OF FUNNEL UPTAKES

Fig. b

The uptakes from the boilers, generators and main engine are carried up inside the funnel and stopped almost level with the top of the funnel (Fig. b). A steel platform is fitted at a height of about 1 m inside the funnel. This platform extends right across the funnel, holes being cut in for the uptakes and access. The uptakes are not connected directly to this platform because of possible expansion, but a ring is fitted above and below the plating, with a gap which allows the pipe to slide. Additional bellows expansion joints are arranged where necessary. At the top a single platform or separate platforms may be fitted to support the uptakes, the latter being connected by means of an angle ring to the platform. In motor ships a silencer must be fitted in the funnel to the main engine exhaust. This unit is supported on a separate seat. Ladders and gratings are fitted inside the funnel to allow access for inspection and maintenance.