Page 212 - Introduction to Marine Engineering

196 Deck machinery and hull equipment

carry sufficient equipment and provisions for survival for a reasonable
period (Figure 10,12). This would include oars, a boat hook, a compass,
distress rockets, first aid equipment, rations and fresh water. They must
also be partially or totally enclosed, self-righting and equipped with an
engine.
Lifeboats on cargo ships of 20 000 tons gross tonnage and above must
be capable of being launched when the ship is making headway at speeds
up to 5 knots.
A new requirement for all new ships is that a rescue boat, capable of
being launched in five minutes, must be carried. This boat is to be used
to rescue persons from the sea and also to gather together the lifeboats,
Lifeboat davits are provided as stowage for the lifeboats which can
readily be released to lower the boats without any mechanical assistance,
'Gravity davits', as they are called, slide down and position the boat for
lowering as soon as they are released. The davits must be able to lower
the boats when the ship is heeled to 15° on either side.
One type of gravity davit is shown in Figure 10.13. The lifeboat is held
against the cradle by ropes called 'gripes'. Another wire, either separate
or combined with the gripes, holds the cradle in its upper position. With
the gripes and the cradle securing device free, the winch handbrake can
be released to enable the cradle to slide down and over the ship's side. A
tricing-in pendant (a wire) bring the lifeboat close to the ship's side to
enable it to be boarded. The bowsing lines which fasten to each end of
the lifeboat are then used to hold it in to the ship's side, the tricing
pendant then being released. Once the crew are on board the bowsing
lines are released and the lifeboat lowered to the water. The wires which
raise or lower the boat are called 'falls' and the speed of descent is
restricted to 36m/min by a centrifugal brake. The handbrake used to
lower the boat has a 'dead man's handle' or weighted lever, which, if
released, will apply the brake.
Liferafts are normally provided to accommodate all of the ship's
complement. They are usually stored in cylindrical glass-reinforced
plastic containers which are secured on chocks on the deck. Inflation
takes place automatically when the container is thrown overboard, the
container bursts open and the liferaft floats clear. A pressurised cylinder
of carbon dioxide is used to inflate the raft. One type of liferaft is shown
in Figure 10.14, where it can be seen to be a well equipped totally
enclosed arrangement. The survival equipment located in the raft is
similar to that provided in lifeboats. Liferafts must normally be boarded
from the water unless they are of a special type which is lowered, fully
inflated, by a davit; but it is not usual to fit this type on cargo vessels.
Liferafts must be stowed in such a way that they will float free and inflate
if the vessel sinks. A hydrostatic release is normally used which releases
the lashings at a predetermined depth of water.