QUESTIONS	487
65. Describe   the   stern   tube   of  a   steamship   and how water is
prevented from entering the ship.
66   How is the tail end shaft lubricated7
 67.	How is a propeller unshipped in dry dock?
 68.	How is the thrust of the propeller communicated to the ship's
hull?
 69.	Describe the bilge and tank drainage system of a vessel you
have served in.
 70.	Who controls the inlet and outlet valves of tanks and bilges,
and where is the valve chest usually placed?
71   What are strum boxes and what precautions must be taken with
them?
 72.	Why are long pipes in a vessel not usually straight throughout
their length?
 73.	How   is   the   depth  of  water  in  the   various  compartments
ascertained and who attends to this?
 74.	What should be done before ballast tanks are run up?
 75.	What special   arrangement  is fitted to the air pipes of cargo
oil tanks?
 76.	Describe a system of ventilation adopted in some large passenger
ships.
 77.	How is the stokehold and engine room ventilated?
 78.	Describe the special features of a vessel constructed on the
Isherwood principle.
 79.	What is corrosion and what parts of the ship are most subject
to its effect ?
 80.	How is steel work prepared before coating it with paint ?
 81.	Name some of the paints used at sea and state why different
kinds of paint are used for different purposes.
 82.	What priming coat would you give to (a)  bare  iron or steel;
(b) new woodwork on deck; (c) the funnel.
 83.	Give   a   description   of   any   underwater   compositions,   the
preparation of the shell plating and method of applying the bottom
coatings when the ship is in dry dock.
 84.	What is the difference between anti-corrosive, anti-fouling and
boot topping compositions, and state why each is used ?
85.	A butt strap on the shell plating shows signs of leaking, what
would you do 1