1888
THE NEW ZEALAND GAZETTE.
NO. 53
(2) heat passing from one side of the furnace-crown
plate to the other, (3) heat passing from the steam-
pipes in the engine-room, (4) the heat of evapora-
tion?
175. What are the effective heating-surfaces of
a marine boiler?
176. What parts of a marine engine are exposed
to danger when the temperature is below freezing-
point?
177. What precautions are necessary in cold cli-
mates when the temperature is below freezing-
point?
178. State as many ways as you can by which a
boiler might not get its full feed. A boiler, or one
of a set of boilers, gets short of water although the
feed-valve is open its proper amount : to what causes
might this be due?
179. Of what are furnace-bars generally made?
About what thickness are they at the top? About
what space is between them? Whether are the
bars put further apart for Newcastle coal or for
Welsh coal?
180. Which burns faster, Newcastle coal or Welsh
coal? Which is the flaming coal? Which makes
most smoke?
181. About how many tons of steam-coal will be
burnt per day in four furnaces, each 3 ft. wide and
of about the usual length? On what grounds do
you say so?
182. About how many tons of steam-coal will be
burnt per day with good triple-expansion engines
to drive an ordinary steamer of 40 ft. beam ten knots
an hour by steam alone? On what grounds do
you say so? What percentage more coal would
be required to propel the same steamer one knot
faster?
183. About how many tons of steam-coal will be
burnt per day with a good triple-expansion engine,
surface condensers, the low-pressure cylinder 60 in.
diameter, doing average work? On what grounds
do you say so?
184. A pair of inverted-cylinder direct-acting
engines; there is a liner half an inch thick between
the ahead eccentric-rod and the eccentric-strap;
in overhauling the engine this piece is lost and for-
gotten: what difference will its omission make in
the working of the engine, on the admission, on the
cut-off, and on the exhaust of the steam? Which
will take place earlier and which later, distinguishing
between the upstroke and the downstroke?
185. A pair of inverted-cylinder direct - acting
engines driving a right-hand screw : on which of the
cross-head guide-bars is the pressure greatest in the
upstroke, and on which in the downstroke?
186. A screw propeller is getting loose, it has a
little play on the shaft, sideways on the key or feather:
how will this show in the engine-room?
187. How would you prove whether the centre
line of the trunnions of an oscillating-cylinder be fair
with the centre line of the main shaft?
188. How can the fairness of a line of screw-
shafting be tested without lifting the shafts?
189. Where are steel forgings generally used in
marine engines?
190. What is the composition of nickel steel?
Where is it sometimes used in engines and boilers?
191. How is forced draught generated on board
ship and supplied to boiler-furnaces? Is the air
heated before delivery; if so, how?
192. What is "induced" draught? Compare
the merits of "forced" and of "induced" draughts.
193. How is the intensity of the draught mea-
sured? What is the usual pressure employed in
the mercantile marine?
194. An explosive gas is liberated from bunker
coal; usually in well-ventilated bunkers this gas
escapes into the atmosphere without doing harm, in
ill-ventilated bunkers the gas, after mixing with a
certain proportion of common air, has been known
to explode when a naked light has been brought in
contact with it: What is the composition of the gas?
Where is it found -- in bunkers, 'tween decks, pockets,
and coal-shoots? How may it be got rid of as soon
as it evolves from the coal? How many cubic feet
of air to one of the gas forms a violent explosive
mixture?
195. A lighted lamp or candle has sometimes been
lowered into an apparently empty paraffin-tank and
produced an explosion resulting in injury to the per-
son holding the light: what did the tank probably
contain, and what produced the explosion?
196. In vessels carrying coal cargoes it has been
observed that, generally speaking, the gas which
escapes from the body of the coal is found more
abundantly in the forward end of the hold than at
the after end: why should this be so?
197. In recently opened ballast-tanks, double
bottoms, and boilers a light lowered into either has
sometimes been extinguished: what would, in all
probability, cause this?
198. In double-bottom steamers where does the
bilge-water lie, and where are the roses of the bilge-
pipes fitted?
199. What is the advantage of a large rose over a
small one?
200. Why, especially in vessels carrying cargoes
liable to shift, should engine bilge-suctions be fitted
to both wings of the bilge?
201. In a heavily listed vessel, why is it difficult
to keep steam?
202. If the engine bilge-pumps get choked and
water accumulates in the stokehold bilges, what effect
does the water have upon the bilge-boards and stoke-
hold-plates when the ship is rolling violently?
203. In a triple-expansion engine what spare gear do
you consider necessary in the case of a foreign-going
ship? Also, what stores would you provide for a
voyage to England?
204. What means are sometimes provided for
temporarily coupling together the broken parts of,
say, a tunnel-shaft? Describe the fitting.
205. Does the pressure on the thrust collars vary
with the horse-power, or with the speed of the ship,
or how?
206. If the holding-down bolts of a thrust bearing
should become slack, what effect would it have upon
the working of the engines?
207. In an engine with three cranks which of the
three is subject to the greatest torsional stress (1) in
going ahead, (2) in going astern?
208. Is it usual to make the crank-shaft of a triple-
or quadruple-expansion engine in one piece? And
is the diameter of the shaft uniform from end to end?
Give your reasons for the practice which obtains.
209. In a "built" crank-shaft how are the webs
rigidly secured to the pins and to the body of shaft?
210. There are various descriptions of donkey-
engines in use on board ship for pumping purposes;
some pumps are fitted with escape-valves, some are
not: why should this be?
211. Explain the functions of an air-vessel fitted
to a feed-pump. Make rough hand sketches of (1) a
satisfactory vessel, (2) an unsatisfactory vessel,
where, say, the air-spring has been destroyed by care-
lessness, or has never been properly provided.
212. Should cocks or escape-valves be fitted to air-
vessels: why, or why not?