Page 252 - Ship Construction.DJ Eyres 6Ed

Ch21-H8070.fm Page 241 Wednesday, October 18, 2006 6:59 AM
Aft End Structure 241
RUDDER STOCK Rudder stock may be of cast or forged steel, and its
meter is determined in accordance with the torque and any bending
moment it is to withstand. At its lower end it is connected to the rudder by a
horizontal or vertical bolted coupling, the bolts having a cross-sectional area
which is adequate to withstand the torque applied to the stock. This cou-
pling enables the rudder to be lifted from the pintles for inspection and service.

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RUDDER BEARING The weight of the rudder may be carried partly
by the lower pintle and partly by a rudder bearer within the hull. In some
งานห้องสมุด ศูนย์ฝกพาณิชย์นาวี
rudder types, for example, the spade type which is only supported within
the hull, the full weight is borne by the bearer. A rudder bearer may incor-
porate the watertight gland fitted at the upper end of the rudder trunk as
shown in Figure 21.5. Most of the rudder’s weight may come onto the
bearer if excessive wear down of the lower pintle occurs, and the bearers
illustrated have cast iron cones which limit their wear down.

RUDDER TRUNK Rudder stocks are carried in the rudder trunk, which
as a rule is not made watertight at its lower end, but a watertight gland is
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fitted at the top of the trunk where the stock enters the intact hull (Figure
21.5). This trunk is kept reasonably short so that the stock has a minimum
unsupported length, and may be constructed of plates welded in a box form
with the transom floor forming its forward end. A small opening with water-
tight cover may be provided in one side of the trunk which allows inspection
of the stock from inside the hull in an emergency.

Steering Gear

Unless the main steering gear comprises two or more identical power units,
every ship is to be provided with a main steering gear and an auxiliary steer-
ing gear. The main steering gear is to be capable of putting the rudder over
from 35° on one side to 35° on the other side with the ship at its deepest
draft and running ahead at maximum service speed, and under the same
conditions from 35° on either side to 30° on the other side in not more than
28 seconds. It is to be power operated where necessary to meet the above
conditions and where the stock diameter exceeds 120 mm. The auxiliary
steering gear is to be capable of putting the rudder over 15° on one side to
15° on the other side in not more than 60 seconds with the ship at its deep-
est draft and running ahead at half the maximum service speed or 7 knots
whichever is greater. Power operated auxiliary steering gear is required
if necessary to meet the forgoing requirement or where the rudder stock
diameter exceeds 230 mm.