Page 300 - Practical Ship Design

258 Chapter 8

Ship's Nw
Hul DotkMon HYDRODYNAMICS
Drdt rim

Fig. 8.16. Seakeeping data flow diagram.

The best practical if somewhat simplistic advice would seem to be the mainten-
ance of as much deadwood aft as possible.

8.7.9 Manoeuvrability

The requirement for manoeuvrability varies with ship type and intended service.
Whilst all ships should have a reasonable minimum standard a significantly higher
performance should be specified for those intended for operation in narrow or
crowded waters. Warships whose manoeuvrability provides one of their best
defences against approaching torpedoes or missiles and the possibility of avoiding
mines seen at the last moment need a particularly good capability.
In most single-screw ships turning ability is provided by a single centreline
rudder operating in the propeller race. The performance is largely a function of the
rudder area and its relationship to the product of length x draft which provides an
approximate measure of the ship's resistance to turning. The waterline shape of the
rudder is also important and should be a streamlined aerofoil with a high lift
characteristic. Because the flow onto the rudder from the propeller is different
above and below the shaft centreline there would appear to be some advantage in
shaping the upper and lower parts of the nose of the rudder differently, and there