Page 117 - Practical Design Ships and Floating Structures

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barges ” is given in figure1 and it’s main particulars is shown in tablel. When this type ofstem is applied in shallow
waterway, the diameter of propeller can be increased so that the propulsive efficiency of ship is raised. Because
enough water flow passing through propeller can be pledged by tunnel , ship still has steady propulsive efficiency and
then it is adopted widely in rivers with shallow and rapid current. But along with the advance of technology and
appearance of new ship types, the tunneled stem presents some defects such as higher resistance, lower propulsive
factor, etc. So it is necessary to quickly develop new hull forms of cargo ship in Wujiang instead of tunneled stem.

Figure1 : Afterbody plan of tunneled stern

TABLE1
SHIP’S MAIN PARTICULARS

Afterbody Tunneled stem Tunneled combined with twin-stem
Length overall (LOA) 35.70m 39.75m
Length on waterline(LwL) 34.50m 39.00m
Breadth moulded(B) 6.60m 7.00111

Draught(T) 1.60111 1.40m
Displacement( A ) 244.04t 235.50
Block coefficient(CB) 0.61 0.62
Longitudinal prismatic coefficient (Cp) 0.677 0.623
Main Engine Type 6135ACaB 61 34AZCaB
Power(BHP) 294.2kW 294.2KW

Since 1980, a new afterbody of twin-stem has been applied widely in cargo ship, passenger ship and so
on in the middle and lower reaches of Yangtse River. By using twin-stern, propellers work in high wake
region. So ship’s quasi-propulsive coefficient(QPC) is higher. But in this afterbody ship’s D/T is still
smaller than 1, where DIT is the ratio of diameter of propeller to draught of ship. Because in waterways
with shallow and rapid current, the power of main engine is higher in general to resist rapid current. In
order to improve ship’s propulsive performance, the diameter of propeller is usually greater than
draught . While that is not contented by means of twin-stem.
As stated above, each afterbody has advantages and disadvantages. It is a key problem how to develop
an afterbody that has merits of two types of stem above. From the point of view of higher wake and great