Section 1 - Introduction

Question 1

The ultimate test is that the ship shall perform at the required speed …

Answer 1

… with mininum shaft power.

Question 2

The assumption that a hull form is optimum in calm water will also be optimum in rough seas …

Answer 2

… is not necessarily valid.

Question 3

In general, the basic contractual obligation laid on the shipbuilder is that the ship may achieve a ___________ with ___________ in good weather on trial, and for this reason ___________ performance is of great importance.

Answer 3

certain speed / specified power / smooth water

Question 4

The effect of sea condition is customarily allowed for by the provision of a ________________ above the power required in smooth water.

Answer 4

service power margin

Question 5

Resistance of a ship at a given speed is ..

Answer 5

.. force required to tow the ship at that speed in smooth water, assuming no interference from the towing ship.

Question 6

Bare-hull resistance

Answer 6

when hull has no appendages

Question 7

Tow-rope or effective power

Answer 7

power necessary to overcome the resistance

Question 8

Components of the total calm water resistance:

Answer 8

• frictional
• wave-making
• eddy
• air resistance

Question 9

Residuary resistance

Answer 9

eddy and wave-making taken together

Question 10

Simplest case of resistance

Answer 10

streamlined body moving in a straight horizontal line at constant speed, deeply immersed

Question 11

Concerning submerged bodies, since there is no __________ , there is no _____________and therefore no _____________ resistance.

Answer 11

free surface / wave formation / wave-making

Question 12

Perfect fluid

Answer 12

• without viscosity
• no eddy resistane
• no frictional resistance

Question 13

In a perfect fluid, the pressure distribution around a submerged body can be determined theoretically from considerations of the _______________.

Answer 13

potential flow

Question 14

Since the fluid has been assumed to be without viscosity , the pressure forces will be everywhere be _____________ to the hull.

Answer 14

normal

Question 15

In a real fluid the boundary layer alters the virtual shape and length of the __________, the pressure distribution there is changed and its forward component is ___________.

Answer 15

stern / reduced

Question 16

There is therefore a net force on the body acting against the motion, giving rise to a resistance which is variously referred to as ___________ or ______________.

Answer 16

form drag / viscous pressure drag

Question 17

Types of resistance the body experiences in a real fluid:

Answer 17

• frictional resistance
• eddy resistance
• form drag or viscous pressure drag

Question 18

Boundary layer

Answer 18

layer of water, which get gradually thicker from the bow to the stern, and in which the velocity varies from that of the body at its surface to that appropriate to the potential flow pattern at the outer edge of the layer

Question 19

If the body is blunt at the aft end, the flow may leave the form at some point, called ___________________, thus reducing the pressure on the after body and adding to the resistance.

Answer 19

separation point

Question 20

A ship moving in the surface of the sea experiences ____________, ____________, _____________ and _____________ in the same way as does submerged body.

Answer 20

frictional resistance / eddy-making / separation / viscous pressure drag

Question 21

A surface ship has a _____________ pressure acting over the bow, and the pressure increase at the stern, in and just below the surface, is always ___________ than a submerged body.

Answer 21

greater / less

Question 22

The presence of the ________________ modifies the skin friction and other resistances.

Answer 22

wave systems