Propellers and RuddersRecap

Question 1

State the range of engine revolutions at which the following diesel engines run:
1) Slow speed engine
2) Medium speed engine
3) a highspeed diesel engine

Answer 1

1) 150 rpm
2) 350-650 rpm
3) 900-1200 rpm

Question 2

What are the advantages of a slow speed diesel engine?

Answer 2

Good at developing ahead power
Connected directly to prop shaft – no need for gear box, easier maintenance and cheaper to build
Cheaper to run as they burn heavy fuel oil

Question 3

What are the disadvantages of a slow speed diesel engine?

Answer 3

Poor to respond to speed reductions
Cannot run at very low revs
Whole engine must be run backwards to gain astern power ie must be stopped and is
limited by size of air bottle
Runs at pre set revs

Question 4

Describe a fix pitch propeller.

Answer 4

Cast in one piece
Fixed pitch
Pitch/angle of blade varies from root to tip
Designed to run at a particular speed

Question 5

Describe a controllable pitch propeller (CPP) or variable pitch propeller.

Answer 5

Cast as a number of separate pieces
Each blade bolted onto the central boss
Pitch varies from root to tip
Designed to give optimum performance over a range of revs

Question 6

State at what point in general (ie at how many degrees) a single rudder would stall

Answer 6

35˚ ~ 45º.

Question 7

Name and sketch an example of a variable profile rudder

Answer 7

Schilling (Fish profile)

Question 8

State how a variable profile rudder differs from a single rudder.

Answer 8

Effective over a much larger angle ie stalls @ around 70º.

Question 9

Name one other type of rudder that increases the effective angle that it will operate through and state
how this is achieved

Answer 9

Active rudder – achieved by the addition of an independently moveable flap.