Pitch Propellors, Water Jet Thrusters
With reference to controllable pitch propellers:
(a) describe a mechanism that changes the pitch of the blades;(7)
(b) explain how the pitch of the blades is indicated.(3)
1.Quiz. Study Notes
With reference to controllable pitch propellers:
(a) explain why they should maintain a small amount of pitch when in the neutral position;(3)
(b) state, with reasons, the failsafe position;(4)
(c) explain how pitch may be restored should hydraulic system failure occur.(3)
2.Quiz. Study Notes
With reference to a vessel with a single electro/hydraulic controllable pitch propeller, explain EACH of the following:
(a) how manoeuvring may be maintained if the control system fails;(5)
(b) the action to be taken should the hydraulic system irreparably fail whilst on route and the blades assume zero pitch.(5)
Question 6.
Some do not understand the term Electro-Hydraulic. Some use engines to manoeuvre even though the question states a single CPP. There is more to maintaining manoeuvring than just switching to the local control. The question states that the CPP assumes zero pitch on failure of the hydraulics – this is therefore the fail safe position. Several appear to have a further spring in the hub to give pitch on the blade.
3.Quiz. Study Notes
With reference to controllable pitch propellers:
(a) describe a mechanism that changes the pitch of the blades; (7)
(b) explain how the pitch of the blades is indicated.(3)
Question 6. Several answer this question by describing the whole system, the question just asks about the mechanism for changing the blade angle. Of those that describe the mechanism, most mention longitudinal movement and angular but none actually explain how longitudinal is changed to angular. Several make no attempt
4.Quiz. Study Notes
With reference to propellers, explain EACH of the following:
(a) TWO advantages of having high skew;(5)
(b) TWO advantages of aft rake.(5)
5.Quiz. Study Notes
(a) State SIX advantages of controllable pitch propellers.(6)
(b) State FOUR disadvantages of controllable pitch propellers.(4)
6.Quiz. Study Notes
With reference to propellers, explain EACH of the following terms:
(a) skew;(2)
(b) rake;(2)
(c) pitch;(2)
(d) slip.(4)
7.Quiz. Study Notes
(a) Sketch an arrangement for a transverse, water jet thruster.(6)
(b) Explain how thrust is created in a water jet thruster.(4)
8.Quiz. Study Notes
Describe the advantages of using water jets instead of conventional propellers for vessel propulsion.(10)
Question 6. Many simply state advantages the question says ‘describe”. Many of the advantages claimed could be equally applied to CPP’s and D/E drives, both of which are now considered conventional.
9.Quiz. Study Notes
Describe, with the aid of a sketch, the operation of a transverse thruster that is hydraulically driven.(10)
Question 6. Generally poor answers. Several just describe the hydraulic control, describing operation must include how thrust is varied in magnitude and direction as well as control.
10.Quiz. Study Notes
(a) Describe, with the aid of a sketch, a pilgrim nut.(5)
(b) Explain how the pilgrim nut is used to ensure correct fitting of a keyless propeller.(5)
11.Quiz. Study Notes