Manoevuring Flashcards
What are the advantages of a Fixed Pitch Propeller (FPP)?
Simple design
Easy to repair if a blade is damaged
Cheaper compared with other designs
Suitable for vessels whose purpose is to go straight and fast
What are the disadvantages of a Fixed Pitch Propeller (FPP)?
Require more power for higher speeds (not the most efficient)
Not suitable for vessels with high manoeuvrability (ie tugs)
What are the advantages of a Controllable Pitch Propeller (CPP)?
Better, faster control of speed
Much more manoeuvrability
More fuel efficient as the shaft does not need to be increased
Can apply astern propulsion almost instantaneously
What are the disadvantages of a Controllable Pitch Propeller (CPP)?
More complicated design therefore complex repair if a blade is damaged
When testing propulsion alongside the shaft is spun very fast which can lead to accidental full ahead / astern
More expensive than FPP
What is transverse thrust
When moving ahead through the water the helical discharge from the propeller, the speed of the water flow into the propeller disk, the form of the hull and the rudder all interact with each other and create additional forces.
What is squat?
Squat will affect a moving vessel in all states, that is, it does not matter whether the vessel is in deep water or in shallow water
Though the effect is most noticeable when the depth of water is less than twice the draught of the vessel
The restriction imposed at the bow causes the speed of water flow under the fore foot to increase
The increase in water flow creates a low pressure area under the fore foot which in turn leads to a loss
in buoyancy
This causes the bow to dip and creates both an even greater restriction to fluid flow and an increase in resistance to forward motion by a build up of water ahead of the vessel
What is the Bank effect?
A vessel navigating close to a gently shelving bank will experience forces pushing the bow away from and drawing the stern towards the bank
If the forces are strong enough, it may cause the vessel to roll towards the obstruction which because the draught has now increased on that side, may cause grounding on the low side
