Definitions - GB, Propeller, Shaftline Flashcards
What is the necessity of having a gearbox
A gearbox can reduce or increase the speed of a driven gear
Gearbox reduction
Occurs when the drive gear is smaller or has fewer teeth than the driven gear
Gearbox overdrive
Occurs when the drive gear is larger or has more teeth than the driven gear, therefore output speed will be faster than input
Propeller pitch
The distance the propeller would “drive forward” for each full rotation
RPM
Revolutions per minute, the numer of full rotations of a propeller in a minute
Slip
The difference between the normal pitch and the actual distance travelled by the vessel in one rotation
Cavitation
Rapid changes of pressure in a liquid that leads tp the formation of small vapor-filled cavity with low pressure, measured in PSI
Clearance
Needs to be enough space to prevent vibrations and have a good performance
Fixed pitch
Angle of attack of the blade does not change
Controllable pitch
The angle of attack can be changed which allows for different loads but can create more drag due to a bigger boss
Contrarotating
Two propellers on the same shaft that spin opposite ways, this allows for a reduction in diameter but needs a contrarotating shaft system
Feathering
Can have a constant thrust in any wave condition but is expensive
Folding
Low drag in sailing conditions but poor performance in reverse
What is a shaftline
A shaftline is a shaft that connects to the gearbox and allows the propeller to turn
Taper connection
Usually used on straight shafts
