My notes on props which mostly came from:
https://www.vicprop.com/propeller101.htm
THRUST AND SLIP
High-speed runabouts and fast cruisers require relatively low thrust and therefore operate at low slip whereas tugs and other heavy vessels require high thrust and therefore operate most efficiently at high slip.
If the boat were tied to a dock, the propeller would not advance at all but would generate maximum thrust because full engine power would go into accelerating water astern. This would be called operation at 100% slip.
Slip must not be confused with efficiency that is a measure of the percentage of engine power converted to thrust by the propeller.
We have seen that we must have slip in order to generate thrust and the amount of slip will be proportional to the amount of thrust required by the boat.
Since force (thrust) is equal to mass times acceleration, it would seem that we might get the same force whether we gave a large acceleration to a small mass of water (small propeller turning fast), or a small acceleration to a large mass of water (large propeller turning slowly).
In practice, however, there are other factors such as the relation of the propeller pitch to its diameter and the energy losses due to friction between the accelerated water and the surrounding water that make a proper relation between boat speed and propeller shaft speed essential to an efficient installation.
make a proper relation between boat speed and propeller shaft speed essential to an efficient installation.
PITCH RATIO:
Pitch/Diameter(0.8-1.5)
In general, horsepower available and shaft speed determine the propeller diameter, while shaft speed and boat speed determines propeller pitch.
The pitch of a propeller divided by its diameter is a term called “pitch ratio.”
For best efficiency, the pitch ratio of boat propellers should be in the range of .55 to .80 for tugs and trawlers, .65 to 1.0 for heavy and avera