Propeller Size Calculator for
Planing Hulls

Enter waterline length of vessel
in feet
Enter beam at the waterline
in feet
Enter hull draft
in feet
Enter vessel weight
in pounds
Enter number of engines (shaft lines)
(max 2)
Enter maximum rated horsepower (per engine)
hp
Enter maximum rated engine RPM
RPM
Enter gear ratio
:1
Enter number of shaft bearings
per shaft
Enter Constant "C"
(based on table below)
Type of Boat:
Average runabouts, & cruisers
High speed runabouts, very high speed cruisers
Race type boats
C =
150
190
210
Enter Desired maximum speed
Knots

Intructions

This calculator is free to use as often as you wish.
The calculations and results are based on imperical data and formulas.
The results are only as acurate as the data you enter.
The calculated propeller sizes are based on standard propeller designs;
2 blade = 30% blade area ratio
3 blade = 50% blade area ratio
4 blade = 69% blade area ratio
What it will do

Calculate a propeller size based on the data you enter
Calculate a vessel speed based on the available horsepower
Calculate the horsepower required for a desired speed

What it won't do

No calculations for cavitation
No calculations for blade area ratio
No calculations for towing, bollard thrust, etc.