Work out propeller thrust (marine) instantly with clear inputs, formula shown and shareable results.
Thrust is useful power divided by speed: T = P x efficiency / V. That relationship explains why thrust is enormous at low speed and falls as the boat speeds up, and why bollard pull, measured at zero speed, must be estimated from a separate empirical relation rather than this formula.
Propeller thrust
T = shaft power x propulsive efficiency / boat speed (consistent SI units)
Marine results are planning estimates only. Verify against the vessel's approved stability booklet, loading manual, class society rules and applicable maritime regulations before loading or sailing.
Dividing by zero speed gives infinite thrust. At or near zero, momentum theory applies instead, giving thrust proportional to power to the two-thirds power.
Around 55-70% for a well-matched conventional propeller, lower for heavily loaded small props and higher for large slow-turning ones.