Selection of gearbox units

The right choice of engine revolutions transmission is another key element from the point of view of performance and drive effectiveness. The following elements have an influence on transmission:

  • engine revolutions (rpm)
  • power to weight in tonnes ratio (hp/t)
  • speed of advance or  Froude coefficient (V/LWL0,5)


V – speed in kn
LWL – waterline length (in feet)
P – total power of drive units
W – total weight in tonnes
RPM – engine revolution speed

Assuming that  V/LWL0,5 coefficient is higher than 1 and the total power is higher than 100, the following formula may be applied:

R= 1,45 x exp((0,0034xT))

Where T=RPM/P/W

There are several significant gearbox providers  – the most renowned one is the German ZF, and Kanzaki, a slightly cheaper manufacturer cooperating with Janmar.