The ZF Marine power shifting, 2-Speed concept covers a range from around 300 hp to 1100 hp, intended principally for Pleasure and Light Duty applications, however ratings for Medium and Continuous Duty are available on request.

The majority of these transmissions are designed with a separate input stage, which may be planetary or parallel gear design, depending on the model. For the larger transmissions (series ZF 350 TS and ZF 550 TS) the gap between 1st and 2nd speeds can be varied in a range from approx. 10 to 30 %, by selecting one of the available ratios. In the case of the ZF 312 TS, which has an integral 2-Speed arrangement (no input stage), any 1st speed ratio can be matched to any of the 2nd speed ratios.

The optimum gap between 1st and 2nd speed will depend on each specific application. Parameters influencing this choice could be:

  • Hull design
  • Displacement
  • Longitudinal Centre of Gravity (LCG)
  • Total installed power
  • Propeller design
  • Operating profile (in particular, the requirement for higher acceleration and/or higher maximum speed).

IMPORTANT ! For every 2-Speed application, the propeller must be designed for the maximum boat speed when using the 2nd gear ratio . The optimum gear ratio combination must be confirmed after consultation with ZF Marine's technical department.

The higher ratio of the 1st speed permits higher acceleration and reduces the load on the engine. Manoeuvring in confined waters is also easier and the boat can be operated more safely in heavy sea conditions.

Optimised Choice of Ratios

The greatest benefit of the 2-Speed concept can be obtained by combining the advantages of improved acceleration, manoeuvring etc. with an increase in maximum boat speed.

If a large ratio gap is chosen, which covers the gear ratio normally selected for a conventional, single-speed installation, you have the optimum advantages. For instance, for a boat normally using ratio 1.524:1 as the best compromise between performance and ability to get on the plane, you can now optimise the acceleration by selecting a 2-Speed transmission with 1st ratio 1.778:1 and 2nd ratio 1.445 (or even 1.344) to give a higher boat speed.