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Flexible shaft couplings and shaft flanges for a boat's propeller shaft

Flexible axle clutches

VETUS offers a wide range of solutions for connecting the propeller shaft to the engine. The flexible rubber element in the shaft coupler ensures quiet and vibration-free power transmission and reduces the load on the engine caused by the propeller shaft.

For smaller axles up to Ø 30 mm, you can choose between the Bullflex, Combiflex, Uniflex13, or KO5 models. For larger axles, up to Ø 70 mm, the options are the Bullflex and Uniflex16 models.

What is a flexible shaft coupling?

A flexible shaft coupling for a boat, also known as a flexible flange or flexible coupling, is a mounting flange installed between the engine gearbox and the propeller shaft that transmits engine power to the propeller shaft; it features a vibration damper that reduces resonance.

Its purpose is to dampen the vibration, noise, and shocks caused by the engine and propeller shaft, making boating quieter, more comfortable, and at the same time protects the drivetrain components by reducing the stress placed on the drivetrain.

How should a flexible shaft coupling be selected?

The Vetus flexible coupling is selected based on the engine power, the reduction gear ratio, the propeller shaft diameter, and the engine transmission. The flexible coupling must be able to withstand the engine’s maximum torque and accommodate any minor misalignment.

The correct flexible coupling is selected by calculating the force transmitted from the gearbox to the propeller shaft in kW/100 rpm.

  1. ✔ Calculate the propeller shaft RPM: maximum engine RPM ÷ gear ratio
  2. ✔ Divide by 100
  3. ✔ The transmitted power is the engine power (kW) ÷ the shaft speed calculated in the previous section / 100 rpm
      • ✔ For example, an engine with a power output of 84 kW at a maximum speed of 3,600 rpm and a marine gearbox reduction ratio of 2.1:1.
        The propeller shaft speed is 3,600 ÷ 2.1 = 1,714 rpm
      • ✔ 1714 ÷ 100 = 17.14 kW / 100 rpm.
      • ✔ The transmitted power per 100 rpm is 84 kW ÷ 17.14 = 4.9 kW/100 rpm.

The power rating of a Vetus flexible coupling is specified in relation to the rotational speed, e.g., a certain power (kW) per 100 revolutions. Make sure the coupling can handle your engine’s torque and rotational speeds. For example, Bullflex series clutches can withstand even strong impacts, while Uniflex models can compensate for angular misalignments of up to 2°.

Vetus Bullflex: An excellent choice when the best possible vibration and noise damping is required. Particularly suitable for soft engine rubber mounts.

Vetus Uniflex: A highly precise and stable coupling that allows for an angular misalignment of up to two degrees (2°) between the motor and the shaft.

Vetus Combiflex: A more compact option, suitable for situations where space is limited but the drivetrain requires a little flexibility.