Choosing the correct marine gearbox damper plate requires checking several details relating to the engine, flywheel, gearbox and type of application.
The damper plate is installed between the engine flywheel and the gearbox input shaft. Its purpose is to absorb shocks and torsional irregularities, reducing noise, vibration and stress transmitted to the gearbox.
It should not be confused with a flexible shaft coupling, engine mounts or a cardan shaft.
The correct damper plate cannot be selected by diameter or spline count alone. Engine torque, flywheel mounting, spline profile and application details must also be checked.
Where Is the Damper Plate Installed?
The damper plate is bolted to the engine flywheel and connected to the splined input shaft of the marine gearbox.
In the power transmission system, it is therefore positioned between:
- engine;
- flywheel;
- damper plate;
- marine gearbox;
- propeller shaft or other propulsion system.
Because it is installed before the gearbox reduction ratio, it must be selected according to the torque produced by the engine.
What Is the Function of a Damper Plate?
An engine does not transmit perfectly uniform rotation.
Each combustion event produces an impulse that creates torque fluctuations in the crankshaft. These irregularities may be particularly noticeable:
- at idle;
- at low engine speed;
- when engaging gear;
- on diesel engines with a low number of cylinders;
- in applications with a lightweight flywheel;
- when play is present in the gearbox.
The damper plate helps reduce:
- gear rattle;
- shocks when engaging gear;
- torsional vibration;
- spline wear;
- stress on the marine gearbox.
Damper Plate and Flexible Coupling: What Is the Difference?
he two components have different functions.
Damper Plate
The damper plate is installed between the engine flywheel and the gearbox.
Its main purpose is to absorb torsional irregularities generated by the engine and help protect the gearbox.
Flexible Coupling
A flexible coupling is normally installed between the gearbox output flange and the propeller shaft.
It is used to reduce the transmission of vibration and, depending on the design, may compensate for small alignment errors.
A flexible coupling does not replace a damper plate, and a damper plate does not replace a flexible coupling.
What Is Torque in Nm?
One of the most important values when selecting a damper plate is engine torque.
Torque represents the rotational force transmitted by the engine and is measured in:
Newton metres – Nm
In simple terms, power indicates how much work an engine can perform over time, while torque expresses the rotational force available at the shaft.
How Is Torque Calculated?
When the engine power in kW and the corresponding engine speed are known, theoretical torque can be calculated using:
Torque (Nm) = 9550 × Power (kW) ÷ Engine speed (rpm)
9550 × 100 ÷ 2500 = 382 Nm
Example
Engine data:
- power: 100 kW;
- speed: 2,500 rpm
The theoretical torque at that engine speed is therefore:
7024 × 150 ÷ 3000 = 351 Nm
382 Nm
Calculation from Metric Horsepower
When the power is stated in metric horsepower:
Torque (Nm) = 7024 × Power (CV) ÷ Engine speed (rpm)
Example:
- power: 150 CV;
- speed: 3,000 rpm.
7024 × 150 ÷ 3000 = 351 Nm
The theoretical torque is therefore approximately:
351 Nm
Whenever possible, it is preferable to use kW, especially when it is not clear whether the stated power is in CV or HP.
Which Engine Speed Should Be Used?
This is one of the most important points.
A calculation based on maximum power and maximum engine speed gives the torque produced at that specific operating point, but not necessarily the maximum torque of the engine.
For example:
- maximum power: 100 kW at 3,000 rpm;
- calculated torque: 318 Nm;
- maximum torque declared by the engine manufacturer: 400 Nm at 1,800 rpm.
For damper plate selection, when available, it is therefore preferable to use:
the maximum torque declared by the engine manufacturer and the corresponding engine speed.
The formula is useful when this information is unavailable, but it does not replace the engine torque curve
Does the Gearbox Reduction Ratio Change the Damper Plate Torque?
No, not for a damper plate installed between the engine and the gearbox.
The damper plate is located on the input side, before the reduction ratio. It must therefore be selected according to the torque produced by the engine.
The reduction ratio increases the torque available at the gearbox output, less mechanical losses.
Nominal Torque and Maximum Torque
Damper plate specifications may show different torque values.
Nominal Torque
This is the torque the damper plate can transmit during normal continuous operation.
It may also be described as:
- nominal torque;
- rated torque;
- continuous torque.
Maximum Torque
This is the higher value the component can withstand for short periods or under transient conditions.
It may also be described as:
- maximum torque;
- peak torque;
- transient torque.
Maximum torque must not be treated as the normal continuous operating capacity.
Why Torque Alone Is Not Sufficient
A damper plate should not be selected solely by checking that its nominal torque is higher than the calculated engine torque.
Other factors must also be considered:
- number and arrangement of cylinders;
- diesel or petrol engine;
- idle speed;
- torsional irregularities;
- flywheel mass;
- gearbox type;
- frequency of gear engagement;
- vessel type;
- leisure, commercial or continuous-duty use;
- elastic characteristics of the damper plate.
A diesel engine with a low number of cylinders may generate stronger torsional impulses than an engine with more cylinders, even when power and nominal torque are similar.
The torque calculation provides a reference value. Final selection must comply with the limits and criteria specified by the damper plate manufacturer.
What Information Is Required to Select a Damper Plate for a Marine Gearbox?
To identify the correct component, details of the engine, gearbox and existing damper plate are required.
Engine Details
- manufacturer and complete model;
- power in kW, CV or HP;
- engine speed corresponding to the stated power;
- maximum torque in Nm, when available;
- engine speed at maximum torque;
- number and arrangement of cylinders;
- type of vessel operation.
Gearbox Details
- manufacturer;
- complete model;
- version;
- input shaft spline profile;
- shaft diameter;
- number of splines;
- manufacturer’s part number, when available.
Damper Plate Details
- outside diameter;
- number of mounting holes;
- hole diameter;
- hole spacing or pitch circle diameter;
- centring diameter;
- overall depth;
- hub projection;
- stamped part number, when available;
- clear front and side photographs.
How to Identify the Spline Profile
The spline profile must match the gearbox input shaft exactly.
Knowing only the number of splines is not sufficient.
The following should be checked:
- outside diameter;
- root diameter;
- number of splines;
- tooth form;
- pitch;
- usable length;
- applicable spline standard.
Two shafts with the same number of splines may have different diameters or tooth profiles and may not be compatible.
How to Check the Flywheel Mounting
The damper plate must also match the flywheel drilling pattern.
Check:
- number of holes;
- hole diameter;
- hole spacing;
- pitch circle diameter;
- centring diameter;
- available space inside the bell housing.
A plate with a similar outside diameter may have a completely different mounting pattern.
Measurement Legend
- D = flywheel outside diameter
- d = pitch circle diameter of the mounting holes
- Ø holes = diameter of the mounting holes
Measurements should be taken accurately, preferably in millimetres. The outside diameter alone is not sufficient to identify the correct damper plate.
Signs of a Worn Damper Plate
Common symptoms may include:
- metallic noise at idle;
- shocks when engaging gear;
- unusual vibration;
- excessive play between engine and gearbox;
- fragments or debris inside the bell housing;
- spline wear;
- irregular torque transmission.
These symptoms do not automatically prove that the damper plate is faulty.
Noise and vibration may also be caused by:
- idle speed set too low;
- worn engine mounts;
- incorrect alignment;
- internal gearbox play;
- propeller shaft problems;
- damaged propeller;
- irregular engine combustion.
The complete system should therefore be inspected before replacing the damper plate.
Common Mistakes to Avoid
Do not select a damper plate based only on:
- outside diameter;
- number of springs;
- colour;
- visual similarity;
- gearbox model alone;
- engine power alone;
- number of splines;
- incomplete part number.
Two apparently similar components may have different torque capacity, stiffness, depth, mounting pattern or spline profile.
Example of a marine gearbox damper plate.
How to Request a Check from Scandiesel
Unsure Which Damper Plate You Need?
Please send us:
- engine model;
- power and engine speed;
- maximum torque, when available;
- gearbox model;
- damper plate dimensions;
- spline details;
- photographs of the component.
We will check the available information to identify a solution compatible with the engine, gearbox and type of application.