Propeller Shafts
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| Illustration 1 | g00744539 |
Typical propeller shaft and coupling installation (1) Level of the sea water (2) Flexible mounted seal for the propeller shaft (3) Cutless bearing (4) Flexible coupling for the propeller shaft (5) Flexible engine mounts | |
The engine should be mounted on flexible engine mounts. The flexible engine mounts reduce the transmission of noise and vibration to the hull of the vessel.
The OEM is responsible for the design of the propeller shaft and the type of propeller shaft that is used. The systems that are currently active are shown.
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| Illustration 2 | g00744537 |
One type of seal for the flexible mounted propeller shaft (6) Propeller shaft (7) Stuffing box (8) Graphite string (9) Reinforced rubber hose | |
Illustration 2 shows one type of seal for the flexible mounted propeller shaft. This type of seal is used when the propeller shaft is supported by the coupling for the gearbox and supported by an outboard bearing that is made of rubber. The support is at the propeller end of the propeller shaft. A seal prevents water from entering the hull. The seal for the propeller shaft must be flexible in order to allow movement of the engine. A flexible coupling for the propeller shaft is mounted to the coupling for the gearbox. This allows momentary angular misalignment in operation.
Refer to Illustration 2. The following items must not create a whirling motion:
- Speed of the propeller shaft
- Diameter of the propeller shaft
- Unsupported length of the propeller shaft
Whirling is the centrifugal force that is generated by the speed of rotation. Whirling will cause the propeller shaft to bow.
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| Illustration 3 | g00744538 |
Another type of flexible seal for the propeller shaft (10) Sterntube (11) Oil reservoir (12) Rubber molding (13) Propeller shaft | |
Use the arrangement that is shown in Illustration 4 when the length of the propeller shaft can not be supported by the coupling for the gearbox and the outboard bearing.
With this arrangement, one or more additional bearings are mounted on the propeller shaft. The coupling for the propeller shaft should be flexible. This will allow the engine to move on the flexible engine mounts.
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| Illustration 4 | g00744664 |
Alternative arrangement for the propeller shaft (14) A siphon break is needed when a water lift exhaust system is specified. Refer to Installation Guide, "Exhaust Systems" for more information. (15) A water supply for the bearings is needed. Install a hose from the 1/4 inch BSP tapping on the end cap for the heat exchanger. (16) Level of the sea water (17) Flexible engine mounts (18) Flexible propeller shaft couplings (19) Bearings for the propeller shaft | |
There is an alternative arrangement for the propeller shaft for this type of installation. A thrust block is needed for the propeller shaft. The thrust block should be installed as the propeller shaft enters the engine room. A constant velocity joint is installed at each end of the propeller shaft. The constant velocity joint is connected to the propeller shaft before the coupling for the gearbox. Refer to Illustration 4.
Couplings
Flanged Propeller Shaft Couplings
Flanged propeller shaft couplings can be supplied with any marine transmission. The couplings must be machined in order to suit the propeller shaft. Use the following procedure for machining the coupling and the propeller shaft:
- Machine the end of the propeller shaft in order to reduce the diameter. The diameter should be reduced by 2 mm (0.0787 inch) over a length that will suit the coupling. Machine a keyway in the propeller shaft.
- Bore the coupling in order to fit the propeller shaft. Machine the coupling in order to suit the key.
- Assemble the coupling and the propeller shaft with the key. Ensure that the propeller shaft is fully installed.
- Drill a 6.35 mm (0.250 inch) hole into the coupling. The hole should extend into the propeller shaft by 2 mm (0.0787 inch).
- Remove the propeller shaft from the coupling. Bore the hole in the coupling to 8 mm (0.3150 inch). Tap the hole to 9.5250 mm (0.375 inch). Clean the bore of the coupling.
- Reassemble the propeller shaft to the coupling. Install a 9.5250 mm (0.375 inch) setscrew. The setscrew locks the coupling to the propeller shaft.
Alternative Arrangements
There are alternative methods for locking the coupling to the propeller shaft:
- Drill through the hub of the coupling and the propeller shaft. Install double roll pins.
- Use a washer that is secured by a bolt. The bolt is threaded into the end of the propeller shaft. The coupling will require machining to accommodate these components. The engagement of the propeller shaft within the coupling will require adjustment.
Clamp Type Couplings
Some propeller shafts are supplied with excess length. In this case, a clamp type coupling should be used. It is not necessary to machine a shoulder on the end of the propeller shaft. The propeller shaft should be locked to the coupling. Refer to "Alternative Arrangements" for information about locking the propeller shaft to the coupling.
Flexible Couplings
A flexible coupling may be used. However, the propeller shaft should not be continuously out of alignment. A momentary deflection of the propeller shaft is acceptable with a flexible coupling. The flexible coupling is between the transmission output flange and the coupling for the propeller shaft.