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 marine 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 1 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
Heavy Duty Coupling
Couplings for the gearbox are flanged. The couplings come in a variety of shapes and sizes. A variety of methods can be used to attach to the propeller shaft.
Traditionally, the propeller shaft has taper at both ends. The taper would allow the coupling to be machined at the same time as the propeller shaft. This is a common system when high loads and heavy vessels are involved. A worn out propeller shaft can be machined. This allows the propeller shaft to be reused.
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| Illustration 5 | g00744685 |
Heavy duty coupling arrangement (1) Dowel pin (2) Clamping bolt (3) Key (4) Propeller shaft (5) Gearbox output flange (6) Nut for the clamping bolt | |
Illustration 5 represents an alternative method. The propeller shaft is fastened by a split coupling. A key provides a positive drive. A dowel pin is used in the propeller shaft in order to eliminate the possibility of being pulled out of the coupling. This system is intended for Twin Disc marine gear.
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| Illustration 6 | g00744684 |
Dimensions for the heavy duty coupling Refer to Table 1 for the dimensions. | |
| Dimensions for the Heavy Duty Coupling Refer to Illustration 6. |
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| A | 86.4 mm (3.40 inch) |
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| B | 76.2 mm (3.00 inch) |
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| C | 146.1 mm (5.75 inch) |
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| D | 79.3 mm (3.12 inch) |
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| E | 28.5 mm (1.12 inch) |
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| F | 108.0 mm (4.25 inch) |
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| G | 31.8 mm (1.25 inch) |
35.1 mm (1.38 inch) |
38.1 mm (1.50 inch) |
44.5 mm (1.75 inch) |
50.8 mm (2.00 inch) |
| H | 7.9 mm (0.31 inch) |
7.9 mm (0.31 inch) |
9.7 mm (0.38 inch) |
11.2 mm (0.44 inch) |
12.7 mm (0.50 inch) |
| I | 35.3 mm (1.39 inch) |
38.6 mm (1.52 inch) |
42.4 mm (1.67 inch) |
49.5 mm (1.95 inch) |
56.6 mm (2.23 inch) |
| J | 120.9 mm (4.76 inch) |
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| K | 15/32 inch Drill Ream 0.4990 to 0.5005 inch |
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| L | 3.43 mm (0.135 inch) maximum width |
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The heavy duty coupling must be machined. The procedure follows:
- Bore the coupling to the desired shaft diameter (G) .
- A keyway must be broached to the respective dimension (H). The keyway must be 101.6 mm (4.00 inch) long.
- Clamp the coupling to the propeller shaft in the position. Refer to Illustration 5 for the correct position.
- Drill 15/32 inch hole through the propeller shaft. Refer to callout (K) in Illustration 6 for the location.
- Ream 0.4990 to 0.5005 inch through the coupling and the shaft
- Remove the coupling. Clean the propeller shaft and the coupling. Install the coupling. Install the dowel pin. Refer to Illustration 5.
Light Duty Coupling
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| Illustration 7 | g00744862 |
Light duty coupling arrangement (7) Output shaft (8) Key (9) Propeller shaft (10) The propeller shaft should be pressed against the output shaft. (11) Set screw | |
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| Illustration 8 | g00744861 |
Dimensions for the light duty coupling Refer to Table 2 for the dimensions. | |
| Dimensions for the Light Duty Coupling Refer to Illustration 8. |
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| M | 9.53 mm (0.375 inch) (1) |
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| N | 80.3 mm (3.16 inch) |
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| P | 63.5 mm (2.50 inch) |
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| Q | 127.0 mm (5.00 inch) |
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| R | 9.7 mm (0.38 inch) |
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| S | 22.4 mm (0.88 inch) |
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| T | 54.9 mm (2.16 inch) |
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| W | 25.4 mm (1.00 inch) |
28.5 mm (1.12 inch) |
31.8 mm (1.25 inch) |
35.1 mm (1.38 inch) |
38.1 mm (1.50 inch) |
44.5 mm (1.75 inch) |
50.8000 mm (2.00 inch) |
57.6 mm (2.25 inch) |
| X | 6.35 mm (0.250 inch) |
6.35 mm (0.250 inch) |
7.87 mm (0.310 inch) |
7.87 mm (0.310 inch) |
9.65 mm (0.380 inch) |
11.18 mm (0.440 inch) |
12.70 mm (0.500 inch) |
14.20 mm (0.560 inch) |
| Y | 28.5 mm (1.12 inch) |
31.5 mm (1.24 inch) |
35.3 mm (1.39 inch) |
38.6 mm (1.52 inch) |
42.4 mm (1.67 inch) |
49.5 mm (1.95 inch) |
56.6 mm (2.23 inch) |
63.5 mm (2.50 inch) |
| Z | 108.0 mm (4.25 inch) |
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| ( 1 ) | UNC thread |
Refer to Illustration 7 for the light duty coupling arrangement. Forward thrust is applied directly to the gearbox output shaft. The propeller shaft is pressed against the gearbox output shaft. The propeller shaft is secured by two set screws. Positive drive is provided by a key.