Before you buy an outboard motor for your fishing boat, runabout or dinghy, make sure to buy the correct shaft length.
First measure the boat's transom height from the top of the transom (motor mount) to the bottom of the boat (usually the bottom of the transom, but not always).
With the correct shaft length on an outboard motor, this distance should match from the inside of the engine mounting bracket to the bottom of the cavitation plate, just above the propellor. That makes sense, since once the motor is fastened to the transom, the prop will just extend in water below the boat's maximum depth. These are recommended lengths.
| Transom ht. inches | Centimetres | Shaft length inches | Centimetres |
| 14 - 17 ¼ | 36 - 44 | 15 (short) | 38 |
| 17 ¼ - 19 ½ | 44 - 50 | ||
| 19 ½ - 22 ½ | 50 - 57 | 20 (long) | 51 |
| 22 ½ - 27 | 57 - 69 | 25 (extra long) | 64 |
You should use oil made by the company that manufacturer of the engine. It may cost more than generic oils, but can help your expensive motor last longer.
