The engine feeds power through a vertical driveshaft (in the down housing or -midsection) to the lower unit, where you will find the anti-ventilation plate, cooling-water pickups, propeller and skeg. The lower unit also houses the water-pump assembly. Within the gear case, the drive train makes a 90-degree turn and becomes the prop shaft. In most outboards, forward and reverse gears are also located here, as is the exhaust exit.
Regular servicing of components within the lower unit helps ensure efficient and trouble-free delivery of power to the water. This includes removing the propeller every few trips to check for fishing line around the prop shaft. Left unattended, line can melt and cut into the prop-shaft seal, allowing water inside the gear case. If that happens, get the outboard to a service shop to replace the seal as soon as possible, as the water can quickly damage bearings and gears. Before re-installing the propeller, apply a generous coat of fresh marine grease.
Lube in the gear case should also be changed, per the recommended service intervals, with the appropriate oil. And finally, have the water-pump impeller and related parts replaced according to the service schedule.
Ultimately, it is the propeller that delivers power to the water. For maximum performance, make sure the prop is sized correctly and in good condition. Propellers are classified by diameter and pitch, as well as by material and number of blades. Pitch — a number that indicates the theoretical distance of travel (in inches) with each rotation of the prop — is the most important. Prop choice can vary widely, depending on the boat and motor combination, as well as how heavily or lightly the boat is loaded. As a rule, a prop should allow the engine to rev up to its maximum-rated rpm at wide-open throttle.
In multi-outboard setups, each engine might have a slightly different propeller. With twin outboards, for example, the gear cases usually rotate in opposite directions, requiring a right-handed rotation prop for one outboard, and a left-handed rotation for the other. The counterrotating -propellers nullify any prop torque, which otherwise can cause a boat to heel over at speed.
With three outboards, the center engine is often equipped with a four-blade prop, while the outside engines have three-blade models. The center outboard handles much of the work during acceleration, and four-blade props are better for this. In cruise mode, the outside engines shoulder the work, and three-blades are more efficient at these speeds.
Whatever prop you’re running, check the blades regularly for damage. Dings and missing chunks are easy to spot, but a slightly bent blade might not be readily apparent, though it often creates an odd vibration. Most damage requires the expertise of a prop shop for repair and rebalancing.
To prevent damage to the rest of the drive train, the hubs of outboard propellers are designed to give way if the prop strikes an object. However, hubs can also wear out with time and heat. So if your prop is 10 years old or older, it’s a good idea to have a prop shop check the hub.
A wise man once told me, “Take care of your equipment, and it will take care of you.” Apply this to your outboard, and it will power your fishing trips for years to come.