Not long ago, I bought a new Mercury for my Boston Whaler. When making this purchase, I learned that new motors don't come with propellers. Who would've guessed? Of course, the right propeller can have a noticeable effect on your engine's performance. Here's how to install or upgrade an engine propeller ' in this case, a stainless-steel Rapture XHS manufactured by Michigan Wheel Corp. ( www.miwheel.com ) and supplied by West Marine ( www.westmarine.com ).

STEP 1
The first step is to select the type of prop that is most conducive to how you use your boat. Most leisure boaters select an aluminum cast model, because they are relatively inexpensive and offer good all-around performance. Some shallow-water boaters use them, because if you hit an obstruction with a harder prop you can damage your shaft, even though the bushing within the propeller is designed to prevent this. Others choose composite props, which have replaceable blades ' reducing considerably the cost of repair. But most skinny-water boaters opt for a stainless-steel model, like the Rapture, because they offer the best performance. The downside is that they're more expensive than an aluminum or composite prop. Another important feature to consider is 'pitch.' The pitch, or angle, of the blades varies depending on the prop. A higher pitch will give you more speed, whereas a lower pitch will give you more torque. ('Torque' is the ability to get your boat 'out of the hole' from a dead stop.)

STEP 2
Next, remove the old prop from the foot of the motor. Generally, this is a fairly easy step. However, the age and condition of the engine will make a significant difference. This will be a little bit harder if the boat has not been dry-stored, and if there is corrosion and/or oxidation that has taken place in and around the foot of the motor. Using WD-40 or a similar marine lubricant product will certainly help. Before attempting to unscrew the large, visible nut that holds the prop in place, you will need to detach it from the part called the 'tab washer.' Almost every prop assembly utilizes a tab washer in order to keep the main nut tightly in place. It has small tabs around the outer edge that bend back into grooves in the drive shaft adapter. Using needlenose pliers, or a flathead screwdriver, you can bend these tabs forward, thus unlocking the nut. Once you've done this, you can then remove the nut with a floating prop wrench.

STEP 3
Most prop manufacturers suggest that you use a new hub kit to replace the prop, but unless the parts are worn, you can use the old ones to save money. This is one of the advantages of having this type of prop, as opposed to one that has the hub already pressed into it. If you need a new kit or are changing to a different kind of prop, make sure it's one designed for your particular brand of motor. The prop manufacturer usually has this kit available, if it's not already included with the prop kit itself. The hub kit is a collection of parts that hold the prop on the engine's shaft. It consists of something called a 'thrust washer,' urethane cushion hub, brass drive adapter, tub washer and a large, brass nut. Each of these parts is assembled in a specific order (as described in the last step) in order to securely hold the prop on the drive shaft. Installing the prop, along with the hub assembly, only takes a few minutes.

STEP 4
First, clean the shaft's splines and reapply a coating of quality marine grease. Then, place the thrust washer all the way onto the prop shaft. The washer should mate with and sit flush against the shaft taper. Insert the urethane cushion hub onto the prop hub cavity (at the forward end of the prop). Firmly press, or gently tap, the urethane cushion hub to secure it inside the prop hub cavity. Next, insert a part called the 'brass drive adapter' into the opposite end of the prop (aft end) to engage it in the slots in the urethane cushion hub. Do not over-tighten this nut ' make it just snug enough to keep the entire assembly firmly in place. Lastly, bend the tabs backward onto the tab washer with a flathead screwdriver, in order to lock the nut into place. Upgrading your prop can significantly change the performance of your boat, whether it's for an improved hole shot, to obtain a higher top speed, or even to improve your engine's rough-water capability.