The easiest way to move the speedometer needle is to switch propellers. For a runabout-style V-bottom equipped with an aluminum prop, replacing the prop with a stainless-steel model will usually yield a gain of about 2 to 3 mph. Because stainless steel is stronger than aluminum, the propeller blades don’t flex, and the blades are thinner, which lets them cut through the water with less resistance. Mercury’s Enertia prop is made of an alloy that’s stronger than stainless steel. When I switched from a stainless-steel prop to the same size Enertia on my 23-foot Chaparral bowrider powered by a MerCruiser 350 Mag MPI Alpha One, I picked up two more miles per hour, so going from a stock aluminum prop to the Enertia could gain you up to 5 mph in additional speed.