Look through the listings on BoatTrader.com long enough and you’ll find a recreational boat fitted with a Cleaver-style propeller or a sleek nose cone on the leading edge of the stern drive. (For background, see Mercury Racing CNC Cleaver: Props for the Props.) The owner will tell you the boat is faster with that equipment. Hogwash. Here’s why.
Cleaver-style propellers work best on 100-plus-mph boats with surfacing drives, which means only half the propeller is in the water when the boat is at speed. For recreational boats with submerged drives, cleaver props are incredibly inefficient, particularly at low speeds and in reverse.
“Cleaver propellers supercavitate even if they’re submerged,” said Dr. Christopher Kent, assistant professor of ocean engineering at Florida Institute of Technology in Melbourne, Fla. “You don’t need to be up near the surface to have the entire suction back [front of the propeller] encapsulated in a bubble.”
That cavitation bubble makes for increased slip and vibration, which makes you go slower. Propeller designs for recreational boats have come a long way in the last 10 years. You’re much better off using a modern, stainless round-ear propeller, which can provide increased top speed without sacrificing efficiency.
Likewise, the rhetoric is that nose cones and lower gear cases with built-in nose cones—also known as crescent-leading-edge designs—increase a boat’s performance because of their sleek shape and sharp leading edge. Although it is true that a sharper leading edge can decrease drag, it’s also true that adding a nose cone can lengthen the gear case front to rear, which increases drag, thereby negating any benefits.
“If your boat doesn’t have the horsepower/hull combination to run in excess of 85 mph with the gear case it has, a CLE gear case will actually make it run a fair bit slower because of increased drag,” said Jack Litjens, Mercury Marine’s competitive intelligence manager. “This type of gear case is for a very specific application.”
So, if you are looking at a garden-variety runabout with those items on it, and the current owner claims it makes the boat faster, well, you’ll know better.