Even an absolute newcomer to the sport of pleasure boating begins with a basic understanding of engine exhaust, but it may come as a surprise to some that outboard boat props actually have several ways of releasing or venting the exhaust produced by the motor.  One of the most common arrangements is through “hub exhaust.”  These propellers have blades attached to a hollow barrel through which exhaust can pass.  This allows exhaust to avoid contacting the blades directly, which improves the way water flows onto the blades.

Another arrangement is “non-through hub exhaust.”  As one might expect, in this system there are not any holes for exhaust near the shaft of the propeller.  These systems are most commonly found on stern drive motors with low horsepower and on some low horsepower outboard motors.

Still other outboard propellers use a system known as “over the hub exhaust.”  In this arrangement, blades are directly affixed to a small tube that runs near the propeller shaft.  This eliminates a large exhaust tube.  Over the hub exhaust systems are often employed when boating enthusiasts want to reach the maximum possible top speed of their motor.

The final system commonly employed is termed “over/through hub exhaust.”  This is a combination arrangement that uses features from both the over-hub and through-hub systems.

Since outboard props can use a variety of exhaust systems, the boater determined to get superior performance should carefully consider which system would best suit his watercraft and his needs.

Tags: Outboard Propellers, propeller terminology

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