What is the difference between thru-hub exhaust, over-hub exhaust, and non thru-hub
exhaust?
Thru-hub exhaust propellers consist of a round barrel to which
the blades are attached. The exhaust passes through the barrel and out the back,
without making contact with the propeller blades. This provides provides a good
clean water flow to the blades, usually resulting in good acceleration and hole
shot.
Over-hub exhaust propellers have the blades attached directly to
the smaller tube that fits over the propeller shaft, eliminating the larger exhaust
tube. These types of propellers are often used for attaining maximum top speeds.
(On some boats, the hole shot can often suffer due to the extreme exhaust flooding
that occurs around the propeller blades during acceleration.)
Thru-hub exhaust and over-hub exhaust propellers
are used on boats where the exhaust passes out though the rear of the “torpedo”
on the lower unit, around the propeller shaft. Most outboards utilize this type
of exhaust.
Over/Thru-hub exhaust propellers are a combination of thru-hub
and over-hub exhaust propellers. This allows some exhaust to escape at lower RPMS,
providing a controlled amount of exhaust flooding. These types of propellers will
allow the propeller to be slightly easier to turn during initial acceleration, allowing
for a better hole shot on some engine/boat combinations.
Non thru-hub exhaust propellers are used for inboards using shaft
driven propellers, sterndrives using through hull exhaust, and on some outboards
that don’t route the exhaust through the lower unit torpedo.