Originally Posted by Airpacker (Post 3254227)

You mean like this?

http://www.offshoreonly.com/forums/a...bh-drive1.jpeg

This is one I did on my old black hawk drive. It allowed a stock 500efi to plane off with twin 31 pitch props. Without the airation tube, the boat would not plane with anymore than two passengers and NO fuel load. With it, planing with full fuel and 6 onboard was easy.

Originally Posted by Airpacker (Post 3254221)

yes, no and kind of.....

The tube in question is known as an airation tube. It allows the propeller to suck air from the surface which causes the prop to lose its "bite" in the water and slip. This allows the engine to rev up into its torque curve and roll the boat over onto plane without lugging.

Most of the big HP surface drive boats turn very big props meant to run with barely half a prop in the water. It takes big torque to turn them when fully submerged ( off plane ) "Airating" the props takes a large amount of load off the drivetrain when the props are still fully submerged.

Think of it as slipping the clutch to take off in a standard trans car in 5th gear. Once your rolling along at highway speed, the car has plenty of power to accelerrate.