2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 296Get this manual
4DRIVE LOWER UNIT 1) LONG ANTI-CAVITATION PLATE
Compared with previous F15 (66M), the anti-cavitation plate has been extendedThis could prevent air-drowning while drivingBesides, it can obtain the stability of engine storage when its rear faces down as the fin of trim tab is not out of the anti-cavitation plate end(No contacts the trim tab to the ground) Adjustable trim tab is used, and its mount portion is buried into the anti-cavitation plate