Mercury - Performance Vent System Plug Propeller Vent Plug Composite 889725047. Overview. If you've ever fine-tuned your boat's holeshot or chased that perfect balance of lift and grip, you know the smallest adjustments can make the biggest difference. The Mercury 889725047 Performance Vent System Plug gives you that control - a simple piece, but one that lets your propeller respond the way you want it to. It's the kind of part you appreciate after a long weekend on the water, when you realize y