The heavyweight model has a higher salt content and works great for fishing in the middle or bottom sections of the water column. The salt content varies based on bait size (8inch = 65% (41.0g), 6inch = 75% (17.0g), 5inch = 75% (11.3g) and placed near the bottom of the bait for better balance. The higher salt content causes the plastic to be more cloudy than the normal version. The keel is the secret for the unique jumping dirt action of Sakamata Shad. It allows the water to flow and creates a unique jumping action. It also acts as a rudder to create better darting action.