The only time we have an issue with this submarining is if we tow it empty too close to the outboard (moving from one area to another). Otherwise, it's been perfect towing our 5-year-old by himself or with my wife, and a bunch of friends.
Couple suggestions: 1. Use the ski bar if your boat has one, 2. Make sure passengers stay towards back of tube, 3. Make sure the quick connect goes through the strap on bottom before connecting to rope, and 4. Keep the tube inflated to where it's hard.
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