Sportsstuff Rampage Halfpipe water ski tube water towable is great fun for two!  Dimension is 72" diameter. 
Model 53-2155

Features:

• Double-Webbing Foam Handles with Knuckle Pads
• Double-Stitched Nylon Full Cover with zipper
• P.U. Fabric Coating
• Heavy-Gauge PVC Bladder
• Speed Safety Valve
• Self-Bailing Drain Vent
• Reinforced Tow Systems

Product SKU: 72-4589