We have went as high as three stacked. Bottom and top boat had frame, middle one didn't. Smaller boat in middle that fit between oar towers. Worked OK. Biggest issue is boats losing, gaining air, straps come lose, or get VERY tight. Nice to have boats inflated at launch, though. We tied each boat seperately to trailer, but still had issues with top boat. Used a little carpet between where we thought wear would be an issue. Just two boats shouldn't be too as bad.