Here's my experience from the kayak. If you covered 7 miles, you'd be exhausted. If you did nothing but paddle all day, you'd get about 10 miles, unless it was glass calm. While 4-5 mph is possible it's not sustainable for distance paddling, you end up averaging more like 1.5-2MPH by yourself anyway. My Hobie has a sail kit available, I just think it'd get in the way, the best thing about the Hobie and Kayaks like Native Propels are the "peddle" drive systems, if you were gonna do anything to improve your distance, I'd suggest looking into something that would give you "leg" power rather then oars. Maybe retro fit from a paddle boat or something.
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