I wonder if it exists? I have seen the industrial sized jonboats, the kind often used for commercial pier construction and dredging barge operation and the like in various Texas bays and some in deep East Texas used on rivers like the Trinity for serious trot lining. The kind that have a big sides (gunwales?) that extend several feet above the water, not like the usual low riding jonboat that has 10 inches or so above the waterline.
I've seen these industrial jonboats with various types of canvas covers from half to full, to give the working men some shade. I even saw one boat a couple of years ago in Rockport dredging a harbor channel using a barge and running the barge from the jonboat. It had a great half cover over the back of the boat, looking like some kind of merchant boat you'd find on a big river in Africa or South America, where movies of those rivers have boats like these with partial or full covering or a roof, if you will.
There are lots of conventional boats that have either full or partial covers that shade the passenger compartment, and likewise larger sailboats have them as well. Lots of center console boats have bimini tops of various sizes. Problem is, usually you've got to have a boat of some substantialness to have a cover of any sort to withstand wind without blowing over a smaller craft. I've not conducted any trials but wouldn't think a canoe or a sit on top kayak would fair well with any type of cover, even a bimini style.
One of my more well heeled friends, the Judge, who is about to retire, just bought a trawler from up in the Northwest in Washington state or somewheres up that way. It's a HUGE boat, and has a downstairs cabin that sleeps 6 or so with a head and kitchen and such. He replaced the furnace that was built in the cabin with a huge air conditioner and moved the boat to Florida, where he plans to fish the Keys in this great craft, taking kayaks and perhaps a smaller boat towed behind.
In any event, he'll be cruising in air conditioned comfort when not fishing, or when needing a break from the sun.
Years ago down in Port Aransas, Texas, there was a now-defunct diving shop that rented these two seater catamaran kayaks for folks to take out in the bay and I suppose, ocean, and use as a diving base. They were big enough to hold a couple of tanks, and they had two seats SIDE BY SIDE. All of the kayaks you can find that hold two folks are those where you sit one behind the other.
There's a brand of catamaran kayak currently being made that is a solo one person craft but kind of resembles the one I rented for fishing in the the protected bays of the area. The one I rented was more substantial than the single person version I've seen, and would take up to a 5 hp outboard and had a high weight capacity.
That's the kind of craft I'd like to have, some kind of two seater craft with storage behind but where the occupants sit side by side, and have a folding cover not unlike those used on paddle boats that flips up and covers the passenger area for some shade action.
The older I get, the more I like having available shade when outdoors. When at the beach for any length of time, I generally erect a small tent, really a mini-cabana that can well shade two or three, that we got years ago for just such a purpose. On boats fishing, I generally have always tried to go very early in the morning or late in the evening into night time, all in an attempt to avoid getting too much sun and getting way to hot in these heatwaves we've been having for several years.
So I need to find a balance for a boat where I can affix some sort of sun covering/shade to provide some shade when out fishing in the brutal sun.