We have a hardtop now, and our previous boat had one, too... and I don't think I'd ever want a big boat again without one. But both of these boats were expected to/designed with hardtops from the git-go.
Some benefits (you'll know this):
- Provides decent shade
- Provides real estate for mounting sensors, antennas, radars, etc. and presumably solar panels, given enough space.
- And on the underside, it offers a place for overhead electonics components (radios, fishfinders, radar displays, whatever) and also for some overhead lights, spreader lights, etc.
- Provides a hanger system for enclosure panels, and if some of those panel openings are not of the "roll-up" variety it also provides an easy way to "pin up" open panels, especially rigid panels like Makrolon/EZ2CY/etc.
- On our previous boat, an express sportfish, we could hoist our (upside down) inflatable up there
- In winter locations, it handles snow load relatively well
Some of that could have been solved using the exoskeleton approach; radars and so forth can instead be mounted on aluminum or stainless pipe that forms a support structure for some hardtops (Atlantic Towers products, for example)
There's a boat in the marina near us with that very lightweight "hardtop" material mounted to a bimini or exoskeleton. I forget the brand name. Looks like it'll do SOME of that stuff, but it also looks like it's not all that great for directly mounting heavy components (like a radar array). Looks "aftermarket" -- more so than the Atlantic Towers examples, which I'd guess are significantly more expensive.
FWIW, we have our full enclosure in two major parts, fore and aft. (Duh!) The forward part is 5 panels; the center 3 are Makrolon polycarbonate "glass like windows" (center segment pins up to the hard top when open), and the two sides are Regalite something or other sheet vinyl with zip open "smilies". Would have gone with pin-up versions there, too, but other bits and pieces (support frame, electronics box, etc.) prevented.
The after part is 5 panels of Regalite, all 5 with roll-up "smilies." All 5 usually removed and stored during our late spring/summer/early fall months.
All the Sunbrella pieces are sewn with Tenera thread, with heavy/straight YKK connecting the panels, and coil zippers for all the "smilies," and with connecting zippers overlayed with extra Sunbrella closed over the zippers with hook-and-eye seals. I know the forward segment has withstood an 80 MPH straight line "Derecho" wind, just after it was installed (and before the after part was fitted). In colder weather the enclosure makes a decent greenhouse (it was 22°F when we left Myrtle Beach last January en route Charleston, bearable at least on the bridge), and at least it's almost completely dry on the bridge.
Stratoglass is another sheet vinyl product; our original was made with that. I haven't noticed much difference between that and the Regalite.
-Chris