The seats built into the sternrail should certainly be able to handle a couple hundred pounds, although it might be assumed that the geometry of the railing was configured to account for that load.
I have no definitive answer to whether 81 pounds higher up on the rail is appropriate, but would I do it on my boat? No. It may be fine, but I'd err on the side of no.
And as the previous reply said, wrestling that amount of weight could be rough. One thing on dry land, but with objects in water with limited space in which to maneuver.....I'll pass. Aside from losing it overboard, I'd be concerned about dinging the gelcoat with that much mass swinging around. Slip while you're holding 81 pounds in your arms like a baby and stop yourself with your chin on the bottom rail. Uh uh:naughty:.
I recently got a nice 10' Avon inflatable rated for 10 horse, for free, and I was itching to get a used 10 for it so I could blast around in it. In the end, I decided it's just not practical. A four horse is waaaay easier to deal with, with the downside being you don't get to plane off.
After saying all that, I'm sure there are plenty of folks out there with similar boats that have 81 pounds on the rail with no casualties.
