You would need to go slow until you found out if there were any submerged sticks and such, but if it's a clean lake it should be ok.

As for the sleigh ride, a small boat is a disadvantage in catching large fish. The reel drag takes care of the strain and the boat becomes a towed weight for the fish, but the worst part with a Blue Marlin would be the end game when the fish is close to the boat and you have the bill to contend with - particularly if the fish is aggressive and/or jumping. It would certainly be a Chinese fire drill with anything other than a dead fish. I've found an ice pick to the brain works well, but sometimes you can miss that pea size brain and all Hell breaks loose.... wouldn't be any fun on an inflatable with gaff hooks flying around.... still, I'd like to try it.

Frank