As noted, even the bare poles are subject to wind. A ship aground is already being buffeted by the waves, add to that continued pressure from the masts (with the lever action they exert on the hull because it cannot move) and you get a serious strain on the hull.
Yep, I just calculated hull speed to get that number. While I certainly agree that there is no guarentee that the Suprise could achieve that speed, I’d find it, err, suprising if a british frigate wasn’t a fast ship. I’d guess that she’d get close. And I’d be willing to bet that she’d do a lot more than 8 mph.
O’Brian has the Surprise do 16 knots once or twice, and I find that a little unlikely (although perhaps not impossible). 14 or 15 knots seemed like a pretty good guess for top speed - do you think it is an out-of-line number?