With our 20" prop maxed out at 2500 rpm Gerr's equation indicates about 1000 lbs of pull

1000 rpm generates about 500 pounds, or equal to about 35 knots wind.

All that sounds good, but we set at 2000 rpm (calculates = about 45 knots wind) a few days ago then dragged in 30 knots when an huge wash hit us. Bottom was mud/sand, and we had a fishing net on the hook when we got it up.

1000 lbs is equal to about 50 knots wind according to Dashew.
When I get home in the winter I will look at Oceanography and Seamanship which has some good data on anchor loads

Anybody have data on wind and wave loads on anchored yachts? (We are a 47 ft sloop with a bit less than average cabin height to create windage, but we sail around fairly badly at anchor)