I was reading through
Earth is Not a Globe and decided to conduct one of the experiments as suggested by this site and the author.
While reading through Section 2 of the version that I found on Google (
http://books.google.com/books?id=oTUDAAAAQAAJ&printsec=frontcover&dq=Earth+Not+a+GlobeI saw the experiment about dropping objects off of the mast and decided that it would be a perfect first experiment.

The derrick on the rig is 50 meters from the top to the rig floor.

While underway avoiding Gustav was the perfect time to conduct the experiment. So I made sure that there was no one on the rig floor, and then tossed a shackle straight into the air.

It rose and then fell straight down to the rig floor. I repeated the experiment with a wrench. Still a straight drop.
Well, maybe 4 knots wasn't fast enough. I tried the experiment again while on the crewboat to the beach. This time I was tossing peanuts up about 10 feet and then watching to see where they fell. I tossed the peanut up and it landed at my feet.
Well, maybe 20 knots wasn't fast enough. Not having a train handy...

I decided to repeat the experiment on an airplane in flight. This time I was unable to toss the peanut 10 feet, so I was tossing it the three feet to the overhead. The peanut still came straight down into my lap.
Based on these experiments, I can concluded that dropping balls off of the mast of sailing vessels does nothing to prove whether there is motion present. So Rowbotham's conclusion...

is flawed.