I would think in a heavy blow that the snatch block would be fairly stable and only ride forward or aft with a significant change in the pressure applied to the parachute. I did not that he found a huge difference in the volume of water with only a relatively small change in parachute size. For example, in the book he talked about the volume doubling when increasing diameter from 8 to 12-feet. Also he talked of the effectiveness with different lengths of the anchor rode and said it was imperative to get the parachute out to at least the second trough. I read another book where the author added a 10-foot length of chain, which placed the parachute about 20 feet below the surface, which decreased the amount of turbulence on the chute. As Pardey point out, this is NOT an exact science, the you'll have to experiment a bit to get the right combination and best results. He also pointed out that during a 70-MPH blow that lasted 3 days he was accompanied by a couple large, container ships that also hove to during the storm and incurred no significant damage. One of the larger sailboats, a 76-footer, tried to outrun the storm and attempted to take refuge behind a reef. The boat suffered a 90-degree knockdown, several crew members were injured and the boat was nearly destroyed. Like I said previously, I'm going to do my best to avoid these conditions.