[sailingdog]

A couple of points that seem to be missed so far. While both a JSD and a Sea anchor tend to keep the boat from moving with any real speed, the JSD loads up proportionally, and has some give to it initially, depending on the loads and the speed the boat is moving at—a parachute sea anchor does not. When a breaking wave hits a boat tethered to a JSD, the JSD loads up progressively, slowing the boat more as more of the JSD comes under tension. This progressive loading allows the boat to rise with the wave and allows the JSD to pull the boat through the crest of the wave. A parachute sea anchor does not load progressively—it is either loaded or the rode is slack. If the rode is slack, there is a risk of the parachute collapsing or not re-filling properly. If the rode is loaded, then there is very little, if any, give to the connection, and the boat isn't allowed to rise with the wave, but is forced to get hit with the full force of it—rather than moving through it.

Also, most modern boats have far more buoyancy in the stern than they do forward, since the bows are normally fairly fine entry and on modern designs the beam is usually led pretty far aft. The stern will have a greater tendency to rise with the wave due to the greater buoyancy.

These two things, combined with the greater dynamic stability of a drogue deployed from the stern, mean that the JSD creates far lower shock loads and allows the boat to escape much of the damage that can occur when using a parachute sea anchor deployed from the bow.