First off, sorry about the long explanation... I tried to make it as concise as possible. Anyway, here are some pix:
The explanation: The bungee is used to hold the pole up while sailing. When you tip over, you swing the pole out, and clip the cable to the front beam (you'll have to figure out a way of doing this that works for your boat). The swivelling part is a regular castor (like a shelf wheel), with the pole bolted in where the wheel would normally go. The circular part that goes around the dolphin striker is a piece of tubing that was cut in half and welded (poorly, I might add
) to the castor and the sheet metal. Make sure the inside diameter of the tubing matches the outside diameter of your dolphin striker.
Finally, I'd imagine righting your P19 requires roughly the same amount of force that is needed to right my 5.7 (~1730 foot pounds); but I'd base your calculation off of 1900 foot pounds of torque, just to be safe. The formula for figuring torque is really easy--WEIGHT (in pounds) times POLE LENGTH (in feet) equals TORQUE (in foot pounds). So to find the pole length you'll need for your P19, you simply divide 1900 pounds by your weight. For example, if you weigh 190 lbs, then you will need a pole that's exactly 10 feet. (Note: I've obviously oversimplified the calculations. If you're good with calculus, specifically statics problems, I'd be more than happy to give you the formulas I used, so you can be more precise. Calculating the pole length the way I mentioned above should be sufficiently accurate, since I built in a pretty big margin for error.)
If you have any questions please feel free to ask! And sorry again for the long explanation.