Stone-Skipping Efficiency

Finding flat stones and skipping them across the water is a great activity for kids of all ages. I have some really nice memories of skipping stones with my dad, with my children, with my nephew, and with my grandchildren.

What do you think is the most efficient angle for the stone to hit the water (if you're trying to make the stones skip a lot of times)?[Quotation below and link via CBC, courtesy of cmt]

Throwers should tilt stones about 20 degrees to the lake's surface, an angle first predicted by French researchers last year.

Shin-ichiro Nagahiro and Yoshinori Hayakawa of the Tohoku University Department of Physics in Sendai, Japan, created a mathematical formula to confirm the French experiment.

The Japanese researchers used a numerical method called smoothed particle hydrodynamics to simulate the skipping stone.

They also derived an equation describing the disk's motion.
Both methods provided a confirmation of the magic angle of about 20 degrees.

What do you think the record is for the most skips for one throw of a stone?

38, according Nature magazine, also quoted by the CBC. I guess they must have used a slo-mo replay to count them.

I wonder what the optimal weight of the stone is, and whether the optimal weight varies from fresh water to salt water.