The Styrofoam is there for floatation. Back in the day, there was no "encapsulated" foam. Lot's of older built dingy's had plain Styrofoam inside for floatation. I also seem to recall some sailing dingy's built entirely of Styrofoam, name escapes me at the moment.
From Wikipedia:
The
Snark is a lightweight, two-person,
lateen-rigged sailboat manufactured and marketed by Meyers Boat Company of
Adrian, Michigan. The Snark was initially marketed by Snark Products, Inc. of
Fort Lee, New Jersey and has been marketed with numerous slight variations, most prominently as the Sea Snark, Super Snark and Super Sea Snark.
The sailboat was marketed heavily in numerous
co-branding campaigns.
The New York Times reported that the Sea Snark outsold all other sailboats in 1970
[1] and that over 48,000 Sea Snarks were sold in an 18-month period in 1971 via a
mail order campaign with Kool Cigarettes.
[2] By 1973, over 200,000 Sea Snarks had been sold
[3] and
The New York Times reported that by 1976 that Snark had built more sailboats than any other manufacturer.
[4] The manufacturer currently estimates that nearly a half million
[5] Sea Snarks have been manufactured since 1958.
[6]
Noted for its 11'
expanded polystyrene hull and marketed as "unsinkable", a 1971
Popular Science reviewer doubted there was a sailboat "more foolproof".
[7] Originally, the purchase of a Sea Snark included a 16 page booklet on "how to sail",
[8] and a 1975
Popular Science article described the Sea Snark as the least expensive and lightest sailboat on the market.
[9]
Early Sea Snarks featured an unclad one-piece injection-molded
EPS hull and weighed a total of approximately 30 lbs.
More here:
Snark sailboat - Wikipedia