How Zzzap sees tires

“There’s something between them, keeping the boats from hitting each other too hard. Maybe tires?”
A frown crossed Captain Freedom’s face. “Tires?”
Barry shrugged. “A bunch of round, nonconductive, and slightly magnetic objects, two or three degrees warmer than the water.” He tapped his temple by his eyes. “They looked like tires to me.”

Excerpt From Ex-Isle, pg 73
Peter Clines
https://books.apple.com/us/book/ex-isle/id989619017