The hornets nest link doesn't say, but that looks like a fairly light boat. ST tires generally carry more load. I had a 14"D blow out, went to WalMart, car tires were too light. I now use 15" D tires, carry over 2500#'s ea. What kind of car tires would work here? In larger, heavier sizes, truck tires get really pricey.
"Not for use on passenger cars"? ST tires are not designed for steering or accleration traction as car tires. Narrower? Yes, narrower tires give better economy (see above).
The extra psi per Goodyear bulletin will provide a cooler running tire. After running 1-95 in Florida @ 75mph in July, I want the coolest set-up I can get!