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Electric Boat Costs 40–50€ to Cross Baltic Sea, vs 750€ Refueling Gas Boat
(cleantechnica.com)
This is a most excellent place for technology news and articles.
Exactly. Hydrofoils have a bunch of downsides (more expensive to buy and maintain, don't work in shallow water, don't work with big waves, etc), so it's not like the average boat owner can simply switch to a hydrofoil boat. It's a cool solution if it works in your particular area, but they're not a drop-in replacement.