Boat engine maker Evinrude provides the following reasons why boat engines have more problems with ethanol gas:

Boaters often store gas in tanks longer than recommended for E10 (90 days). Cars, unlike boats, usually replace fuel every week or two, which successfully prevents the possibility of water-contamination or phase separation, a common problem with ethanol-blended fuels.

Boat engines live in a water environment — alcohol gas (ethanol) loves to absorb water. Ethanol E10 gas can absorb large amounts of water into the fuel tank that conventionally treated gasoline does not.

Boat engines usually last longer than cars. Evinrude points out that many boat owners still own and use marine engines from the 1970s or 1980s. These older engine parts and tanks usually were not designed or tested to withstand the damaging effects of ethanol-treated gas.

Some older marine engines (made prior to 1992) have plastic and rubber parts and fiberglass tanks that are not compatible with E10 alcohol fuel.