How to Choose the Right Yamaha Outboard Motor Cover Size by Horsepower?

Yamaha sizes outboard covers by exact model and physical cowling dimensions, not by a horsepower chart — so match your engine’s model code and measure before you buy.

A 25-hp four-stroke and a 25-hp two-stroke can wear completely different cowlings, which is why horsepower alone gets people the wrong cover. The engines are real: Yamaha’s lineup runs from 2.5 to 450 horsepower, and within the small end alone the F2.5, F4, F5, F6, F8, F9.9, F15, F20, F25G, F40F, F50L, F60, and F70 each carry their own cowling shape. The fix is a five-minute measurement and a careful read of the model plate — and the payoff is a cover that stays put at highway speed instead of flapping paint off your engine.

Does Horsepower Tell You What Cover To Buy?

Horsepower is only a rough starting point for cover shopping, because Yamaha publishes engine specifications by model, shaft length, and physical configuration — never by a horsepower-to-cover-size chart.

Two engines at the same rating can sit on different platforms. The F250H is a 250-hp, 3,352-cm³ V6, and the F200B shares that same 3,352-cm³ V6 block, but the cowling and installed dimensions still follow the model designation, not the number on the side. On the small end, the F40F is a 40-hp, 747-cm³ three-cylinder and the F25G is a 25-hp, 432-cm³ two-cylinder — different engine classes entirely.

Yamaha also still lists two-stroke models like the 40X, 30H, 25B, 15F, 9.9F, 4C, and 4D. A 25-hp two-stroke and a 25-hp four-stroke can require different covers, so treat horsepower as a filter for the catalog, not the answer.

Yamaha Outboard Cover Sizing: What The Model Code Reveals

The model code on the cowling or identification plate is the single most useful piece of information you can write down, because it encodes the engine family, the version suffix, and the shaft length.

Yamaha’s published specs show why the suffix matters. Shaft length changes the installed height of the engine, and the letters S, L, and X mark genuinely different transom heights:

• F40F — S shaft at 414 mm (16.3 in), L shaft at 536 mm (21.1 in).
• F25G — S at 424 mm (16.7 in), L at 551 or 553 mm (21.7 or 21.85 in), X at 640 mm (25.2 in).
• F70 — L at 534 mm (21.0 in), X at 648 mm (25.5 in).
• F100F, F90C, F80D — the 1,832-cm³ inline-four platform, L at 516 mm (20.3 in) and X at 643 mm (25.3 in), depending on model.

Read the full designation — F25G, F40F, F70, F250H — and record horsepower, suffix, and shaft letter together. Skipping the suffix is one of the most common reasons a cover arrives and doesn’t fit.

How Do You Measure And Match A Cover Correctly?

Measure the engine’s covered portion — maximum cowling length, width, and height — then match those numbers against the cover maker’s fitment table rather than the horsepower row.

1. Write down the exact model designation from the cowling plate or owner’s documentation, including the shaft letter.
2. Confirm whether the engine is a Yamaha four-stroke or two-stroke.
3. Measure the covered portion at its widest and tallest points, excluding removable accessories unless the cover will enclose them.
4. Check the shaft length separately, since S, L, and X versions are not interchangeable identifiers for cover dimensions.
5. Match each measurement against the manufacturer’s fitment table, or have a dealer confirm.
6. Decide whether you need a cowling/storage cover, a full outboard cover, or a boat mooring cover — these are different products with different sizing criteria.

Yamaha’s official US accessories page does list covers, but the indexed listing shows a “19 FT | Tower Mooring Cover” starting at $901.99 — a boat cover, not an outboard cowling cover, so don’t read that figure as an engine-cover price. Availability, warranty, and fitment in the US should be confirmed through Yamaha Motor Corporation, U.S.A. or an authorized dealer, since the model specs above come from Yamaha’s global pages. For tested picks that take the guesswork out of the final step, this roundup of the best Yamaha outboard motor covers is a practical place to compare fit options. Yamaha’s own official US covers page is the authoritative reference for what Yamaha sells directly.

What Mistakes Should You Avoid Before Buying?

Most bad fits trace back to four habits: buying by horsepower, ignoring shaft letters, covering a hot or wet engine, and assuming a boat cover is an engine cover.

A loose universal cover can flap at speed, abrade the cowling paint, or detach on the highway. Storage covers may not be rated for highway wind loads, so verify whether the product is built for trailering, storage, or both. Let the engine cool and dry before installing any cover, and avoid trapping moisture or blocking ventilation during long-term storage. After installation, check that the cover is secure, doesn’t obstruct steering or controls, and can’t contact hot exhaust parts or moving components.

One more practical note: a universal-fit cover that looks fine in the driveway can behave very differently at 60 mph. If the maker doesn’t publish a fitment table for your exact model, a dealer confirmation is worth the phone call.