How Fast Is a 4HP Outboard Motor? | Real Numbers and Limits

A 4 HP outboard motor typically moves a small boat at 14 to 18 mph, depending on hull design, weight, and load.

If you’re sizing a motor for a kayak, inflatable, jon boat, or small skiff, speed matters more than the horsepower number on the box. The honest answer to how fast a 4HP outboard motor goes is “it depends,” but real-world testing gives you a solid ballpark.

That’s the short version. Below, we break down the verified speeds, why they vary so much, and what the current 4 HP models cost so you can compare your options.

What Determines a 4 HP Outboard’s Speed?

Hull shape is the biggest factor. A light, flat-bottomed jon boat or inflatable can plane more easily and run faster than a deep-V hull or heavy fiberglass skiff that’s stuck in displacement mode. Load matters just as much — the same motor that pushes one angler to 17 mph drops several miles per hour with a second person, a cooler, and gear onboard.

Those numbers line up with what boaters typically see: low teens to mid-teens mph on a light load, with occasional bursts higher on ideal hulls.

Propeller pitch, trim angle, water conditions, and even how the motor is mounted on the transom all nudge the final number up or down.

Current 4 HP Outboard Models: Specs and Prices

Retail prices shift by seller and season, but the current U.S. listings show what you’ll pay today. Shaft length matters more than most buyers realize — a 15″ short shaft fits small transoms, while a 20″ long shaft is needed for higher transoms on sailboats and some inflatables. Match the shaft to your boat before you buy, or the motor will cavitate and underperform.

All of these are 4-stroke, single-cylinder motors with manual start and tiller control. The internal fuel tanks hold roughly 0.3 gallons, so expect frequent refills on long days — a portable tank is worth considering if you cover a lot of water.

Is 4 HP Fast Enough for Your Boat?

That depends on what “enough” means to you. For trolling, puttering along rivers, or cruising a small lake, 4 HP delivers a relaxed ride at maybe half throttle. For getting to a fishing spot quickly or running a mile across open water, the low-to-mid teens mph pace will feel unhurried — a 10-minute trip becomes 20.

If you’re chasing speed, this isn’t the class for you. A 6 HP or 9.9 HP motor adds several mph and lets a heavier boat climb onto plane. But the trade-offs are weight and cost — a 4 HP sits comfortably at 55 to 57 lb and can often be carried by one person, which is why it’s the sweet spot for small craft.

The best 4hp outboard motor for small boats depends on your weight budget and transom height, not just top speed.

FAQs

How much fuel does a 4 HP outboard use?

Fuel consumption depends on throttle position, hull, and load. At cruising speeds you’ll use less, but a full internal tank won’t get you through a long day on the water.

Can a 4 HP outboard plane a boat?

Yes, but only under the right conditions. A light jon boat or small inflatable with one person aboard can climb onto plane with 4 HP, as the Mercury test showed at 15 knots with a single passenger. Add weight or choose a deeper hull, and the motor will fall back to pushing the boat through the water rather than over it.

What size boat is 4 HP good for?

A 4 HP outboard suits boats up to roughly 12 to 14 feet — kayaks, inflatables, dinghies, and small jon boats. The motor’s weight stays manageable at around 55 lb, and the thrust is adequate for a light craft. Larger hulls or heavily loaded boats will feel underpowered.