10 vs. 9.9 HP Outboards: What’s the Difference? [Video]

Major brands mainly market 9.9 HP outboards instead of 10 HP because of legal considerations. In the past, many states in the US didn’t require a registration on boats with engines with less than 10 HP. Although today every motorboat has to be registered in the US, manufacturers are sticking to their 9.9 HP models. This is no surprise since many inland bodies of water still have an “under 10 HP” restriction for motorboats.

On top of that, in many other countries boats under 10 HP can still be operated without a registration and/or a boating license.

If you want to find out more about 9.9 HP outboards, this post is for you.

We at PowerSportsGuide have compiled all you need to know about these motors under one roof!

Why Are Many Outboards Rated at 9.9 HP?

There are many reasons why manufacturers offer outboards with an engine power of 9.9 HP instead of 10 HP, but the most important ones are as follows:

  • Many years ago, motorboats with less than 10 HP didn’t have to be registered in the US. (This federal law has been changed over the years.)
  • Certain inland water bodies in the US still have an “under 10 HP” restriction for motorboats.
  • Many states require you to obtain a Boating Safety Education Identification Card to legally operate a boat of 10 HP or greater. This means boats with 9.9 or less HP can be operated without a license in certain states (however, it often depends on the age of the operator as well).
  • In many other countries boats powered with less than 10 HP don’t have to be registered or can be operated without a license.

Due to these legal regulations, the major manufacturers offer their “10 HP” outboards with 9.9 HP.

How Much HP does a 9.9 Outboard Have?

As the name suggests, 9.9 outboards are powered by 9.9 HP power heads.

These engines are typically 4-stroke, 208-362cc, carbureted, inline-2 power sources.

You can expect the weight of these motors to be in the ballpark of 80-130 pounds.

They are often marketed with both electric and manual starting systems, as well as mechanical or tiller steering.

The available features and accessories vary depending on the make and model.

What is the Difference Between 8 HP and 9.9 HP Outboard?

8 and 9.9 HP outboard motors of the same brand often feature the same power head and gearbox.

The main difference between them is that 8 HP models come with a restricted engine detuned for 8 HP.

Besides this power cut, 8 HP models often come with simpler features. For example, certain manufacturers only offer 8 HP motors with tiller steering or a manual start.

Other manufacturers (like Suzuki and Tohatsu) market their 9.9 HP outboards as the smallest brothers of the 9.9/15/20 HP series.

This means these 9.9, 15, and 20 HP outboards feature the same anatomy.

As one may expect, many of these 9.9 HP models run in an “upgraded” condition, meaning that the owners remove the restriction from the engine to increase the power.

Despite its popularity, this practice is obviously not legal!


Major outboard manufacturers offer 9.9 HP motors instead of 10 HP due to legal considerations.

Certain inland bodies of water still have restrictions for powerboats; many of them only allow boats with an engine power of less than 10 HP.

Also, in certain states boats with 9.9 or less HP can be operated without a boating license.

When it comes to other countries, many of them allow boaters to operate a motorboat with 9.9 HP or less without a license and/or registration.

Because of these various restrictions, manufacturers offer their outboards with 9.9 HP instead of 10 HP.


epropulsion.com, boat-ed.com

Recent Content