Why are outboard engines rated at 9.9 horsepower instead of 10?

Outboard engines are a critical component of any watercraft, providing necessary thrust for powering boats and other vessels on the water. These engines are typically rated in horsepower, reflecting their maximum output and allowing boaters to choose an engine that matches their needs and vessel size.

One surprising fact about outboard engines, however, is that many are rated at 9.9 horsepower instead of an even 10.00. This unusual number may seem arbitrary, but there are actually some good reasons why 9.9 horsepower is a common power rating for these engines.

One major reason for the 9.9 horsepower rating is related to boating regulations and safety standards. Many countries, including the United States, have laws and guidelines that distinguish between different types of boats based on their power output. In the US, for example, boats with an engine rated at 10 horsepower or more are required to follow certain safety rules, such as carrying lifejackets, displaying a registration number, and using proper navigation lights.

By rating their engines at 9.9 horsepower, manufacturers can create engines that are slightly below this regulatory threshold, making them more accessible to boaters who don’t want to deal with the added hassle and paperwork of owning a more powerful boat. This means that boaters can enjoy many of the benefits of a larger engine, such as better speed and handling, without having to deal with the extra regulatory burdens.

Another reason why 9.9 horsepower is a common rating for outboard engines is related to their design and performance characteristics. Many smaller boats, such as dinghies, kayaks, and canoes, are not designed to handle extremely powerful engines. In fact, a motor rated at 10 horsepower or more could easily overwhelm these lightweight vessels and make them unstable on the water.

By rating their engines at 9.9 horsepower, manufacturers can create engines that are ideal for use on these smaller boats, providing the necessary power and thrust without causing any safety concerns or performance issues. This allows boaters to choose an outboard engine that is specifically designed for their vessel and boating style, ensuring a safe and enjoyable experience on the water.

The rating of outboard engines at 9.9 horsepower instead of 10 may seem strange at first, but it is actually a smart design decision that takes into account both regulatory requirements and vessel performance characteristics. By choosing an outboard engine with a 9.9 horsepower rating, boaters can enjoy a powerful and efficient motor that is perfectly suited to their boating needs.

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