Tackling the 4-Stroke Outboard engine
when No Other Company Would
Outboard engines are power units that integrate an engine, fuel tank, and drive unit to drive a propeller, turning a row boat into a powered boat simply by attaching the engine to the rear of the vessel. Outboard engines are widely used for professional and hobby fishing, and other recreational purposes. Engines range from 2 - to more than 400 - horsepower, with the product’s model number generally indicating the horsepower.
GB30, Honda’s first outboard engine powered by G30 general-purpose engine.
Outboard engines are designed to discharge exhaust gases from the center of the propeller in order to reduce noise. The two-stroke engine, which has long been the mainstay of outboard engines, mixes lubricating oil with fuel for combustion, which causes unburned gases containing oil to be discharged into the water. Honda did not approve of this.
In 1964, Honda launched its first outboard engine, the GB30, powered by a 4-stroke engine. Starting with the T-Type engine launched in 1954, Honda had independently evolved the 4-stroke general-purpose engine that could be used to power a variety of machines. The engine can be removed and used for other tasks. The GB30 was widely acclaimed for its advantages over 2-stroke engines, such as low speed torque, quiet operation, and low fuel consumption, unique to 4-stroke engines.
Entering the Mainstream Mid-size Outboard engine Market
Even after the launch of the GB30, Honda continued to expand its lineup as the only manufacturer of 4-stroke outboard engines, developing a number of unique mechanisms based on its general-purpose engines.
Once Honda’s portable and small outboard engine lineup was almost complete, it began development of mid-size outboard engines aiming to make a full-scale entry into the marine business. Its first models were the BF35A and BF45A. This entry was into the main horsepower class, used for a wide range of applications from fishing to leisure in North America, Europe, Japan, and other markets around the world, and was in response to strong market demand.
The product concept was to be quiet, comfortable, and clean, with the same power performance as a 2-stroke, but with significantly lower fuel consumption. Another goal was to increase the market presence of Honda 4-stroke outboard engines with design and color that further emphasized their uniqueness.
Design and Color Unmistakably a Honda
At the time, the mainstream design of outboard engines was angular. Although the initial design of the BF35A and BF45A was in line with the previous BF series, Honda decided to take on the challenge of a “new design, unmistakably a Honda 4-stroke” amid an environmentally-conscious market questioning the 2-stroke. The project’s designer departed the design studio to spend all day at a marina in the U.S. to look at boats and search for hints.
As he watched the ocean for days on end, he began to form an image that would express a sense of unity between people, nature, and technology. The sketch based on this image depicted a streamlined outboard engine that resembled a dolphin. This was the moment when a completely novel design was born, different to the squarish box-shaped outboard engines that had been the norm. Something, however, was still missing.
Early design sketches
After traveling from marina to marina all over the U.S., he sorted through the photos he took after returning to Japan. One caught his eye: the reflection of the setting sun on the Monterey Bay on the body of a silver Accord he had rented. He was convinced that this was it, because the silver body color looked like gold in the setting sun. Silver is a color that shines beautifully in the ocean, taking in all the colors of nature, such as the orange of the setting sun and the blue of the ocean.
The dolphin-like curves of the outboard blending with the ship, and the silver color that would stand out against the natural surroundings, were the key factors in the new design. To select the best silver color, he then took metal plates coated with variations of silver color, and held them against the oceans of the world to see the subtle differences in the appearance for himself, while also conducting tests by floating the prototype in American waters. The silver outboard reflected the sky in the upper part, making it appear blue, while the lower part reflected the spray of water, making it appear white. There are many things that could only be understood by actually going out to sea. This was Honda’s “Three Reality principle” of place, product and reality, in action.
To Make the World’s Best Mid-size Outboard engine
The BF35A and BF45A were highly acclaimed since their launch in Europe, the United States, and New Zealand in 1990, and received the IMTEC Innovation Award*1 for the most innovative technology at the Chicago Boat Show that year. However, development took five years, of which four years was spent in maturing the specifications. This was the result of a thorough trial-and-error process for each issue, including product planning as well as technical issues. It is no exaggeration to say that the development of the BF35A and BF45A established the concept of Honda’s outboard engines, and the accumulated know-how made it possible to complete subsequent development in a short time.
Through this process, a high-performance outboard engine series was completed that offered superior fuel economy, low environmental impact, and quiet operation compared to 2-stroke engines, as well as durability and operability. The streamlined integrated design, which expresses this performance and matches sporty pleasure boats, stood out from the many square-shaped outboard engines in the market and was instantly recognizable as a Honda at any marina in the world. The BF75 / BF90, and BF115 / BF130 were developed and launched as larger models based on the engines of the BF35A and BF45A. These engines had already won the IMTEC award and the Good Design Award twice, solidifying the identity of the Honda outboard engine series. They also influenced subsequent outboard engines from other manufacturers and set the design trend for clean outboard engines.
- :The most prestigious award in the global marine industry, selected by IMTEC (International Marine Trades & Convention), the world’s largest marine trade show.
BF35A / BF45A established design that was unmistakably Honda.
World’s First to Comply with Lake Constance Navigation
Ordinance
Lake Constance, which straddles the border between Switzerland, Austria, and Germany, is not only a popular tourist destination but also a source of drinking water for the residents living downstream. Since the 1960s, the lake had been polluted by the inflow of sewage (domestic and industrial wastewater), and the three countries, in response to the perceived crisis, established a transboundary conservation committee and began activities to improve the lake’s water quality.
In addition to thorough sewage treatment in the upper reaches of the lake, emission regulations were imposed on the engines of ships navigating on the lake beginning in 1993. The Lake Constance Navigation Ordinance set limits for carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Although a plan to gradually tighten the regulations was considered, strict regulations were set from the beginning due to the drinking water issue.
At the time, the outboard engine market was dominated by 2-stroke engines, which, while emitting less NOx than 4-stroke engines, emitted an order of magnitude greater amount of HC, making it extremely difficult to meet these standards. In contrast, 4-stroke engines have more stable combustion and emit slightly more NOx than 2-stroke engines, but very little HC. After several weeks of repeated setting tests, Honda engineers found the optimal carburetor setting and ignition timing values that would allow the engine to meet the regulation while maintaining easy-to-manage output characteristics. In 1992, the BF8B, launched in four Nordic countries, became the world’s first compliant model, followed by the BF6B and BF40B the next year.
BF8B, the world’s first outboard engine to comply with the Lake Constance Navigation Ordinance
Later, in 1998, the U.S. Environmental Protection Agency (EPA) implemented the U.S. Federal Air Quality Standards for Vessels (a program to gradually reduce emissions with 2006 as its final year), and all Honda models were launched with the ability to easily meet the final year’s regulations from the 1998 model year, and were sold not only in Europe but also in the U.S. and worldwide. Honda’s 4-stroke engines had successfully promoted the image of “Honda 4-stroke clean outboard engines” not only in Europe but also in the U.S. and all over the world. Honda had consistently manufactured 4-stroke outboard engines that do not pollute the water. With the rise of environmental awareness, the times have finally caught up with Honda.
Pursuing Higher Output 4-Stroke Engines
As environmental issues on lakes and oceans became a worldwide concern, market awareness of the Honda outboard engine series as “clean, high-quality 4-stroke engines” grew, while market demand for high-power 4-stroke outboard engines also increased. In the large U.S. market in particular, demand for outboard engines with excellent maintainability expanded, replacing the inboard engines that had been the mainstream for medium and large boats. Honda urgently needed to develop high-output outboard engines.
After a comprehensive market analysis, usage surveys, and requests from the sales division, Honda decided to target 90- and 75-horsepower models. Development was started based on the popular BF35A and BF45A and the know-how accumulated over many years. The challenge was how to develop a highly reliable outboard engine in a short time while minimizing development costs, given the small number of units compared to smaller models.
Although higher output requires a larger displacement, Honda had the advantage of its automobile business. In 1995, the BF90 / BF75, the first 4-stroke outboard engines in this class, were born.
The BF90 and BF75 further increased awareness of the 4-stroke engines’ appeal, and sales of the small to mid-size series also grew rapidly.
The BF90 and BF75 were developed to meet market needs for high output 4-stroke outboard engines, and became the first 4-stroke models in their class.
Realizing Higher Output and Lower Environmental Impact
By Applying More Automobile Technologies
Soon after the release of the BF90 and BF75, the development of an even higher output model began. The goal was to raise the output of the 4-stroke outboard engines, which had previously been 90 hp, up to 130 hp, while at the same time achieving an extremely low environmental impact. The development of the BF130 and BF115, which followed, was an aggressive “marinization of automobile technology,” in which many of the technologies that had been established for performance and reliability in automobiles were converted to marine use.
The engine was based on the Accord’s 2,254 cc SOHC inline 4-cylinder 16-valve engine. The lubrication mechanism was modified, as unlike automobiles, outboard engines are mounted with the crankshaft upright. The water-cooling system was also completely different because it uses seawater for cooling. Through this “marinization” process, the engine was optimized as an outboard engine.
The BF130 / BF115’s biggest technical hurdle was developing the first electronically controlled fuel injection system (PGM-FI) for large 4-stroke outboard engines. The new system was developed by making full use of the mature automobile electronic fuel injection (EFI) technology which was further modified from various angles, including a marinized control system. This not only achieved a high level of compatibility between reduced emissions and improved performance, such as ease-of-starting and low-speed stability, which had been limited with carbureted outboard engines, but also laid the technological foundation that could be applied to increasingly complex and diverse customer and societal needs in the future.
The BF130 and BF115 were launched in 1998. In addition to high output, the engines’ environmental impact was well below the 2006 values, the final year of the EPA's exhaust gas emission regulations for marine engines. In addition, high reliability and reduced manufacturing costs were achieved by diverting automobile engine parts for the engine and by using frame parts from the BF90.
BF130 / BF115 was powered by Accord-based engines, and became the first large 4-stroke outboard engines with automobile PGM-FI technology.
Higher Performance, Lower Fuel Consumption
As the pioneer of 4-stroke outboard engines, Honda has always pursued “the creation and realization of industry-leading engine technology” and in 2001 launched the BF225, the BF series flagship model, which met California Air Resources Board’s (CARB) 2008 emission standards. The BF225 was developed based on a 3.5L V6 engine with VTEC and PGM-FI, which had powered the Lagreat and other models.
VTEC is a variable valve timing lift mechanism that increases intake efficiency by switching the amount and timing of valve opening and closing when the engine speed increases. Through tight integration with PGM-FI, the BF225 achieved, for the first time in its class, environmental performance compliant to CARB’s 2008 emission standards, the most stringent in the world at that time, while delivering almost the same dynamic performance as a direct-injection 2-stroke outboard engine.
BF225 with V6 VTEC engine
Many vessels in this power range are equipped with two, not one, outboard engines. In general, the two outboard engines are positioned as close as possible to the center of the boat’s rear end to prevent the propellers from lifting out of the water when turning. 4-stroke outboard engines have a larger displacement than 2-stroke engines to ensure power output, as well as valve and cam shafts among other valve train components which tends to increase the width, especially for V-configuration engines. Most existing boats had engine mounts designed to accommodate two 2-stroke outboard engines, so if wider outboard engines were installed, they would interfere with each other. Honda’s V-Wing form, which narrows the width of the front of the engine cover, achieved a separation between the two engine mounts of 660 mm, the industry standard, allowing two 4-stroke engines to be mounted in place of 2-stroke engines, a world’s first for 200 hp class 4-stroke outboard engines.
In 2006, the BF90 and BF75 were fully revamped. Based on the Fit’s 1.5L engine, the BF90 and BF75 became the first outboard engines in the world to adopt the BLAST intelligent technology, which improves acceleration on startup by amplifying torque through optimal control of fuel supply and ignition timing, including VTEC*2, PGM-FI, and lean burn control. In addition to a 20%*3 improvement in fuel economy, BLAST also improved maximum speed and acceleration compared to the previous generation BF90 and BF75 models. The new model received high acclaim for its low noise and vibration, light and compact body, and excellent dynamic performance, breaking through conventional outboard engine concepts.
In 2011, Honda launched the BF250, based on the BF225, combining a newly developed 3.6L V6 VTEC engine and a direct air intake system, the world's first*4 technology for an outboard engine.
- BF90
- Compared to previous model BF90, based on fuel consumption rate in EPA EM measurement mode, according to Honda research.
- Honda research as of October 2011
BF250 equipped with the world’s first direct air intake system for an outboard engine
Aiming for Carbon Neutrality for the Ocean
The market share of 4-stroke outboard engines, which was less than 1% when Honda first entered the market, is now 98%. Honda has laid the foundation for the shift to 4-stroke outboard engines and has led the way in improving the marine environment, supplying to 59 countries including Japan products tailored to their needs as of 2021, Honda’s cumulative global production reached 200,000 units. Clean, fuel-efficient, and quiet 4-stroke outboard engines are playing a large role in the world’s oceans, rivers, and lakes.
In 2021, Honda introduced the concept model of a compact electric propulsion system as the next-generation clean outboard engine, aiming to achieve the goal of carbon neutrality through all Honda products and corporate activities by 2050. In addition to being zero-emission, its features such as low noise, low vibration, and high torque from take-off have the potential to further expand the use of outboard engines. In addition to these and other initiatives, Honda is working to achieve carbon neutrality in marine mobility.
Honda is committed to its beliefs, and will do what other manufacturers will not. Inheriting its founding DNA of “creating things that don’t exist,” Honda will continue to produce outboard engines that exceed customers' expectations.
