From furnace to finish

Chris Beattie | VOLUME 30, ISSUE 3
Mercury propellers being cast from the foundry.
A day in the birth of a new Mercury Verado.

Let me confess upfront that I have a fetish for factories. Banks of clanking automated machines, giant hissing robots weaving this way and that, drawers full of intricate components and assembly lines with complex tools and lots of whirring widgets do it for me. So when the world’s biggest manufacturer of marine engines issued an invitation to visit its factory, the RSVP was immediately reassembled, quality checked and then repacked and returned for processing.

In the US in 2015 to also attend Mercury’s launch of its 350 and 400R Verado outboards, I also took the opportunity to visit the company’s huge engine plant in Fond du Lac in the northern state of Wisconsin.

Having celebrated its 75th anniversary in 2014, Mercury is a company rich in maritime history. Founded by energetic engineer and entrepreneur Carl Kiekhaefer in 1939, a man as famous for his tempestuous temperament as for his astute commercial sense, it is today the world’s most recognisable marine brand.

Now owned by the giant Brunswick Corporation, Mercury manufactures a huge range of powerplants to suit virtually all recreational boating applications, from the smallest outboards to the largest racing engines. It also makes sterndrives and manufactures its own propellers.

The 52 hectare Fond du Lac facility is actually a collection of various specialist factories that all feed into the largest building, where finally assembly of the powerplants and gearcases is undertaken. There are three outboard engine assembly lines covering the larger four-strokes, the Optimax two-strokes and the Verados, while another area is set aside for the various four-, six- and eight-cylinder sterndrives. Around 3000 employees work at the plant.


We were hosted at the factory by Robin Senger, Global Product Training Manager, whose enthusiasm for the brand obviously runs deep. In a packed day, we witnessed pretty much the entire Verado manufacturing process, from foundry through to final assembly and testing.

There is a clinical tidiness and order that is the hallmark of all successful manufacturing enterprises, with clearly delineated areas for the various specialised processes that are required to build the largest range of marine powerplants on the planet.

Initially we were shown through the engine testing area, where prototypes are tested up to and beyond breaking point in special modules. The idea is to detect any weaknesses in individual components and systems before they find their way to market. Each prototype engine endures a variety of tests, including being run for 300 hours on wide open throttle – so all models have been exhaustively assessed before they ever find their way onto or into a boat.

Our tour also included the foundry, which has an almost medieval feel to it. In particular, the area where the stainless steel propellers begin life is a study in the timeless process of giving shape to molten metal. Flames and smoke belch from furnaces as workers enveloped in fire-resistant garb almost ritualistically pour flaming molten metal into moulds. In the other section of the foundry where engine and other components are cast, the process is more automated, but nevertheless fascinating as fiery furnaces disgorge their super-heated liquid contents into complex moulds.

Mercury employs a process called ‘lost foam’ for its aluminium castings, which involves using complex and detailed styrofoam moulds that dissolve once the metal is poured. It allows for more intricate shapes and much tighter control of casting quality, with less final machining and finishing required to major engine castings, such as cylinder blocks and heads.

After castings have been removed from the moulds, they are subjected to a high-pressure baking process to relieve stresses and ensure strength.


Mercury has invested a lot of research and development into its special corrosion-resistant engine alloys and also has its own patented anti-corrosion treatments for major castings. The MercFusion procedure involves an irridite metal preparation and sealing process, followed by Mercury’s Electro Deposition Paint priming stage, and finally a powder top coat.

Contrasting sharply with the foundry is the more clinical machining section, where raw castings of engine blocks, cylinder heads, gear casings and the many associated components are carved into shape on rows of computer-controlled mills, lathes and automated welding equipment. There is much automation in this area, with robots feeding castings into machines that produce parts to within the finest manufacturing tolerances, measured in millionths of a metre.

Around 70 per cent of all engine and driveline components are manufactured in-house, with the remainder sourced from outside suppliers.

We also visited the quality-control section, a special area which has an almost laboratory feel to it. Here staff oversee what one employee described as the “ruthless” process of ensuring that all parts constantly adhered to specifications. Components are randomly taken from the manufacturing plants and tested and measured using finely calibrated equipment. The QC staff are particularly hard on outside-sourced componentry to ensure that suppliers don’t allow standards to slip.

Quality control has been a major focus at Fond du Lac in recent years, we were told, with warranty costs plunging by an impressive 90 per cent over the past five years as quality monitoring has tightened up.


In contrast to the machining plants, the Verado assembly line is refreshingly manned by humans, who diligently go about their tasks like anyone who knows exactly what they’re doing. All workstations are well-organised and supplied with exactly the right parts to suit the production cycle, whether it’s for a 135hp, four-cylinder engine or the 350hp six, which is the most recent introduction to the Verado line-up.

At each stage of the process individual workers are responsible for their own work and the whole process has a flow to it as any hold-ups affect the whole line.

As crankcases are filled with crankshafts and pistons, cylinder heads are crammed full of valves and camshafts, each intricate assembly is finally mated using Mercury’s unique long bolt design, which rigidly secures all major engine assemblies to ensure maximum strength and integrity.

Next, the central housings and gearcases are mated to the powerheads and all cowlings are fitted. Total assembly time for a typical Verado from start to finish is 38 to 44 minutes, according to Mercury.

Finally, each engine is run on a special test rig for at least 10 minutes, from idle to wide open throttle. If all readings are within spec, it’s off to the packing department and eventually to the market.

While production occupies most staff, many are involved in research and development and the company continues to develop new ways to power the recreational boating lifestyles of its customers across the globe.