The Casting that Turned Boating Upside Down

Kim Phelan

The announcement was out: Recreational products manufacturer BRP was discontinuing its iconic Evinrude line of outboard engines. For employees at the Sturtevant, Wisconsin, plant that built them, the landscape was changing. A hint in the company’s official press release on May 27, 2020, lifted the curtain hem on something brewing that might just take the boating industry by storm. Way at the bottom of the statement was a curious reference to a next generation marine engine technology called “Project Ghost,” an internal code name for a new product they believed would transform recreational boating.

Until then, boat manufacturers and their customers had two options: an outboard engine that sits prominently (and even obtrusively) at the rear of the boat close to where passengers sit, or a stern drive/inboard engine that’s housed somewhere inside the boat, taking up precious, though unseen, cargo space. BRP conceptualized a third, unheard of alternative they called stealth technology––an outboard engine that is fully and unobtrusively integrated with the boat, virtually out of sight and out of mind. 

To achieve such a feat would, in part, require a complex front housing casting to hold the lower unit and gearbox assembly that enables a 150 hp engine to reside sleekly below the boat. The BRP team––comprising Supplier Quality Development Engineer Dave Palmer, also an instructor of AFS technical programs; Product Designer Roger Raetzman; and Senior Buyer Jim Milam––eventually selected AFS Corporate Member LeSueur Inc. (LSI), LeSueur, Minnesota, to produce the 76-lb. aluminum (A356) casting that measures 28.33 in. long x 21.98 in. wide x 23.80 in. high. 

“I’m very pleased that we were able to easily integrate this casting into production,” Palmer reflected. “This is a challenging casting. And it’s a big casting. It needs to be dimensionally accurate, have effective structural properties and be cosmetically appealing.  This housing is a testament to the great collaboration that we’ve had with LSI.”

Known commercially as Rotax S, the outboard engine is currently available on BRP’s Manitou pontoon boats, its Alumacraft fishing boats, as well as its Australia brand of Quintrex boats. 

Brains Plus Beauty

Fitting the Rotax S outboard engine underneath a boat’s swim platform would mean BRP engineers would have to take a traditional outboard engine and essentially turn it on its side. To do so, they replaced a typical vertical crankshaft with a horizontal crankshaft, which reduced the engine’s overall height. The output of the horizontal crankshaft would then be channeled through a gearbox down to the outboard’s lower unit.

“When you stand next to some of the big new outboards today, you feel like you’re about three feet tall because the engine is just so tall,” said Palmer. “Putting the crankshaft in a horizontal orientation allows us to keep within that profile to be able to fit the engine under the deck. This means, we have to have an additional gearbox, made at BRP’s lost foam foundry in Spruce Pine, North Carolina, to take the output of that crankshaft down to the propeller shaft.” 
“The front housing that LeSueur makes is what holds all of this together, so it’s really an important casting,” Palmer continued. “That’s really what’s allowing us to make an outboard engine like this with a horizontal crankshaft, and it’s a brand-new part for us––I mean, this is something completely revolutionary.”
Besides the innovative engineering to reconfigure engine parts for a slimmer, “stealth” fit below deck, the casting required excellent cosmetic features, which low pressure permanent mold was better equipped to handle than lost foam, which had been considered.  But why does an under-the-boat engine need to look good?

“It’s not necessarily visible when you’re on the boat, but it is when you’re in the showroom,” said Palmer. “And that’s equally if not more important, because if the customer doesn’t like the way it looks in the showroom, they’re not likely to buy the boat or see it in the water.” 

Knowing the casting must retain its corrosion resistance and beauty for many years, the casting’s coating supply chain is elaborate. Once delivered, BRP machines the parts and applies chromate conversion coating. From there, an e-coat is applied and it is painted before it is ready for final assembly.

Start Your Engines

Co-development for the front housing was a guiding principle from the start. In fact, the back-and-forth design discussions were underway even before the project went out for bid.

“BRP originally sent us a very complex part. It was decided to split up this complexity and keep the front housing as a separate casting,” said LSI Director of Engineering and Quality Carlos Esparza. “Other internal features for this part would be done at the BRP lost foam foundry.”

It was then that LSI decided to rise to the occasion. While the RFQ for the Rotax casting was still circulating among select casting suppliers, the foundry assertively jumped into preliminary simulation design work, making more recommendations for manufacturability well before they were awarded the project, demonstrating their commitment and enthusiasm to win the job. 

“We encountered many challenges that we were able to solve, and we were committed to helping BRP reach a new height in technology,” Esparza said.  “All the LSI engineers involved in the development of this project were excited and eager to participate, knowing that they were helping to create a new advanced casting, pushing the boundaries of the existing aluminum foundry standards.”
LeSueur’s use of simulation technology was a major value-add to the process, according to Raetzman.

“Their in-house CAD modeling capabilities were really helpful because it decreased the development time,” he said. “If I was required, as a customer, to make every design iteration, every conceptual modification to the model, that would have added a lot to the timeline. Many times, early on and throughout the cycle, they would actually just go through many loops internally. And once they got to a point where they were comfortable with it, they would give me a rough model and say, ‘Hey, we had good results during the simulation; how about we add something like this to the DMU [digital mock-up]?’ They were thinking at a higher, broad-brush level about what kind of geometry does this part want, and from there we could look at a more refined part.”

The Need for Feed

Geometry was one of the stickier design issues the group encountered, and eventually, one of the original plans for high pressure diecasting was also ruled out in favor of low pressure permanent mold casting, Milam recalled. 

“LeSueur worked very aggressively with us to change the geometry that needed to be changed, to identify areas that were going to be an issue and then make adjustments,” he said. “Sometimes we were doing multiple simulations, two or three a week, trying to get to the final design that would be castable and meet our requirements.”

Raetzman added, “We have areas that required heavy bolt bosses, mounting flanges, and sealing grooves but they were kind of opposite of where the gate needed to be based upon the molding of the part,” Raetzman said. “So, there were numerous simulation loops where we were trying to thicken walls and add ribs to act as kind of internal feeder features to feed these heavy sections that we really needed. 

“Fortunately, we got the development process started early so that we could adjust the design as needed,” he added. “We tried to be as flexible as possible with LeSueur, because we both wanted a good part. At times, we were adding significant amounts of material, and I would have never thought to make this wall 15mm thick, for example. But that’s what was needed to feed the extremities of this large part.”

The large size pushed the limits of LeSueur’s low pressure machine and some modifications were needed to it in order to accept the tooling, Esparza said. Another challenge was its complexity, even after the design was simplified to only function as a front housing. 

“The casting is very tall on one side, and the other side is very short––in other words, you need more metal on one side, which makes it quite complex,” he said. “We started with trying to use only one feeder in the big mass area, but at the end we knew that we needed more feeding, maybe two, three, four gates to feed the casting all at the same time.”

Nothing turns up the heat in a foundry like late-game design changes, but with a first-of-its-kind product, alterations were almost inevitable. One example was the BRP team’s discovery of a complication related to how splashing water affected the front housing’s hydrodynamic—at first, they considered adding sheet metal deflectors, but a better idea was to incorporate fin-like features into the casting itself. And LeSueur gladly obliged. 

The success of the Rotax S project was no mystery, sources at both companies agreed. Open, honest communication and collaboration throughout the development was essential, and it’s still ongoing. 

Milam said, “Now that we’re in production, LSI continues to bring good ideas to the table. LSI Senior Project Engineer Luis Beltran is unparalleled with anybody I’ve worked with as far as trying to improve the part.”

Palmer added, “Any issues that we bring to their attention, they respond very quickly. They come up with good corrective actions that solve the issues. And if there are changes they need that will allow them to make a better casting, they haven’t hesitated to bring those to our attention, either. The continuous improvement has really been good––and it’s been ongoing ever since the launch of this part.”