Manufacturing Process

Producing world-class Mercury propellers is no simple task

There's nothing to producing a boat propeller right? Think again. Producing a world-renowned Mercury Marine prop takes time and skill, not to mention advanced engineering and know-how.

Three dozen Mercury employees create some of the best props in the world. Every operation - from inception to completion - is centralized at Mercury's propeller manufacturing facility in Fond du Lac, Wisconsin.

Mercury Marine started producing propellers 16 years ago and today its propellers are revered around the world.

Manufacturing Mercury props starts with a 5,000-year-old process - investment casting - which requires specially engineered wax to create a prop mold.

The wax is warmed to 180 degrees and poured into a "wax press," where a machine operator creates a pattern in the shape of the propeller.

Next, the pattern is dipped into two ceramic finishes. It's initially dipped in a primary coating and left to air dry for two hours. Then it's dipped four more times in a secondary finish that improves thickness and strength. In between each dipping, there is another five-hour drying period. After all five coatings are applied, the pattern is left to dry under high-powered fans for 24 hours. The entire dipping process takes more than two days.

Once there's a strong, thick ceramic shell, the wax pattern can be removed. Each piece is placed in an autoclave where the molds are steam-heated for 18 minutes at 325 degrees Fahrenheit at 100 PSI of pressure. During the cycle, the wax melts and separates from the shell and is later collected and recycled for future patterns.

Next, the empty cavity, now free of most wax, is placed in a burnout furnace. Inside, the furnace reaches more than 2000 degrees Fahrenheit. It's so warm, employees working near the furnace must wear aluminized clothing to deflect the heat.

The burnout furnace serves several purposes. It burns off any residual wax and strengthens the shell. It also prevents shock when melted metal is poured into the cavity in the coming minutes. While the molds are in the burnout furnace, an hour-long process, 500 pounds of stainless steel is melted at 3000 degrees Fahrenheit.

After the shells are removed from the furnace, the liquid metal is poured inside the cavities from a ladle 50 pounds at a time. The process continues until all 500 pounds of melted metal are poured. Usually, that equates to 24 average propellers or 10 pod or Zeus-drive props.

Shells are then cooled on carts for about an hour before they are transferred to the cleaning cell, where residual ceramic is removed using three types of equipment - a knockout machine (resembling a jackhammer), an abrasive saw and a sandblaster.

By the completion of the process, the prop is free and clear of residual ceramic or oxidation. It is the last step of the casting process.

Now that the prop has been cast, machinists take over. Mercury's standard Delrin-sleeved props require minimal machining on the outside diameter of the hub. There is more extensive machining involved on props that counter rotate, like the Bravo Three.

Machinists have to work with the hub of the propeller and splines so the prop can affix to the prop shaft for these types of propellers.

Next, the propeller is transferred to the grinding department where grinders thin the leading edge of the blade and other areas of the prop that require sanding.

From there, the props go to the surface refinement area. For the next two hours, the props are placed in a drag finish machine to have their peaks and valleys sanded out of the propeller. The process creates a matte finish like Bravo Three or pod-drive props have. All other propellers go through a second refinement stage - burnishing - which creates a high-luster finish.

Finally, the prop is fitted with Performance Vent System plugs, which can be customized to deliver a better hole shot, and then is transferred to the boxing area to be boxed and delivered.