One of the most common and expensive failures in high-performance boating is propeller loss caused by the prop nut backing off under load.
Whether running a Mercury Racing 250XS, 300X, 300XS, 300R, 400R, 450R, 500R, 2.5 EFI, 280 ROS, 300 Drag, or a high-horsepower offshore catamaran, vibration, surfacing conditions, cavitation, and rapid acceleration place enormous stress on traditional propeller retention hardware.
To solve this problem, Hill Marine developed the new patent-pending Split-Loc Propeller Nut (3/4-20"), now offered by Buckshot Racing #77 for serious performance boaters demanding maximum reliability and security on the water.
The Weaknesses of Traditional Nyloc and Spring Washer Systems
For years, Mercury Marine used traditional tab washer locking systems that created a very positive mechanical lock between the propeller nut and washer. While highly effective, the design required additional hardware and installation steps.
Over time, Mercury transitioned many newer applications to spring washer-style retention systems. Spring washers simplify installation, but they rely primarily on clamp load and friction tension to keep the nut tight.
In high-performance boating applications, repeated torque cycling, surfacing propeller operation, offshore vibration, cavitation loading, and rapid acceleration can gradually reduce spring washer preload. As preload decreases, the propeller nut can begin loosening over time.
Traditional Nyloc nuts face similar limitations. While the nylon insert helps resist rotation initially, repeated servicing, heat cycles, vibration, and extreme torque loads can reduce its holding effectiveness, hence the FAA guidance and repeat-use restriction on aircraft.
This becomes especially problematic on high-horsepower Mercury Racing platforms, where driveline shock loads are significantly higher than standard recreational boating environments.
Why Double-Nut Systems Often Fall Short
Some manufacturers attempted to improve propeller retention using double-nut systems. While the concept sounds effective, most marine propeller applications do not allow a true mechanical double-nut locking procedure.
For a double-nut system to work correctly, the first nut must be held stationary while the second nut is tightened against it to create opposing thread pressure between both fasteners.
On most overhub and through-hub propeller applications, there simply is not enough rear access behind the propeller to properly counter-hold the primary nut. In many cases, the second nut functions more like a simple jam nut rather than creating a true locking effect.
Under extreme marine vibration and repeated torque loading, this can still allow gradual loosening.
How the Split-Loc System Is Different
The Hill Marine Split-Loc was engineered specifically to eliminate the weaknesses found in spring washer systems, nyloc nuts, and traditional double-nut setups.
Unlike systems that rely mainly on preload tension or nylon friction, the Split-Loc creates an integrated mechanical locking effect directly against the propeller shaft threads.
As the nut is tightened, the internal locking geometry intentionally conforms to the shaft threads, increasing resistance to loosening caused by vibration, harmonics, cavitation events, and rapid torque changes.
The design functions similarly to a Stover-style prevailing torque lock nut, but is engineered specifically for extreme marine driveline loads and surfacing propeller applications.
The result is a more secure locking system capable of maintaining holding power under the severe conditions encountered in modern high-performance boating.
Engineered for Modern Mercury Racing Platforms
The Split-Lok Propeller Nut is designed for Mercury V6, V8, and V10 outboards along with high-performance sterndrive applications using 15-spline, 19-spline, and 23-spline propeller hubs.
Applications include many popular Mercury Racing and performance platforms including the Mercury Racing 300R, 400R, 450R, 500R, 2.5 EFI, 280 ROS, 300 Drag, 300X, and 300Xs along with offshore catamarans, surfacing-prop center consoles, poker run boats, bass boats, and high-performance pontoons.
This broad compatibility makes the Split-Loc ideal for both recreational and competitive high-performance boating environments.
Built for Extreme Marine Conditions
The Split-Loc is manufactured from high-quality marine-grade materials selected specifically for corrosion resistance, durability, and repeated service use in harsh marine environments.
Its precision-machined compact design delivers a clean, high-performance appearance while providing long-term reliability under severe offshore vibration and high-load operation.
Unlike disposable locking systems that degrade after repeated use, the Split-Loc is engineered for repeatable installation and removal while maintaining consistent locking performance.
Proven Through Extensive Testing
Before release, the Split-Loc underwent years of development, redesigning, and confidential testing across multiple marine platforms. Testing included high-horsepower tritoons, offshore catamarans, center consoles, and surfacing-prop applications operating under severe marine conditions.
The Split-Loc consistently demonstrated improved retention and resistance to loosening compared to traditional propeller retention methods