The Secret Story Behind the Development of the A-PEN ~Episode 3~
- R.Nakanishi
- Apr 28, 2020
- 4 min read
The Engineering Inside the A-PEN: Acoustics, Buoyancy Vectors, and Aerodynamics
By: Nakanishi, ADUSTA Lure Designer
Hey everyone, Nakanishi here, lead lure designer for ADUSTA.
In this blog series, I’m pulling back the curtain on the development stories, design concepts, and tuning secrets of the ADUSTA A-PEN.
For Episode 3, we are diving deep beneath the surface shell. Let’s look at the internal architecture, advanced weighting systems, and raw materials that make this 90mm topwater stickbait an absolute acoustic weapon.
1. The Multi-Tiered Internal Weight Configuration
The internal chambers of the A-PEN are engineered to produce a dual-sound frequency profile while optimizing castability and buoyancy.
High-Impact Tungsten Weight Transfer System
The defining characteristic of the A-PEN is its commanding "one-knock" acoustic signature. This is achieved by an internal Tungsten Weight Transfer System. During the retrieve, a high-density tungsten ball shifts back and forth, forcefully colliding with a massive steel ball locked securely in the extreme rear of the bait. Furthermore, during a cast, this tungsten ballast shifts completely to the rear tail section, acting as a kinetic weight transfer that maximizes casting distance and punch.
Fixed Steel Tail Ballast
A large steel weight is permanently anchored into the rear of the bait. This fixed ballast establishes the A-PEN's signature tail-down resting posture. This angle keeps the tail pinned in the strike zone and makes it incredibly easy for any angler to execute a perfect walk-the-dog cadence right out of the box, ensuring maximum versatility across multiple retrieval styles.
High-Pitch Micro Rattle Chamber
In addition to the heavy low-frequency one-knock sound, we engineered a dedicated High-Pitch Rattle Chamber into the nose section of the bait. This chamber houses two miniature steel balls and two glass beads. With every single twitch of your rod tip, this combination generates a high-frequency, crisp clicking sound that perfectly mimics the panicked clicking of fleeing baitfish.
2. Hydrodynamic Body Geometry & Surface Displacement
The Triangular Cross-Section
The A-PEN features a distinct, modified triangular (or "onigiri" rice-ball style) cross-section. The bottom of the bait is engineered with a wide, flat belly that creates immense surface displacement and hydro-acoustic waves, giving this 90mm profile the drawing power of a much larger lure.
This flat belly also serves a structural purpose: it acts as a planing surface during a power-skate retrieve, allowing the bait to execute long, sweeping side-to-side glides. Conversely, the sides and back taper smoothly upward into a rounded ridge. This geometry forces the bait to roll slightly during its walk, exposing its flanks to create a high-vis flash and strobe effect that triggers reaction strikes from deep below.
Internal Structural Bulkheads & Truss Matrix
Topwater baits take absolute punishment from violent blowups and heavy cover impacts. To guarantee structural integrity, we designed an internal truss partition matrix (reinforcement bulkheads) inside the ABS shell.
Beyond structural rigidity, this added internal material thickness increases the overall specific gravity of the lure. This allows the A-PEN to sit slightly deeper in the surface tension, wrapping itself in water just like a traditional wooden topwater plug for a more organic presentation.
3. Material Science: Bone ABS vs. Clear ABS
We offer the A-PEN in two distinct plastic compound formulations depending on your tactical acoustic needs:
Material Type | Color Palette | Acoustic Property | Tactical Application |
Bone ABS (Natural ABS) | Solid / Opaque / Metallic | Loud, High-Pitch "One-Knock" | High appeal, muddy water, high wind, or aggressive species like Amazon Peacock Bass. |
Clear ABS | Transparent / Ghost / Translucent | Muted, Deep "Thud" Sound | Stealth approaches, calm slick water, highly pressured fisheries, or clear lakes. |
The Bone ABS formulation is the heart and soul of the A-PEN concept. This specific resin is much harder and more resonant than standard clear plastics. When the internal tungsten ball strikes the rear steel ballast, the Bone ABS amplifies the shockwave, sending a piercing, high-frequency knock through the water column. This aggressive acoustic resonance was precisely what Amazonian Peacock Bass demanded during our jungle testing phases.
Conversely, the standard Clear ABS resin absorbs a portion of the impact energy, outputting a softer, more subtle acoustic signature—perfect for spooky fish under clear skies.
Visual Design & Baitfish Replication
The facial structure of the A-PEN is modeled after ubiquitous baitfish species like small wild carp, shiners, and minnows, ensuring it looks natural to predatory fish anywhere in the world. We also oversized the eye sockets to serve as a prominent strike marker, giving tracking predators a clear focal point to strike, which drastically optimizes your hook-up ratio.
4. Field Testing & The Final Prototyping Phase
During R&D, we manufactured dozens of unique internal configurations. Some prototypes were heavily tail-weighted purely for maximum casting distance; others prioritized an ultra-wide diving walk at the expense of casting stability.
We handed these variations over to our international pro staff for rigorous evaluation. While it was difficult to choose between our extreme long-distance diving models and our tight-walking variants, our field testers overwhelmingly favored the Balanced Prototype Platform. This final production setup achieves the absolute golden ratio between maximum casting distance, immediate startup response, and raw acoustic appeal.
The Global Verdict: Taming China’s Skygagers
Following its official global launch, the A-PEN received massive acclaim from an unexpected fishery: China.
Bank anglers across China's massive public waters have heavily adopted the A-PEN for targeting giant Skygagers (an aggressive pelagic predator similar to the cultus/predatory carp that can exceed 1 meter in length). Because Skygager fishing is predominantly done from the shore across vast, open expanses of water, extreme casting distance is paramount.
Chinese anglers have given the A-PEN premier ratings due to its incredible aerodynamics and high-density internal weighting, allowing them to hit distant surface schooling fish that standard topwater plugs simply cannot reach.
In our next entry, Episode 4, we will break down the exact operational mechanics of the A-PEN, including tactical rod movements, best-in-class tackle matchups, and custom trailer hook modifications.
Stay tuned!
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