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[A-PEN68 Development Log] Episode 10: Deepening Development and Innovation in Internal Structure

  • Writer: R.Nakanishi
    R.Nakanishi
  • Apr 17
  • 6 min read

From A-PEN 65 to A-PEN 68: A Complete Structural Overhaul

The A-PEN 68 isn't just a slightly larger version of the 65. When scaling up from 65mm to 68mm, we completely re-engineered the lure from the ground up. To put it simply, while it inherits the core action DNA of the original A-PEN 90, the 68 features a streamlined, ultra-efficient internal redesign.

Stripping It Down: Maximizing Buoyancy

Why simplify the internals? Because maximizing air capacity is the absolute fastest way to boost buoyancy. In hardbait design, every extra internal wall or chamber reduces the air pocket and kills buoyancy. It’s an unavoidable law of physics.

With the A-PEN 68, we stripped away the clutter, pushing the internal composition as close to "pure air and raw ballast" as possible.

Key Takeaway: By eliminating non-essential internal structures, the A-PEN 68 achieves maximum air volume for an incredibly agile topwater action.

Rethinking Lure Design: Balancing Buoyancy and Center of Gravity

Traditional hardbait design often obsesses over one question: "How much weight can we cram inside?" However, this approach usually ignores the critical relationship between buoyancy and the center of gravity.

As we noted in our ZELPHAS Development Logs (Episode 2), wall thickness and internal structures directly impact air capacity and floatation. The A-PEN 68 challenges conventional design by eliminating everything but the absolute essentials.


Engineering the Inside: Protecting the Air Pocket


Throughout development, our core philosophy was clear: Do not sacrifice air volume. Every minor detail was scrutinized to preserve space inside the bait:

  • Minimalist Rattles: Reduced the internal chamber wall to the bare minimum needed to secure the front rattle.

  • Ω-Shaped Belly Eye: Swapped traditional hardware for an Omega-shaped wire eye to free up internal air space.

  • Shortened Sound Rail: Scaled down the travel rail for the one-knock rattle to the absolute minimum.

  • Pin-Fixed Main Ballast: Secured the primary rear weight with a minimalist pin structure rather than solid plastic walls.

Every single tweak serves a single purpose: maximizing internal air volume. Innovation in Weight & Hardware Placement

The Pin-Fixed Ballast System

Typically, the rear main weight of a topwater walking bait is completely enclosed by plastic walls. The A-PEN 68 tosses that rulebook out. By using a precise pin-locking system instead of a full chamber, we reclaimed a massive amount of internal air capacity.


To minimize internal structure and increase airflow, the front hook uses an Ω-shaped wire.
To minimize internal structure and increase airflow, the front hook uses an Ω-shaped wire.

The Omega ($\Omega$) Wire Hook Eye

We also re-engineered the front hook hanger. Instead of a standard heavy figure-eight eyelet, we utilized an Omega-shaped wire. This low-profile hardware keeps the internal area around the hook hanger clear, packing even more air into the front section of the bait.

The Ultimate Balance

By stacking these microscopic gains, we achieved a high-buoyancy body paired with optimized internal ballast. By managing the overall specific gravity rather than just the weight, we unlocked effortless walking action and rock-solid casting stability.

The result? A compact topwater bait that casts like a bullet but sits perfectly high in the water column.

The On-Water Feel: Balsa Responsiveness Meets ABS Sound

Thanks to this structural redesign, the A-PEN 68 boasts far greater buoyancy than standard plastic topwaters. This allows us to place a heavier weight inside a lighter shell. On the water, this translates to the hyper-responsive, crisp walking action typically found only in premium balsa wood lures. Balsa Physics × One-Knock Acoustic

To get a nimble, instant-start action in a 68mm profile—while retaining the hard-hitting sound only plastic can provide—high buoyancy was non-negotiable.

Balsa cannot produce that crisp, resonant "clack" of a one-knock rattle. By re-engineering the internal architecture of an ABS body, we successfully packed both worlds into a compact 68mm frame.

Even with the same shape and total weight, a lure with a light body and heavy weights, or a lure with a heavy body and light weights, will be a completely different lure. The difference in specific gravity of wooden lures clearly demonstrates this.
Even with the same shape and total weight, a lure with a light body and heavy weights, or a lure with a heavy body and light weights, will be a completely different lure. The difference in specific gravity of wooden lures clearly demonstrates this.

High-Density Hardwood vs. Ultra-Buoyant Balsa Feel

Of course, heavy, high-density wood walking baits have their own distinct advantages:

  • Substantial body weight for cutting through wind.

  • Heavy water displacement.

  • Easy, wide-gliding side-to-side action.

These are incredible traits, and the original A-PEN 90 was actually tuned closer to this heavyweight style (see A-PEN Development Secrets: Episode 3).

For the A-PEN 68, we wanted the exact opposite:

  • An ultra-lightweight body shell.

  • High riding buoyancy.

  • Instant, linear response to the slightest rod twitch.

If we had simply shrunk the A-PEN 90 design down to 68mm, it still would have been a good lure, but it wouldn't have had the right responsiveness for its size. Downsizing requires optimizing. The A-PEN 68 isn't just a smaller version; it's a hybrid evolution—combining the live-wire feel of balsa with the acoustic benefits of ABS.

The A-PEN90 is designed to target monster fish, and therefore, while increasing the body's strength, it also incorporates an increased internal structure to create water displacement similar to that of a high-density wooden lure.
The A-PEN90 is designed to target monster fish, and therefore, while increasing the body's strength, it also incorporates an increased internal structure to create water displacement similar to that of a high-density wooden lure.

Leaving the "Margin": The Final Tuning Space for Anglers

This is the most critical element of the A-PEN 68's design philosophy. During the final prototyping stages, we collaborated closely with elite anglers and pro staffs—including Top Butler, Flagship, TK Takuya, and Kita-san from North Wave.

We obsessed over the final weight balance down to the 0.1-gram level, testing how the slightest variance altered the bait's resting angle on the surface.

The final settings were the result of much deliberation.
The final settings were the result of much deliberation.

Tailoring to Your Local Fisheries

Through endless testing, one truth became undeniable: the perfect setup changes depending on the water.

Whether it is walking the bank at a local reservoir for largemouth bass, boat fishing on massive lakes, or targeting finicky saltwater species like bream (Chining) in tidal rivers and estuaries—different waters demand subtle tweaks.

The 0.1-Gram Decision

How do you mass-produce a lure when the "perfect" weight fluctuates by a fraction of a gram?

Our answer was simple: Don't force a single "correct" answer onto the angler.

If we locked the bait into one hyper-specific setting, it would underperform in other scenarios. Instead, we engineered a "tuning margin" directly into the product.

The "Tuning Margin" Philosophy

The factory A-PEN 68 is tuned to the ideal middle-ground balance. However, we left just enough buoyancy reserve so that anglers can apply 0.1g to 0.5g lead weight strips or dots to customize the lure's performance to their exact local conditions, water salinity, and target species.

The left shows the lure with the default #8 hook, and the right shows it with the included #6 hook. Both have enough room for weight adjustment.
The left shows the lure with the default #8 hook, and the right shows it with the included #6 hook. Both have enough room for weight adjustment.

High-Performance Out of the Box, Ready for Customization

Make no mistake—out of the package, the A-PEN 68 delivers elite performance. Thanks to its minimalist internals, it natively offers:

  • High-riding buoyancy

  • Concentrated center of gravity

  • Instantaneous walking response

  • Loud, hard-thumping one-knock acoustic

We simply left a little bit of "headroom" for the advanced angler.

Built to Handle Adjustments

The buoyancy profile is forgiving enough that adding a small amount of adhesive lead tape won't ruin the bait’s action. If you need it to ride lower to cut through chop or want a fraction more casting distance, the bait is designed to accept those modifications seamlessly.

Dialing in Your Line Setup

Topwater lures of this size are highly sensitive to line choices. Your action, dive depth, and pause recovery change drastically depending on whether you throw:

  • Braided line (PE) with a fluorocarbon leader (and varying leader lengths)

  • Straight Braid (PE)

  • Monofilament / Nylon

  • Straight Fluorocarbon

During our official testing, our benchmark setups were 12lb Monofilament and 0.8 Braid paired with a long 14lb Nylon leader. By engineering a performance margin into the hull, the A-PEN 68 maintains its fish-catching action across all of these line configurations.

The A-PEN68 was completed with enough leeway to accommodate various tackle settings.
The A-PEN68 was completed with enough leeway to accommodate various tackle settings.

The Final Touch Belongs to the Angler

We didn't lock the A-PEN 68 into an unchangeable, rigid setting. We left the final polish to you.

Use that built-in margin to make it cast further, dive slightly on the rip, or match the exact salt density of your local flats. Take your gear, head to your home waters, and tune the A-PEN 68 into your ultimate topwater weapon.

This buoyancy-first design philosophy is destined to become a core pillar of all future ADUSTA lure development.

In our next installment (Episode 11), we take the finalized production samples into the field for the ultimate showdown: Real-World Testing (Kansai Bass Edition). Stay tuned.


 
 
 

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