The fish fin and ballast system is essential for keeping the underwater camera stable and maintaining a precise viewing angle. Based on the installation steps and the plumb-bob hanging diagram, here is the correct procedure for assembling and using the fin.

1. Five-Step Fin Installation

Step 1: Thread the Main Line
Pass the main fishing line through the line guide hole at the rear of the fin. This secures the line to the fin and prevents detachment during casting or under current pressure.

Step 2: Slide on the Soft Rubber Fin
Align the black soft-rubber fin with the slot or rail on the camera body and slide it toward the tail until it stops and no longer moves. The soft material cushions impacts and provides hydrodynamic stability.

Step 3: Lock the Buckle
Once the fin is fully seated, make sure the small protrusions on both sides of the camera line up with the corresponding recesses in the fin. Press the locking buckle until you hear an audible “click”. Always confirm the buckle is fully closed; this is critical to prevent the fin from coming off underwater.

Step 4: Attach the Ballast Weight
Take the ballast weight and metal hook shown in the image. Align the hanging hole of the weight with the pre-drilled hole at the bottom of the fin, and secure it with the hook. The weight adds tail ballast, helping the camera sink quickly and maintain a downward-facing viewing angle.

Step 5: Final Grip and Check
After installation, hold the camera by the metal guide hole or the main line and gently shake it to check that the fin, weight, and camera body are all firmly connected. Once confirmed, the unit is ready for deployment.

2. Plumb-Bob Hanging and Angle Adjustment

The “Plumbum hanging figure” on the left illustrates the core function of the ballast system. The weight hangs below the fin via the hook, using gravity to straighten the main line and stabilize the camera’s posture. In practice, choose a weight suitable for the water depth and current: use a lighter weight in still, shallow water and a heavier one in deep or flowing water to ensure the lens consistently faces the intended direction (e.g., straight down or angled forward).

3. Usage Notes

• Pre-Dive Inspection: Before each use, confirm the buckle is locked and the weight is securely attached to avoid losing parts underwater.

• Avoid Forced Removal: When detaching the fin, always open the lock first before sliding it off. Pulling it off directly may damage the buckle or the soft fin.

• Adjust Ballast for Current: In faster currents, increase the weight or adjust the angle of the guide hole to keep the camera stable.