The Seiko 8M18A is a specialized digital quartz movement developed for sailing and regatta race timing. Designed for functionality, clarity, and reliability, the 8M18A features a programmable countdown timer, audible alarms, and automatic start-to-chronograph switch once the race begins. Unlike analog yacht timers, this caliber provides a purely digital interface, making it highly legible and precise under demanding marine conditions.

It was primarily used in Seiko’s Prospex Yacht Timer models, especially during the early 2000s, and is now valued among sports watch collectors and professionals.

Technical Specifications

• Caliber Number: 8M18A

• Movement Type: Quartz (Digital LCD)

• Primary Functions:

  • 12/24-hour timekeeping

  • Programmable countdown timer (1 to 10 minutes)

  • Automatic switch to chronograph after countdown

  • Alarm (daily)

  • Stopwatch (up to 99 minutes 59 seconds)

  • Audible buzzer with pre-race alerts

• Display Type: 3-field digital LCD

• Battery Type: CR2025 (3V lithium coin cell)

• Battery Life: Approx. 5 years

• Accuracy: ±20 seconds per month

• Water Resistance: Case-dependent (usually 100 meters or more)

• Module Size: Compact rectangular format for case integration

Key Features

Countdown Timer for Regattas

The centerpiece of the 8M18A is the programmable countdown timer, designed to assist sailors during the critical minutes leading up to a race start. Users can set the timer in 1-minute increments from 1 to 10 minutes.

• Emits audible beeps every minute during the countdown

• Emits one beep per second in the final 10 seconds

• Automatically switches to chronograph mode when the countdown reaches zero

• Helps skippers track both pre-start and race time without manual reset

Chronograph Function

Once the countdown completes, the 8M18A continues tracking elapsed time with its stopwatch mode.

• Measures up to 99 minutes 59 seconds

• Useful for tracking overall race time or intervals during racing

Timekeeping and Alarm

• Displays current time in either 12-hour or 24-hour format

• Includes a daily alarm function with buzzer

• Hourly chime available in some versions

Display Layout

The LCD screen of the 8M18A is split into multiple sections for simultaneous visibility of:

• Current time or stopwatch

• Countdown timer

• Alarm or mode indicators

Some models include additional icons for chime and alarm status.

The layout is built for instant readability, especially important in outdoor or marine environments.

Button Functions

Most watches powered by the 8M18A have four external pushers, arranged as follows:

• A (Top Left): Mode button – cycles between Time, Timer, Chronograph, and Alarm

• B (Bottom Left): Set or recall – initiates setting or clears/reset values

• C (Top Right): Start/Stop – used for timer and chronograph

• D (Bottom Right): Adjust – changes values or toggles settings

These buttons are designed to be large and accessible, even while wearing gloves.

Setting Instructions

To Set the Time

1. Press A to enter Time Mode

2. Hold B until the seconds start flashing

3. Use D to adjust the value

4. Press B again to cycle through hours, minutes, and 12/24-hour format

5. Confirm by pressing A

To Set the Countdown Timer

1. Press A to enter Timer Mode

2. Hold B until the countdown value flashes

3. Use D to set desired minutes (1–10)

4. Press B to confirm

5. Use C to start/pause the countdown

6. Use B to reset if needed

To Use the Chronograph

1. Press A to enter Chronograph Mode

2. Press C to start and stop

3. Press B to reset to zero

To Set the Alarm

1. Press A to enter Alarm Mode

2. Hold B until hour flashes

3. Use D to adjust, press B again for minutes

4. Press B again to toggle alarm ON/OFF

5. Confirm with A

Battery Replacement and Reset

Battery Type:

• CR2025 lithium coin cell

• Lasts approximately 5 years under normal use

Reset Procedure After Battery Change:

1. Replace battery using non-metallic tweezers

2. After installation, use metal tweezers to short the AC terminal (marked on PCB) to the battery’s negative terminal (case or spring)

3. Hold for 2–3 seconds

4. The display should flash and reset

5. Reprogram time, timer, and alarm as needed

Maintenance Notes

• No lubrication or mechanical servicing required

• Clean contact points on the battery and springs before closing the case

• Replace gaskets and test water resistance during battery service

• Avoid strong shocks and prolonged exposure to saltwater

• Rinse after sea use and store dry

Watch Models Using 8M18A

The 8M18A movement was most commonly used in:

• Seiko Prospex Yacht Timer models

• Seiko Marine Master Regatta Digital series

• Models typically feature resin or stainless steel cases, rubber straps, large pushers, and 100 m or more water resistance

• Popular reference numbers include SBBN027, SBBN029, and similar early 2000s regatta models

Summary

Conclusion

The Seiko 8M18A is a reliable and efficient digital yacht timer movement built for competitive sailing environments. With its precise countdown function, auto-switch to chronograph, and audible alerts, it serves as a specialized tool for skippers and race crews. Rugged, legible, and easy to use, it remains a valuable companion both on and off the water for those who appreciate purpose-driven watchmaking.