Sea-Gull M160S/M162S/M163S – 39mm Automatic Watch | ST25 | Sapphire
Mechanical watches are at their most interesting when you can actually see their inner workings. The Sea-Gull M160S, M162S and M163S take that idea quite literally, opening part of the dial to expose the moving balance assembly underneath, while surrounding it with additional calendar displays. The result is considerably more visually complicated than a conventional three-hand watch, but also much more effective at showing the workings inside an automatic movement.
The case measures 39mm across, which initially sounds relatively compact. However, the approximately 53.7mm lug-to-lug length is unusually long for a watch of this diameter, which gives the case considerably more presence on the wrist than the 39mm measurement alone might suggest. At approximately 13mm thick and around 150g on the stainless-steel bracelet, this is also a fairly substantial watch. It does not have the bulk of a large dive watch, but buyers expecting the lightness of a traditional 39mm dress watch may be surprised by how solid it feels.
Inside is one of Sea-Gull's ST25 family of automatic movements, with the exact calibre depending on the version. The M160S uses the ST2502, the M162S uses the ST2504 and the M163S uses the ST2505. All three are mechanical automatic movements produced by Sea-Gull itself rather than bought from a third-party movement supplier. Automatic means that the watch winds itself through the movement of your wrist, using a rotating weight inside the case to store energy in the mainspring. The ST25 family runs at 21,600 vibrations per hour, or six beats per second, producing the smoother stepped motion associated with a mechanical seconds hand. Sea-Gull quotes up to approximately 45 hours of power reserve for the ST25 family, although the exact figure can vary between individual calibres and configurations. This should be enough for the watch to continue running overnight and into the following day after being sufficiently wound. The number of jewels also varies between models; Sea-Gull lists 29 jewels for the M160S, 33 for the M162S and 38 for the M163S. Jewels are small synthetic bearings placed at points of friction inside a mechanical movement. A larger number does not automatically make one movement 'better', particularly when additional complications require more moving parts, but they form an important part of reducing wear within the mechanism.
The feature that gives this collection much of its character is the opening in the dial. Sea-Gull sometimes describes this as a 'flywheel', but the more useful term is open heart. It allows you to see the balance wheel oscillating backwards and forwards as the watch runs, providing an almost constant display of the mechanical movement underneath. It is important not to confuse this with a tourbillon, in which the escapement and balance rotate within a moving cage. Here, the balance mechanism remains in a fixed position and is simply exposed through the dial. This does not make it any less enjoyable to watch, but it is a fundamentally different complication.
The exact display arrangement varies between the M160S, M162S and M163S because each uses a different member of the ST25 movement family. The additional displays include calendar information, day indication and power-reserve information, which makes it worth checking the particular dial layout you prefer, rather than treating the three options simply as colour variations of the same watch. One of the interesting features of the more complicated layouts is that they show what mechanical watchmaking can do beyond simply moving three hands around a dial. Calendar displays and power-reserve indicators require additional gearing within the movement, making these considerably more mechanically involved than Sea-Gull's basic automatic watches.
Above the dial is synthetic sapphire crystal, which is significantly more resistant to everyday surface scratching than standard mineral glass and is particularly welcome here because there is considerable action happening underneath. Keeping the crystal clear helps preserve both the legibility of the calendar displays and the view into the movement. The case and bracelet are made from 316L stainless steel. The bracelet measures 20mm wide and is secured with a concealed push-button clasp, keeping the underside relatively clean when it is closed. Turn the watch over and the mechanical interest continues through an exhibition case back, which allows more of the ST25 movement to remain visible, including the automatic winding rotor and parts of the gear train that cannot be seen through the opening in the dial. When buying your first mechanical watch, I think there is genuine value in actually being able to see the dozens of component parts of the mechanism moving from both sides of the watch, as it makes the appeal of mechanical watchmaking considerably easier to understand.
Water resistance is rated to 50m, or 5 bar, which is suitable for rain, hand washing and normal everyday exposure to water, but this is not a watch I would choose specifically for swimming. Its complication-heavy design and smarter steel construction make it much more of an everyday mechanical watch than a sports or dive watch.
And that is really where this Sea-Gull collection makes sense. There are simpler automatic watches available for someone who only wants reliable mechanical timekeeping, but the M160S, M162S and M163S are about making the mechanism itself part of the experience. You can see the balance moving, view the movement through the back and interact with complications beyond simply setting the time. Sea-Gull also brings something important to the equation as a manufacturer. The company has been producing watches and mechanical movements since 1955 and manufactures the ST25 family itself, meaning the movement, complications and watch come from the same watchmaker rather than the case simply being built around an off-the-shelf Japanese calibre.
The obvious trade-off is visual complexity. There is considerably more information on these dials than on a conventional three-hand watch, and buyers who prefer clean, restrained designs may find the combination of open heart and additional calendar displays unnecessarily busy.
For someone who wants their first automatic watch to make mechanical watchmaking visible, however, this is a particularly interesting proposition. Sapphire crystal and stainless-steel construction provide the practical side, while the open-heart display, exhibition case back and Sea-Gull-built movement give you considerably more to explore than a conventional three-hander.
Included in the box:
Sea-Gull M160S, M162S or M163S automatic watch and Sea-Gull presentation box as supplied.
Worth knowing:
The three model numbers are mechanically different. The M160S uses the ST2502 movement, the M162S uses the ST2504 and the M163S uses the ST2505, with different jewel counts and complication layouts between them.
Although the case is only 39mm across, the approximately 53.7mm lug-to-lug length is unusually long. Combined with the approximately 150g weight, this means the watch will wear considerably larger and more substantially than the diameter might initially suggest.
