My Eastern Watch Collection: Seiko Prospex SFK003J1 Sea Sumo Solar GMT Green (similar to SFK001J1) - Additional Benefit of Solar and GMT, A Review (plus Video)

After launching a number of watches with just minor changes from previous offerings, earlier this year Seiko presented a new refreshing watch with a number of firsts. Based on the common "Sumo" design, these new SFK series uses a new movement that is both solar-powered and features a true GMT (i.e. local jumping hour) function.

As usual, there wasn't any fanfare for the launch. The market only started to noticed when bloggers and watch journalists started to write about it. To be honest, I only found out about it mid-February 2023. Even then, the Seiko website for the Malaysia region does not list the watch. Nevertheless, the global Seiko website has the watch listed. Meanwhile, the watch is now available at all the dealers in Malaysia.

I already have the SBDC003 (the first generation Sumo) and the SPB103J1 (the third generation Sumo). To be honest I am not sure whether we can quantify the SFK003J1 as the fourth generation Sumo. Despite it having similar shape, dimension and concept (diver watch), the use of a different type of movement and having an additional GMT function may put this model in a class of its own.

The Series

Seiko current has four models under the series. However, in any of the selling jurisdictions, you can't find all four models as Seiko splits it either in a set of twos or threes. For example, for Malaysia, you can only find two of the models, the SFK001 and the SFK003. Interestingly, all the models in the series are made in Japan, hence the 'J1' reference at the end of the 'SFK' reference. The reference 'SBPK' are JDM models.

SFK001J1 MSRP: RM3,600	SFK003J1/SBPK001 MSRP: RM3,600/YEN89,100
SBPK003 MSRP: YEN89,100	SBPK005 MSRP: YEN89,100

The Watch

Made out of 316L stainless steel, it is layered with Seiko’s proprietary super-hard coating and has alternating polished bevels and brushed lines. The case measures 45.0 mm in width with a lug-to-lug length of 51.8 mm. Generally similar in dimensions to the third generation mechanical Sumo except for the thickness where the newer Sumo is about 1.0 mm extra or 13.2 mm in height. The additional height is to accommodate the fourth hand (the GMT) on the central timing stem. Coupled with a stainless steel bracelet with the same super-hard coating, the whole package weighs in at 182 gm.

The sloping chapter ring on the SFK003 is painted in two set of colours minus the wave pattern. The top half is painted in muted lime green to signify the morning hours while the bottom half is painted in a darker green shade to signify the night hours. Also on the chapter ring are minute and hour markers in white.

The dial is slightly different than the chapter ring. The surface is micro grained with a fine horizontal wave pattern and coloured with a deep forest green hue. Apart from the applied hour markers painted with LumiBrite paint, in-between them are Arabic numbers printed in white to help track the GMT functionality. It is unfortunate that the 3:00 applied hour market had to be truncated to fit in the date aperture.

There are five lines of texts and logo as can be seen on the dial. The applied brand name is located at the upper quadrant. In the bottom quadrant one can see the Prospex logo, the words "GMT", "DIVER'S 200M" and a series of small prints of code at the bottom edge of the dial. Only the word "GMT" is in orange while the rest are printed in white.

As highlighted earlier, the date aperture is located at 3:00. There is no framing along the edge of the aperture. As the aperture requires the 3:00 hour marker to be truncated, the white background date wheel is supposed to minimize the visual disruption somewhat.

The hands are classic Sumo styling. The hours and minutes hands are sword-like and painted with LumiBrite. The seconds hand has a painted lollipop end with LumiBrite. The fourth hand is the GMT hand and designed like an arrow. This hand is printed in orange to differentiate it from the rest and part of the arrowhead is painted with LumiBrite as well.

Protecting the dial is a flat sapphire crystal with anti-reflective coating on the inner surface.

The uni-directional bezel has a 120-click gradation for a complete rotation. The system is as per Seiko standard, solid with practically no interplay. The aluminum insert has a kink at the inner edge where minute markers painted in white are set. On the main surface of the insert are a series of Arabic numbering and lines in white that ends at a luminous pip at 12:00. The insert is painted in emerald green.

Like before, the large screw-down unsigned crown is located at 4:00. There is no side protection provided for the crown. As a comment, I would have preferred if Seiko had the crown signed with the brand logo like the first Sumo with a nice 'S' stamped on the top surface (subsequent to the first series, the crown was unsigned).

The photo above also clearly shows why the Sumo, despite its dimensions, sit perfectly on the wrist. The inward curving 20.0 mm lugs follow the shape of wrists and coupled with the pass-through lug holes, strap replacement is much simpler.

The casing is paired by a traditional Seiko three-row link stainless steel bracelet secured by a three-fold clasp with push button release and a secure lock. There is also a simple extender for diving.

The watch has a screw-down case-back that is solid with a the standard tsunami logo etched in the center. Based on the serial number, this particular watch was made in October 2022.

Powering the watch is the brand-new Calibre 5K56 movement. This movement uses the solar-quartz technology. This 3-jewel in-house movement has a power reserve of approximately nine months and accuracy of +/- 15 seconds a month. The movement controls the 3-hand watch function, the true or traveller's GMT function and the date function.

The GMT hand refers to the base time and the normal hour hand is tied to the local time. If your base in Kuala Lumpur and you are in Kuala Lumpur, you should adjust the GMT hand and the hours hand to be the same. However, if you travel to London, when you adjust the time, you can easily move the hours hand by 8 hours without disturbing the minutes and seconds hands. Moreover, the movement of the date is tied to the local hour hand so you can correct the date in either direction if needed. Now, the GMT shows the time in Kuala Lumpur while the hour hand shows the time in London.

Below is a PDF of the manual for the Calibre 5K56 movement.

Seiko 5k65 Manual

Seiko does not disappoint when it comes to the illumination on the watch. Like all Prospex watches, this Sumo GMT is covered in LumiBrite paint and below is a photo to show how bright the watch is in the dark.

The Wearing Experience

This watch wears like any Sumo that came before it. What it has that is better is the adoption of the solar powered movement.

Solar power is a positive development as it reduces the anxiety of the user to ensure there is power available in the watch. What I mean by this is that generally, mechanical powered Sumo has a very limited power reserve of approximately a few days (50 hours for the 6R15 movement and 70 hours for the 6R35 movement). As such, you need to get it moving ever so often to not run out of power. In the case of the Sumo Solar, it can be on standby at least 9 months sitting quietly on the table and in the dark. If there is any light source present, it is sufficient to trickle charge the battery indefinitely.

Specifications

Case Material: Stainless steel
Thickness: 13.2 mm
Diameter: 45.0 mm
Lug-to-lug: 51.8 mm
Lug Width: 20.0 mm
Crystal: Sapphire crystal with anti-reflective coating on inner surface
Illumination: LumiBrite on hands, indexes and bezel
Clasp: Three-fold clasp with secure lock, push button release with extender
Bracelet Length: 200.0 mm
Water Resistance: 200 m / 660ft; diver's certified
Magnetic Resistance: 4,800 A/m
Weight: 182.0 gm
Caliber: 5K65

Movement Type: Solar

Precision: ±15 seconds per month

Jewels: 3

Power Reserve: Approximately 9 months

Functions: Overcharge prevention function; Quick-start function; GMT hand; Date display

Features: Unidirectional rotating bezel; Screw-down crown; Screw-down case-back

Launch Date: 2023

MSRP: RM3,600

Vendor: AWG, Mid Valley

Purchase Date: 27 February 2023

Purchase Price: RM2,700

Serial Number: 2O1562