Hands-on: Seiko launches new solar-powered GMT movement in blue-green sumo style

Text/image: Ola Jacobsen

Yesterday Seiko released a new version of its well-liked so-called Sumo. Two 45 millimetre steel divers with blue and green dials. But the big news is the orange GMT hand – and the solar-powered movement that drives it. 

Seiko does everything in-house. From growing their own quartz crystals to hairsprings, cases and blued hands. That is why a new movement from Seiko is perhaps not so remarkable. The movement list on their website is already several hundred lines long. But for those of us who are amused by well-designed, functional and good-value watches that do not shy away from a decent adventure, today's news bodes well. 

The release consists of two versions. The blue Seiko Prospex Scuba Solar GMT SFK001 has a dark blue rotating bezel, a lighter blue dial with a fine woven horizontal pattern and, a blue/light blue chapter ring with day and night marking. 

The Seiko Prospex Scuba Solar GMT SFK003 matches a darker blue-green dial with the same horizontally woven pattern with a bright green rotating bezel and a dark green/lime green chapter ring for day and night marking. 

Both references have the same tastefully judged orange GMT hand and both wear, just like many other divers from Seiko, smaller than their dimensions.

The so-called sumo case is a somewhat flattened version of the case on the iconic diver's watch 6159–7000 from 1968. Besides being good-looking, the magical design is also good at hiding its dimensions, both to the eye and to the feel on the wrist. A Seiko diver with this case type looks and wears like a Swiss equivalent several millimetres smaller with straight case sides. 

Both the SFK001 and the SFK003 are fine watches. Especially the blue one on the SFK001 is exactly the type of well-tuned subtle dials that Seiko has been so good at since the 70s. In many lights you do not even notice that the dial is patterned, but in a certain position it emerges and in one stroke pushes the watch into a whole new dimension. But as I have touched on, today's news in the first instance not about these two watches, but about the new movement that drives them. 

For the first time Seiko has, with the launch of the Solar 5K65, a solar-powered movement with a GMT complication. Seiko struggled for a long time with its so-called Kinetic movements. Battery-driven quartz watches that were charged by the wrist movment via a rotor as on mechanical automatic movements. 

The idea with both Seiko Kinetic and Solar is that you should get the quartz movement's advantages in the form of reliability, exact timekeeping and relative freedom from maintenance, but without ever having to change a battery. 

In recent years the solar-powered technology has taken over more and more in Seiko's catalogue of quartz watches that do not require a battery change. This solar-powered GMT movement may be the death blow for the Kinetic era. Who is going to say no to a GMT movement with nine months of power reserve, which charges fully in 15 hours in strong sunlight? 

I believe that the automatic GMT movement 4R34 which was launched in the Seiko 5 GMT last year and the new Solar 5K65, will be used in a range of entry-level and mid-price models. 

In summary: Prepare yourself for even more good-value GMT watches from Japan. The year is young and I would not be surprised if we get to see this movement in more cases before it is over.

Technical specifications

Brand: Seiko
Model: Prospex Scuba Solar GMT 
Reference number: SFK001 (blue), SFK003 (green)

Diameter: 45 mm
Thickness: 13,16mm
Length: 51,8mm
Water resistance: 200 metres

Case material: Steel
Dial: Blue or green, patterned
Bracelet: Steel bracelet

Movement: 5K65, in-house Seiko
Functions: Hours, minutes, seconds, date, GMT
Accuracy: ± 15 seconds a month
Power reserve: 9 months
Winding: Solar-powered, fully charged after 15 hours in strong direct sunlight

Price: 8,998kr
In shops: In February 2023