The Marinemaster

The Seiko Marinemaster 300 SBDX001 is a very rare watch that is a continuation of the lineage of real divers watches that Seiko began back in 1965. They first started with a 150m rated watch, but it did not take them long to double that to the 300m true diver rated watch we all know and love.

If you look at the watch without studying it in detail, you could mistake it in many ways for the cheaper and more common SKX range. But it is anything but.

The SBDX001 is built to last with its monobloc case, which has a flat back and no screw at all. It is super chunky at 15.7mm and only be accessed via the front. A smart design decision for a watch designed to be taken a little deeper than most divers do at 30m. Other than the rather oversized look of the case, it has brushed lugs that complement that otherwise polished look of the case and strap.

The dial is typical Seiko diver all around with large round pips, lavishly coated in Lumibrite, so easy to see in the dark. There is a simple date window at 3 o’clock, and the Marinemaster Professional 300m inscription at 6 o’clock. The crown is offset at 4 o’clock, which is not unusual for a diver, offering some sort of protection. However, it is disappointing to see no crown guard on a watch of this caliber!

And speaking of caliber, the movement is an 8L35, an undecorated and unadjusted version of the high-end Grand Seiko 9S55. Rhodium-plated, 26 jewels, automatic, 28800vph (4Hz), handwind and hacking, 50 hour power reserve. The size of the balance wheel was increased to provide the torque required, as the hands are heavier than a dress watch. The 8L35 is also used in the Landmaster, which has the same hands.

The movement by all accounts keeps excellent time, and in 9S55 trim is capable of exceeding COSC specs. Anecdotal reports on various fora indicate less than five seconds’ daily error is typical. The spec is -10 to +15 seconds per day.The 8L35 is completely in-house Seiko, and is descended from the 6159 300m diver, circa 1969. Everything from oil on up, including mainspring, is Seiko. Kinda cool. What they call a ‘manufacture’. John Davis is a big fan of the 8L35, and had this to say about it: the Seiko 8L35 is pretty much the same movement as the 9S55, but perhaps missing a few refinements and not as thoroughly adjusted. As such, it is one of the finest automatic movements Seiko makes. The machining is of the highest quality and the design and construction is informed by Seiko’s many years of experience.