Weekly Watch Photo – Seiko Marine Master 300

The Seiko Marine Master 300 is Seiko’s high-end alternative for Rolex sportswatches. This might sound like a bold statement, but those who know this Seiko, will agree. The Weekly Watch Photo is made by Tony.

Again a Seiko as our Weekly Watch Photo, but something different than the Samurai we post earlier this month. Tony has a very nice blog about his watch collection and he puts much effort in keeping it stylish. He posted his Marine Master 300M on his own blog, called halfpastthehour. Let us give you some more information about the Seiko Marine Master 300 or MM300 as it’s nicknamed by collectors.

This is no ordinary Seiko; this Marine Master 300 is part of the ‘Prospex’ line of watches, Seiko’s upscale diver line that is only sold and marketed in Japan. There is another Marine Master in the Prospex line, but that one has a depth rating of 600 meters and has a spring drive movement. This Seiko Marine Master 300 is reference number SBDX001.

Most dive watches designed for depths of 300 meters, like the Rolex Sea-Dweller or Omega Seamaster, are equipped with a helium/gas escape valve. Due to the superior seal this Seiko doesn’t need a helium/gas escape valve.

The design is based on a more than 30-year old design, however everything is bigger and more robust compared to older (and most other) Seiko dive watches. With a height of 14.6 mm and a diameter of 44 mm, and weighing 209 gr on the bracelet (136 gr on the rubber strap), the monocoque case still wears comfortable.

The movement is caliber 8L35, which is an undecorated and unadjusted version of the high-end Grand Seiko caliber 9S55. It’s rhodium-plated, has 26 jewels, beats at 28,800 vph (or 4 Hz), has 50 hours of power reserve, has a hacking function and has automatic winding. Compared to caliber 9S55 this caliber 8L35 has an increased balance wheel. Although Seiko says it’s regulated to -10 and +15 seconds, most owners report a daily deviation of well within COSC specifications.

This Seiko movement does not seem to be hand-finished, so no beveled edges but machine finishing. The dial is matt black and features applied indices and Seiko’s magnificent Lumibrite fill on markers and hands. Lumibrite is Seiko’s own variant of Super Luminova.

Make sure to check out Tony’s blog halfpastthehour.

Frank Geelen

Frank Geelen is an expert on Haute Horlogerie and his horological heart beats faster from beautiful hand-finished mechanical movements. He loves to explain all technical details of complications like tourbillons, minute repeaters, constant force escapements and column-wheel chronographs and he has been doing that for more than seven years. Besides publishing daily here at Monochrome Watches, Frank also writes for several other publications, both online and offline.

View all articles by Frank Geelen

2 Responses to “Weekly Watch Photo – Seiko Marine Master 300”

  1. Tony says:

    Thanks very much for posting my photos, and a link to Half Past The Hour. Very flattered to have been featured :)

  2. mono says:

    Well thank you for letting me use those beautiful photos Tony!

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