The Seiko Marinemaster line; What’s the difference?

The Marinemaster line has always been in Seiko’s upper echelon of divers. With prices for the fully speced and sized Marinemaster 300 starting at well over $4000, they’re certainly asking for big money for what is, to the untrained eye, a mere ‘Japanese watch’. But the Marinemaster 300 is a true beast of a watch, both on the spec sheet and in person.

Over the years however, Seiko has released other variations of the Marinemaster: the limited-edition diver’s 55th anniversary MM300 with a monobloc case and a whacking great 8L55 Hi-beat automatic caliber; the 1968 diver’s recreation; a baby version of the 55th anniversary with a 6r35 movement instead of the Hi-beat; and of course, the Baby Marinemaster AKA the MM200, which is what we’ll be looking at today alongside the MM300.

We’ll be comparing this pair of rather fantastic divers (in their respective price points) and be taking a look at what makes them tick, and why two watches of rather similar name and with a mere 100m of water resistance in difference can result in a price difference between each other of over $2000. Well, without further ado, let’s find out.




Seiko first introduced the Marinemaster name to its collection as a series of high-end luxury divers, with immaculate finishing, high spec movements and the performance to match its predominantly Swiss rivals. Though the Marinemaster name isn’t officially used in Seiko’s catalogues anymore, it still hasn’t stopped fans from using this moniker to identify the model which is now the SLA021J1, a very clear and obvious update on the SBDX017 MM300.

The Marinemaster 300 SLA021J1 is a commemorative homage to the first Marinemaster from 1968, Seiko’s reference 6159. It is powered by Seiko’s Caliber 8L35, beating at a stable 28,800VPH (4Hz). The Marinemaster pays proper tribute to the original 1968 hi-beat drive Ref. 6159-7001 and then some. Though not equipped with the high-beat 36,000VPH (5Hz) 8L55 caliber, the 8L35 is still a force to be reckoned with, with a respectably high frequency of 28,800VPH (4Hz).


The 8L35 is essentially an undecorated version of the Grand Seiko's 9S55 caliber, with 26 jewels, 50 hours of power reserve and an accuracy of -10 to +15 seconds per day. It’s a proper demonstration of the company’s impressive watchmaking prowess. Coming with a 44.3mm mono-bloc case (missing the traditional case-back where the movement is installed from the front), it ensures rugged durability and water resistance of up to 300m.

The case has also been hardened with a super-hard (DLC) coating making it more scratch-resistant and wear-resistant. It is certainly tougher than your run-of-the-mill diver. A sapphire crystal with a dual-sided anti-reflective protects the proud blue dial and it features a knurled crown at 4 o'clock (a common and recognizable staple in Seiko's divers).

The bracelet is well executed too, featuring an oyster style design and a folding clasp with a nicely designed slide-lock adjuster for when you need a bit more space to fit it over your wet suit. Or if your wrist needs a bit more space to breathe on a hot day.


The Marinemaster 300 SLA021J1 may be an expensive watch, and its price doesn’t erase the fact that it is ‘still just a Seiko’ but it more than makes up for it. With an immaculate finish (thanks to the mirror like Zaratsu polish on the case), an impeccable movement and of course a level of attention to detail and performance that easily out specs practically anything within its price bracket.

Now, having looked at the very fantastic and expensive MM300, let’s take a look at its little brother, the Baby Marinemaster, and find out what’s what with this rather fetching diver and why it costs over $2000 less than its bigger brother.




The Baby Marinemaster, or the MM200 line as I’ll refer to it from now on, was a series that didn’t really catch on with fans during its initial launch. It’s not a very flawed watch, people just didn’t really like the way the modern hands looked, with the arrow hour hand and sword shaped minute hand. But the design will start to grow on you once you put it on your wrist and you won’t be able to help thinking, ‘Damn, Seiko was right all along’. In fact, this might very well be Seiko’s nicest mid-range diver watch available in the market today.

The MM200 we’ll be looking at in particular will be this one: the Seiko Prospex SPB087J1 in the ever-popular and attractive Pepsi colourway. This special edition release, done in collaboration with Seiko’s long-time partner and diving association PADI, is one of the newer additions to the ever-expanding MM200 line up.

Now right off the bat, the first impressions from this watch are great, as with most of Seiko’s offerings these days. Everything about this watch screams “professional tool watch” from the matte black dial, bright, highly legible luminescent markers and hands, as well as the highly functional Pepsi coloured bezel


Yes, the Pepsi bezel isn’t coloured this way solely to look good—it’s actually functional, with the last (or first if you’re actually using it to time a dive) 45 minutes in blue and the final 15 minutes in red indicating that you should probably get out of the water soon before your oxygen supply runs out.

The round markers and the distinctive indices at 12 o’clock are decidedly more lifted compared to the MM200’s predecessors. The overall case diameter of the SPB083J1 sits at a relatively large 44mm with a 20mm lug width. It’s protected by an anti-reflective scratch-resistant sapphire crystal and its case is treated with Seiko’s Diashield coating, ensuring improved scratch and corrosion resistance. The case is attached to Seiko’s own ridged rubber strap making for a nicely comfortable wear without sacrificing durability.

Power comes from Seiko’s trusty Caliber 6R15 automatic, a step up from the entry level 4r, but below the 8L. And as expected, the movement comes with hacking, hand winding and a modestly beefy 50 hours of power reserve and a respectable 21,600 VPH (3HZ) frequency. The last thing we ought to tell you before we move on from this is that there is a significant difference in thickness between the 2, with the MM300 coming in at 15.4mm and the MM200 coming in at 13.1mm, and that 2.3mm really makes a difference in how the watch feels on the wrist.

It’s no ultra-thin, but then it doesn’t have to be. It really just feels like a normal every day watch, and that’s saying something. With specs and water resistance like it, feeling like a ‘normal’ watch is high praise. But ultimately, as close as they may seem in terms of their names, functions and even appearance, they are vastly different watches.



One was made to be a rugged, no-nonsense performance tool watch with great specs for its price that you can wear every day. The other is an every day luxury tool watch that you can not only pair with your best suit, but with a dive suit as well. Either one you choose though, you can be certain that you’re landing yourself one of the finest watches from Japan.