Seiko offers professional dive watches all over the price spectrum, ranging from around €550 to over six grand. But is the best of them necessarily the most high-end, or can we find the sweet spot somewhere in the middle? Today, we’ll look at the Marinemaster line, from the very first reference to today’s Prospex SLA021J1. Priced at €3,200 / US$3,100, I believe the current model offers Seiko’s most attractive qualities in a very competitive package. Indeed, it may be the only Seiko to rule them all!

I bought my first Seiko watch back in 2014 after I had already been into watches for many years. That’s right; I’d never owned a Seiko before then, other than a random ladies’ model that my roommate once found and donated to me. It has remained untouched in my drawer for over 20 years.

SBDX001 Marinemaster

The Seiko Marinemaster 300 SBDX001

The Seiko Marinemaster

In 2014, I purchased a Seiko “Baby Tuna” SRP231 and a Seiko SKX007. At that point, I realized that I had been missing out on them. I was eyeballing a Marinemaster 300 (SBDX001) but wasn’t ready to spend €2,300 before I had a good idea of the quality of the watch. Then I decided to buy a Seiko Prospex Scuba reference SBDC001 (also known as the “Sumo”) just to have something in the same style as the Marinemaster. If you don’t know, the Prospex collection is Seiko’s line of capable watches for the land, sky, and sea. The name Prospex finds its roots in the words “professional” and “specifications.”

Seiko Marinemaster SBDX001

The Seiko Marinemaster SBDX001

Before spending more money on a Marinemaster or a Grand Seiko, I thought I needed to test the waters. The Sumo left a big impression on me, especially given the retail price of around €600. I saw the Sumo a bit like the “mini” Marinemaster at the time, as back then, the latter had a retail price of €2,300. It was the Marinemaster 300 reference SBDX001 that I was keen on getting.

Seiko Factory Visit Marinemaster case

Zaratsu polishing

In early 2015, I got the Seiko Marinemaster 300 (I wrote a review here), which turned out to be perfect timing as well. A few months later, I received an invitation to visit the Grand Seiko manufactures in Japan. With the Marinemaster 300 strapped on my wrist, I visited several production sites there, including the one in Morioka, where Seiko made the mechanical calibers for the Grand Seiko watches. I was surprised to see that the Marinemaster 300 with its 8L35 caliber was also produced at the same facility where the mechanical Grand Seiko watches came to life. I also learned that the Marinemaster received the same Zaratsu polishing technique.

Seiko MM300 SBDX017 Marinemaster

Seiko MM300 SBDX017

The name Marinemaster disappears

Meanwhile, Seiko replaced the Marinemaster 300 SBDX001 with the SBDX017, giving the model some very slight updates. Later on, that made way for the SLA019J1/SBDX021 (which we compared to Rolex Submariner “Hulk” here). Today, the current model is the Seiko Prospex SLA021J1.

Seiko Prospex MarineMaster 300 SLA021J1

Seiko Prospex SLA021J1

The Marinemaster SBDX001 debuted in 2000 and remained in production for 15 years. In that time, it certainly made its mark as a cult-classic diver. Just to clarify, though Seiko has dropped the Marinemaster name, I will still use it loosely in this article to indicate the later references.

Rolex Submariner Hulk versus Seiko SLA019

The limited-edition SLA019J1 “Marinemaster”

The 8L35 caliber, which is still used in the current variation of the Marinemaster, the SLA021J1, is based on the long-discontinued Grand Seiko 9S55 movement. Now in its 8L35B iteration, it is a great caliber with nice decoration applied.

Seiko Factory Visit

The 8L35(B) caliber, used in the Marinemaster collection, is also made in Morioka.

However, the movement is not the only area where the Marinemaster or SLA021J1 stands out. In comparison to the more affordable models (often with 6R-series movements) models, the finishing of the Marinemaster’s hands and case are also a step above. The polished and brushed finishes are of higher quality and very thoroughly done compared to watches such as the Seiko Prospex SPB077J1. Again, there’s nothing wrong with those watches around the €1,000/$1,000 mark. They are just of a different level of quality than the SLA021J1 and its predecessors.

Seiko Prospex SLA021J1

The Seiko SLA021J1

Today, the Marinemaster 300 equivalent Prospex SLA021J1 has a retail price of €3,200 / US$3,100. This is definitely a step up from most other Prospex dive watches but still a lower price point than many of its (serious) competitors.

Seiko Prospex MarineMaster 300 SLA021J1

With the SLA021J1 or any of its predecessors, you’re buying into an amazing watch based on a vintage 1967 reference 6215 diver from Seiko. In particular, the SBDX017, SLA019J1/SBDX021, and the current SLA021J1 can compete with watches at (much) higher prices. The first Marinemasters, the SBDX001 and SBDX017, both had a Hardlex crystal instead of sapphire. The SBDX017, however, has a later iteration of the caliber 8L35, using MEMS technology for its escapement for higher precision.

With the SBDX017, we also saw Seiko using the Prospex logo on the crown. With the SLA019J1, the Marinemaster name disappeared from the dial (not the smartest move, in my opinion) and made way for the Prospex logo. The SLA019J1 was a green limited edition (of 1,968 pieces), and the current SLA021J1 is the standard version in the Seiko catalog.

Seiko Prospex MarineMaster 300 SLA021J1

Hard-coated stainless steel

The SLA021J1 also utilizes a ceramic bezel insert and a super-hard-coated stainless steel case. Seiko has applied this DiaShield coating since the SBDX017 and made the switch to a ceramic bezel insert with the SLA019J1. Scratching the surfaces of these watches should not be easy. At nearly 220 grams with all links in the bracelet, the Marinemaster certainly isn’t lightweight. That said, the weight does suit the watch’s proportions. With a diameter of 44.3mm, a thickness of 15.4mm, and a lug-to-lug measurement of 50.5mm, it is not for everyone.

The SLA021J1 on the wrist

Whether you go for a brand-new Seiko SLA021J1 or choose a pre-owned SBDX001 or SBDX017, they all come with a monobloc case. This ensures it doesn’t need a helium valve to keep the watch in one piece during decompression after a saturation dive. Fun fact: because resale value is so important for many watch buyers these days, the prices of these Marinemasters (and successors) stay very stable. Even 10-year-old SBDX001 Marinemaster 300 models go for more than what they retailed for.

Seiko Prospex LX SNR029J1

Prospex LX SNR029J1

Other Prospex watches

Although Seiko made a big impression with the Prospex LX series, the price point of €6,100 / $6,000 for the titanium SNR029J1 comes awfully close to that of a Grand Seiko Diver (SBGA229). The Seiko Marinemasters, all the way up to the current SLA021J1 reference, offer a watch with the same kind of exceptional finishing on the case and a well-respected 8L35 movement for approximately half the price of a Prospex LX. Compared to the lower-priced Seiko Prospex watches, the SLA021J1 is just steps above in terms of the finishing and the movement inside. This means that the SLA021J1 is an incredible offer, not only in comparison to professional dive watches from other brands but also to its competition from Seiko.

Nicknames and reference numbers took over

There are a lot of reference numbers in this article. My apologies for that. Unfortunately, Seiko either uses references or nicknames for its watches these days. The Marinemaster 300 lost its name with the introduction of the green edition, which just went by its reference SLA019J1 and “Prospex” due to having the Prospex logo on the dial. The Seiko Prospex SLA021J1 is a piece of art, and if it weren’t for my SBDX001 from 2015, I would gladly buy the SLA021J1. It’s a serious watch for some serious water business, but it can also be worn casually by anyone who loves a good dive watch.

I do love a lot of the Seiko Prospex watches that I see coming into our offices, such as the popular SPB143J1. However, once you have the Marinemaster 300 or one of its Prospex successors, there’s no looking back. This do-it-all Seiko is certainly not as attractively priced as some of the other Prospex models, but it shares some of the same characteristics and values as its more expensive Grand Seiko relatives.

What are your thoughts on the Seiko Marinemaster family? Do let us know in the comments below.