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Hands-On: Seiko Marinemaster SLA023
Going Deep With The Blue Marinemaster

With its history going back to the 1965, Seiko has been making dive watches for quite some time now.  We recently touched on the trilogy of Seiko dive watches celebrating 55 years. In the early 2000s, Seiko introduced the SBDX001 MarineMaster which became a cult classic with the case design that resembles the 6215-7000 from 1967 but with a modern Grand Seiko automatic movement powering inside the monobloc case. In 2015, the watch received some upgrades and was renamed SBDX017 with the new MEMS technology and Diashield treatment to the case for better protection against scratches. All this leads to the SLA023, which was introduced in Baselworld 2019, but somehow didn’t receive much media coverage. 

When I found out about this watch, the deep blue dial immediately grabbed my attention. After researching online to see Seiko has updated the bezel to ceramic and also updated the crystal from Hardlex to sapphire, it was on my short list of watches I had to get my hands on. With that in mind, my luck came in March 2020 and now, let’s take a deep dive into this review.

After many updates and 20 years of production, the case remains the same size with a diameter of 44.3, however when worn on the wrist, the short lugs makes this wear much like a 42mm watch. In addition, when seen from the caseback, the design of the monobloc case is curved so the actual area that sits on the wrist is only 35mm as seen from this photo. 

This unique design trick allows the watch to be worn comfortably despite it’s actual size! Compared with a traditional watch case, where the crystal is inserted to the case and then sealed and a caseback that is screwed in, the monobloc case only has one entrance from the crystal side. This reduces the chances of water intrusion as there is no caseback since the case is built in one piece.

Even though there are no actual changes from previous generations, the case is still a marvel to look at with the zaratsu polishingZaratsu Polishing Zaratsu polishing is a type of polishing technique used in watchmaking, specifically for the polishing of steel components, such as the case, lugs, and bracelet. It is a process that uses a spinning circular disk with an abrasive surface. The craftsperson, holding the watch part, applies a certain level of pressure and uses a specific angle to ultimately achieve a mirror-like finish. [Learn More] on the side case and curvature and nice brushed edge on both sides of the mid case and the top of the lugs. There is no doubt the level of craftsmanship that was brought into this case design and build. With the Diashield treatment received, it should protect the case against scratches so the zaratsu polishing should last quite a while. It is too short of a time frame for me to say how will this hold up but so far, there has been no visible scratches at the time of writing despite wearing this daily for the past 7 weeks.

Sitting at the top of the case is the much talked about bezel with ceramic insert. It still has the indented markers and now a lumed triangle instead of a pip at 12. The first 20 minutes are lumed as well with 5 minute increments. The bezel is 120 clicks and unidirectional with coined edges.

The crownCrown The knob on the outside of the watch that you typically use to either wind the mainspring or set the time [Learn More] is still at 4 o’clock as before, so the crown does not dig into the wrist. As is with the new generation of Prospex watches, the crown is now signed with the Prospex logo “X” as seen on the previous profile picture.

The blue dial is what drew my attention at first and after playing around with this for a bit, I realized the blue has a bit of range as it shifts from navy blue to a bright sunburst blue directly under the sun. Gone are the “Marinemaster” texts but instead replaced with the Prospex logo “X” This has been coming as Seiko has been updating its line up of professional series into the Prospex line in recent years. The SLA023 is a professional dive watch and therefore falls into the Prospex category. The text “300m” is now marked in yellow on the blue dial and this matches the gold accent seconds hand nicely.

The indexes are applied and filled with the Seiko proprietary Lumibrite. This is definitely stronger than any dive watch I have owned and even brighter than the SKX and has longer duration as well. The hand sets are finely brushed and everything received its share of Lumibrite as seen in the photos.

Beating inside is the 8L35B, which is the same movement as the SBDX017 with the MEMS technology. It is an undecorated version of the Grand Seiko 9S55 with less movement decoration and no regulation. So while the 9S55 has higher accuracy, the listed accuracy for the 8L35B is +15/-10 seconds a day. 

During the brief period I have owned the watch it has been consistently about 3.8 seconds fast a day, definitely within COSC specs. As previously mentioned MEMS helps the watch maintain isochronism so when the watch is low in power, the accuracy does not become erratic. The movement also has the magic level system common in Seiko/Grand Seiko watches, which increases the efficiency of the rotor, so even sitting in front of a desk all day wearing the watch, it will easily charge to full power with no issue. This is needed as the power reserveRéserve de marche Also known as Power Reserve. A watch's power reserve refers to the amount of time a mechanical watch can run without being wound. The power reserve of a mechanical watch can vary depending on the size of the mainspring, the efficiency of the gear train, and the rate at which the mainspring releases energy. If a watch has a Power Reserve 'complication' it simply means that the status of the power reserve can be seen on the watch itself (either on the dial or movement side of the watch). [Learn More] on the 8L35B is 50 hours, while it is still a full 2 days, it is a big lagging when many movements these days run for 3 days/72 hours easily.

Being a professional divers watch, the watch comes with a bracelet. After sizing the bracelet, it wears well on my wrist, especially with the divers extension, allowing the watch to expand during hot summer days after a few beers. 

While this is a great function, I do wish Seiko put a bit more thought into the bracelet as this extension is stamped and feels cheap. In addition, the clasp and 3 link bracelet could use an update that was received in the LX line up. However, it opens up the option for leather straps and this watch definitely works great on other styles of straps.

Although this is a big watch (see photo comparison with the Big Pilot) the watch wears very well as the short lug to lug makes this wear smaller than the 44mm case size suggests. The matching ceramic bezel with the blue dial is great and I get lost looking at it.   

Sure, I definitely think Seiko could trim another 2mm off the case diameter and height, but on the wrist, it isn’t an issue.  I have thoroughly enjoyed every second of this watch on my wrist and I look forward to having this with me for many years to come.  

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  1. Great write-up Jeff! Aways enjoy your hands-on real talk. Such a great watch and sensible alternative to the great (and expensive) LX. Also, how big is the BP if it dwarfs the MM? 😅👍

  2. Great timing for this article. I’ve got a SLA023 en route to me from Japan as we speak. I’ve ordered the CrafterBlue fitted rubber strap that works with the MM300 OEM adjustable strap. I went with brown rubber as I feel that plays with the blue of the dial nicely. This will be my first ever Marine Master and I am extremely excited. Cannot wait for it to arrive. Great write-up.

    1. Let me know how you like it on the crafter blue, I was tempted to go for the orange but ended up with the Uncle Seiko orange strap for now, I wish they had a blue strap for the SLA023!

      1. I’ll absolutely report back on the CrafterBlue once the strap (and the watch for that matter) arrive. I was disappointed that they don’t offer a fitted Blue strap for the SLA023. Maybe if we bug them enough, they’ll make it happen. For now, I’m really hoping the brown rubber will work with the blue dial and bezel. If you want, you can keep an eye on my instagram as I tend to post all of my watch’s there (probably far too often). I’ve always really been interested in the MM300, but never enough to actually make the purchase happen. This colorway of the 023 had me from the moment I saw it. My Grand Seiko “Whirlpool” SBGH267 also uses a blue dial and gold second hand, so naturally if I was going to add a MM300 along side it, it had to be the 023.

        My instagram username is @canuckrs

    2. Congrats with the new watch incoming! I’m confident the brown strap will work very well with the blue dial. Brown strap and blue dial rarely fails to impress 🙂

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