Seiko has expanded the upper end of the Prospex line with two new Marinemaster references developed around the brand’s long relationship with JAMSTEC, the Japan Agency for Marine-Earth Science and Technology. The official announcement was published on March 18, 2026, and the watches are scheduled to reach Seiko Boutiques and selected retailers from July 2026.
The headline piece is the HBF002 JAMSTEC Limited Edition, a 1,000-piece model that turns Arctic research imagery into a blue gradient dial and matching ceramic bezel. Alongside it, Seiko also introduced the black-dial HBF001 as the first regular-production Prospex model powered by the new 8L45 caliber, giving the Marinemaster range a more permanent flagship mechanical diver.
Design and Materials
Seiko says the blue dial texture of the HBF002 is inspired by the route cut through sea ice by an icebreaker, tying the watch directly to JAMSTEC’s Arctic research mission. The HBF001 takes the same 42.6mm Marinemaster platform in a more traditional direction, pairing a black fine-grain dial with a black ceramic bezel for maximum underwater legibility.
Both watches use stainless-steel cases and bracelets with super-hard coating, a dual-curved sapphire crystal, a screw-down crown at 4 o’clock, and 300 meters of water resistance. The exterior still traces the familiar 1968 Seiko diver silhouette, but the case construction and finishing have been updated to position these models above Seiko’s mainstream Prospex releases.
Technical Specifications
Inside both references is the self-winding Caliber 8L45, a 35-jewel mechanical movement beating at 28,800 vibrations per hour. Seiko quotes a 72-hour power reserve and an accuracy range of +10 to -5 seconds per day, positioning the 8L45 as the most precise current mechanical movement in Seiko’s catalog.
The two watches also debut a newly developed clasp with up to 16mm of adjustment in 2mm steps, designed to improve real-world comfort without sacrificing dive-watch robustness. For enthusiasts who found earlier Marinemaster models technically strong but ergonomically stubborn, that may be one of the most meaningful upgrades in day-to-day use.
Horomag’s Take
What makes this release notable is not only the limited-edition story around JAMSTEC, but the fact that Seiko is using the same platform to establish a regular-production Marinemaster with stronger mechanical credentials. HBF002 will likely draw the early attention thanks to its blue dial and 1,000-piece cap, yet HBF001 may prove even more important for collectors who want the new case, clasp, and caliber without chasing a numbered edition.
Sources
Seiko official press release
Seiko Prospex Marinemaster special page
