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Mass-produced#1 in family

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Top-tier supplier movement · caliber Alpina Cal. AL-525: ETA 2892-A2 base, Alpina-finished, 28,800bph, 38h PR, 21j; used in Alpiner 4 and Seastrong Diver; Alpina sport watch workhorse · 38h power reserve
Medium-large: suits wrists 6.5 in+ (16.5 cm+)
42 mm case. Wears confidently on average to larger wrists. May overhang on slender builds.

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Authentication

The Seastrong bezel must rotate counterclockwise only; both-direction rotation means the ratchet has failed and the 300m rating cannot be trusted.

Known issues in the market
  • Bezel ratchet wear allowing bidirectional rotation is a safety concern on a dive watch; this is a service-required condition, not a cosmetic issue.
AreaWhat to checkWhat is correctRed flag
caseUnidirectional rotating bezelBezel rotates counterclockwise only; positive ratchet click at each index positionBezel rotates clockwise as well as counterclockwise; worn or failed ratchet mechanism
dial"Seastrong" name on dial"Seastrong" name present on dialMissing "Seastrong" text; wrong reference or non-genuine dial
movementETA 2892-A2 movement architectureETA 2892-A2 movement layout visible through casebackNon-ETA-2892 movement architecture; non-genuine movement swap
Common legitimate replacements
  • Bezel insert; Alpina OEM insert for 300m rating.
  • Crystal; sapphire standard.
Expert resources: Alpina authorized service; Alpina Seastrong product documentation.

Authentication guide

Last reviewed June 2026

The Seastrong Diver 300 is Alpina's dive specification watch using the AL-525 movement in a 300m-rated case. Caseback diver certification text is the primary document to verify.

Known reproduction risks

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LOW

Not a counterfeit target.

  • Replicas typically have a bidirectional bezel regardless of markings
  • Lume on hour markers is thin on replicas; genuine Seastrong has chunky, deeply filled markers

Dial variants by era

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EraDescriptionIdentifiers
2015 to present44mm steel case. Rotating unidirectional bezel with 60-minute aluminium or ceramic insert. Bold applied markers with heavy lume. Date at 3. Red alpine triangle at 12.
  • Bezel rotates counterclockwise only (safety requirement for dive spec)
  • Bezel pip at 12 should be lumed and clearly defined
  • Applied markers are substantial and flat-topped; thin or pointed markers are wrong

Service part flags

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Crown

Original: Screw-down crown with Alpina logo; sized slightly larger than dress variants for wet-hand operation.

Replacement tells
  • Crown that does not achieve full thread engagement means the tube is damaged or the crown is mismatched
  • After full tightening, the crown should sit flush with the case side; proud or recessed crown indicates wrong part
Bezel Insert

Original: Aluminium or ceramic insert with 60-minute scale and lumed pip.

Replacement tells
  • Bidirectional bezel after service is an incorrect replacement mechanism
  • Insert colour mismatch to the original specification (e.g., blue insert on a black-dial reference) indicates aftermarket

Case back markings

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2015 to present
  • "ALPINA GENEVE SEASTRONG DIVER 300"
  • "AL-525" movement caliber
  • "Swiss Made", "Water Resistant 300M / 1000ft"
  • ISO 6425 diver certification statement may appear on caseback or be implied by the 300M rating
  • Serial and reference numbers

Movement tells

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  • AL-525 is standard across the Seastrong line; same service notes as Alpiner 4.
  • After pressure testing to 300M specification, the crown tube and caseback seal must be replaced; a watch serviced without new seals will not meet spec.
  • Hack seconds is present; confirm the second hand stops cleanly when crown is pulled.
Sources: Alpina Seastrong Diver 300 product page.

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