Forespar Seacocks

Why Forespar Seacocks Stand Apart from the Competition

When it comes to protecting your hull below the waterline, few components are more critical — or more often overlooked — than the seacock. Forespar, a California-based marine innovator building products since 1966, has made its mark in the seacocks category through one defining innovation: Marelon®, a proprietary glass-reinforced polymer composite that delivers what traditional bronze simply cannot — complete immunity to corrosion and electrolysis.

Marelon® Technology: The Core of Forespar Seacocks

Forespar's seacocks are built around their exclusive Marelon® material, a carefully engineered formulation of polymer composite compounds. Unlike bronze or brass fittings that are vulnerable to galvanic corrosion — especially in saltwater environments or on boats with mixed-metal systems — Marelon seacocks will never corrode, pit, or seize. The material is also UV-stabilized, meaning it resists brittleness and degradation from sun exposure over years of service.

Every Forespar Marelon seacock exceeds ABYC H-27 standards and carries UL approval for use both above and below the waterline. Forespar's threaded connections use NPSM (National Standard Free-Fitting Straight Mechanical Pipe Thread) — the standard for most U.S. marine plumbing — ensuring proper, leak-free sealing when used with Teflon tape or common marine thread sealants.

Product Lines: From Flanged Seacocks to Full-Flow Systems

Forespar offers several distinct seacock configurations to suit different installation needs:

• Flange Mounting Seacocks (MF 849 Series): Available in sizes from 1/2" to 2", these are designed as direct replacements for in-line bronze valves. They feature a traditional 3-bolt flange mount and are compatible with a variety of attachments.
• Full-Flow Seacocks with Mushroom Thru-Hull: An integrated 2-part system pairing a Marelon® valve with a precisely matched mushroom-head thru-hull. The thru-hull uses a proprietary "buttress" style thread with flat thread faces, providing superior strength for below-waterline installations. This package is specifically engineered to eliminate the thread mismatch problems that arise when mixing parts from different manufacturers.
• Pro Series Seacocks: Designed to meet the demanding requirements of professional boatbuilders and serious cruisers, the Pro Series features three-part construction for long-term maintainability. Each valve can be fully disassembled for cleaning and O-ring replacement without hauling the boat. Pro Series seacocks are available in screened, flush, and anti-venturi thru-hull styles, and include a bung plug stored directly in the handle for emergency use.

Safety, Compliance, and Maintainability

One thoughtful detail that sets Forespar seacocks apart is the integrated emergency bung plug stored in the valve handle itself, allowing the owner to quickly plug the thru-hull for maintenance without dry-docking the vessel. The three-part construction of the Pro Series makes routine O-ring replacement straightforward — a maintenance task that is necessary on every seacock regardless of material, but far easier to accomplish on a Forespar fitting.

Forespar's "93" series of valves and thru-hull fittings also meets all design criteria and exceeds mechanical property requirements specified by ISO 150/188 for small craft seacocks and thru-hull fittings (non-metallic), making them suitable for international racing and cruising applications alike.

Whether you are re-fitting an aging coastal cruiser or specifying fittings for a new build, Forespar's Marelon seacocks offer a proven, low-maintenance alternative to traditional metal fittings. Explore the full seacocks category or learn more about the complete range of marine plumbing and hardware on the Forespar brand page.