Marine Hardware: A Practical Guide

Chandlery Guide · Hardware & Metals

Marine hardware failures are rarely sudden. They develop from the wrong material in the wrong environment, or the right material improperly installed, or maintenance deferred until the problem becomes structural. A basic understanding of marine metallurgy and hardware mechanics prevents the majority of avoidable failures — and helps you evaluate what you are actually buying when the chandlery shelves offer five different options for what appears to be the same component.

Stainless Steel Grades: 304 vs. 316

Not all stainless steel is equivalent in a marine environment, and the difference between the two common grades — 304 and 316 — matters significantly for saltwater applications. The primary distinction is molybdenum content: 316 stainless contains 2 to 3 percent molybdenum, which substantially improves resistance to chloride-induced pitting corrosion. In practice, this means that 304 stainless, while technically stainless, will develop rust staining and pitting in direct salt air exposure within a single season. 316 is the correct specification for any deck hardware, rigging hardware, or below-deck fittings exposed to bilge water or spray.

The 316L designation indicates a low-carbon variant of 316 stainless, which is less susceptible to sensitization during welding — a concern for fabricated items where heat is applied. For welded bow rollers, custom chainplates, or any other fabricated stainless work, specifying 316L is the correct approach.

The magnet test that circulates as a way to distinguish 304 from 316 is unreliable. Both grades can be slightly magnetic depending on their manufacturing and working history, and neither is reliably non-magnetic in all conditions. The only way to confirm stainless grade is the material certification from the supplier. For critical hardware purchased from reputable marine chandleries, the grade is specified on the product; for hardware sourced from general industrial suppliers, ask for the certification.

Crevice corrosion is the failure mode that catches many sailors off guard with stainless hardware: even proper 316 stainless will corrode in low-oxygen environments — under a fitting, inside a bolt hole, where water is trapped and cannot circulate. A stainless fitting that looks perfect on the outside can be severely corroded where it contacts the deck. The mitigation is proper bedding compound, annual inspection of fittings under load, and replacement when in doubt.

Bronze: The Underwater Standard

Silicon bronze and naval bronze are the correct materials for underwater fittings: seacocks, through-hull fittings, propeller shaft struts, and traditional block and rigging components on classic designs. Bronze is both resistant to seawater corrosion and compatible with the galvanic environment of a boat's underwater hull — it sits in a favorable position relative to most other underwater metals when the galvanic series is considered.

The critical distinction is between true bronze and naval brass. Naval brass contains a higher zinc content than silicon bronze, which creates a vulnerability to dezincification — a process where seawater selectively leaches zinc from the alloy, leaving behind a weak, porous copper matrix. A dezincified bronze seacock looks intact from the outside but has lost most of its structural integrity. The ABYC (American Boat and Yacht Council) and most classification societies now require silicon bronze or other dezincification-resistant alloys for through-hull fittings. If you are buying replacement seacocks or through-hulls, verify the specification is silicon bronze, not naval brass. The price difference is minor; the consequence difference is not.

On deck, bronze is appropriate for traditional hardware — cleats, blocks, and fairleads on classic wooden boats, and for any application where the aesthetic matters. It does not offer a corrosion advantage over 316 stainless in above-waterline applications, and 316 is now the more common choice for modern production boats.

Aluminum: Masts, Spars, and the Isolation Requirement

Aluminum is used for masts, booms, spinnaker poles, and some deck fittings on production boats primarily because of its weight-to-strength ratio and ease of extrusion into complex sections. The limitation is galvanic incompatibility with stainless steel: aluminum sits significantly lower in the galvanic series than stainless, meaning that wherever dissimilar metals make contact in the presence of an electrolyte (salt water, salt air), the aluminum corrodes preferentially. The stainless fastener that secures an aluminum deck fitting will be the site of active corrosion in the aluminum surrounding it within a few seasons if not properly isolated.

The standard mitigations are TefGel (a PTFE-based anti-corrosion compound) applied to all fastener threads and contact surfaces, and the use of isolating washers or butyl tape between dissimilar metal contact surfaces. Anodized aluminum has a protective oxide layer that improves its corrosion resistance, but the anodizing is destroyed at fastener holes and contact points — where isolation becomes critical. Bare aluminum requires even more diligent protection.

Blocks: Harken, Lewmar, and Ronstan

The three primary block manufacturers used on cruising boats are Harken, Lewmar, and Ronstan, and the quality difference between them for cruising applications is less significant than the marketing suggests. All three produce well-engineered products; the relevant specifications for a given block purchase are the working load limit (WLL) and the breaking load, not the brand name.

Bearing type determines both efficiency and maintenance requirements. Ball-bearing blocks run with less friction and are appropriate for high-cycle applications like mainsheet or spinnaker sheet systems; they require occasional cleaning and light lubrication. Roller-bearing and plain-bearing blocks are adequate for lower-load, lower-cycle applications and require less maintenance. For offshore cruising, where access to spares is limited, the plain-bearing or roller-bearing block in the non-critical position is a reasonable tradeoff for reliability.

Swivel versus fixed blocks: a swivel block allows the block to rotate to align with the load angle, which reduces wear and chafe when the lead angle varies. Use swivel blocks at the head of a tackle where the direction of pull changes; use fixed blocks where the lead is constant. Fiddle blocks — two sheaves in one housing — allow a single block to serve as both the standing part and the hauling part in a purchase, keeping the tackle organized and reducing the number of blocks required.

Winches: Maintenance Is the Product

Lewmar and Harken are the dominant winch manufacturers on production cruising boats, and both produce reliable equipment when properly maintained. The maintenance requirement is annual disassembly, cleaning, inspection, and regreasing — a task that takes about an hour per winch and prevents virtually all of the mechanical failures that winches develop in service.

The components that fail are the pawls (the small spring-loaded ratchet pieces that engage the drum's teeth and prevent backslide), their springs, and the bearings. Pawl springs are inexpensive and should be replaced during every annual service; a broken pawl spring does not cause immediate catastrophic failure but leaves you with a winch that can slip under load. Bearings typically last many years with proper lubrication. The self-tailing jaw — the plastic ring at the top of the drum that grips the line — wears over time and should be inspected annually; replacement jaws are available from both manufacturers and cost far less than discovering the problem mid-tack.

The grease matters: use a waterproof marine grease specified for winch applications, not general-purpose automotive grease. Harken and Lewmar both sell their own specifications; there are several aftermarket alternatives. Do not use oil where grease is specified — oil migrates out of bearings faster and leaves them inadequately lubricated.

Cleats, Cam Cleats, and Horn Cleats

Cam cleats grip line automatically when loaded and release with an upward pull — they are appropriate for applications where quick release is more important than absolute security: traveler control lines, spinnaker halyards in racing applications, and dinghy sheets. They have load limits that should not be exceeded and do not work well with line that is too large or too small in diameter for the cam teeth. Material choices include aluminum (light, standard), nylon (inexpensive, adequate for light loads), and titanium (expensive, weight-sensitive applications).

Horn cleats are the traditional marine cleat — a fixed fitting around which line is wrapped in a figure-eight and locked. They are appropriate for any application requiring reliable, permanent holding: dock lines, anchor lines, mooring lines. For offshore cruising, horn cleats are the correct hardware for anything that needs to stay put when unattended. The load rating of a horn cleat is primarily limited by its mounting — proper through-bolting with backing plates is essential for any cleat under significant load.

Fasteners: The Rule Is Simple

316 stainless for all deck hardware fasteners. Silicon bronze for fasteners going into wood — silicon bronze is compatible with wood preservatives and adhesives, and does not cause the tannin staining that some stainless fasteners produce in teak and mahogany. Never use zinc-plated, cadmium-plated, or unprotected carbon steel fasteners in a marine environment; they will fail within one or two seasons and the resulting corrosion staining is difficult to remove.

Thread sealant choices: TefGel applied to threads prevents galvanic corrosion between dissimilar metals and makes future disassembly possible — use it wherever stainless fasteners enter aluminum fittings or aluminum spars. Loctite 243 (medium-strength thread locker) is appropriate for fasteners that need vibration resistance but must be removable with standard tools. Avoid Loctite 272 (high-strength, red) on anything you may ever need to disassemble without heat — it requires temperatures above 150°C to release, which is impractical in most marine contexts. Butyl tape bedding compound is preferred over polysulfide for deck hardware that may need to be removed in future; polysulfide bonds aggressively and can damage fiberglass when the fitting is eventually pulled.

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Frequently Asked Questions

What is the difference between 316 and 304 stainless steel, and which is correct for marine hardware? 316 stainless contains 2–3% molybdenum, which 304 does not. Molybdenum significantly improves resistance to chloride-induced pitting and crevice corrosion — the dominant failure modes in a saltwater environment. 304 stainless is appropriate for indoor architectural use but corrodes noticeably faster than 316 in marine environments; it is the grade frequently used in budget marine hardware and is identifiable by its slightly different surface finish and, definitively, by magnet testing (316 is less magnetic than 304, though neither is fully non-magnetic). All structural hardware on an offshore boat should be 316 grade minimum.

Why is silicon bronze preferred over naval brass for marine fittings? Naval brass — a copper-zinc-tin alloy — is susceptible to dezincification in seawater over time: the zinc dissolves out of the alloy, leaving a porous, weakened copper matrix that is structurally compromised while appearing intact. Silicon bronze (copper-silicon-manganese, with no zinc) does not dezincify and is the correct alloy for through-hull fittings, seacocks, deck plates, and fasteners in saltwater service. The price premium of silicon bronze over naval brass is modest and fully justified by the safety-critical nature of hull penetrations.

What are the leading block and hardware brands, and how do they differ? Harken, Lewmar, and Ronstan are the three dominant brands for blocks, travellers, and deck hardware. Harken's ball-bearing blocks have the smoothest action under load and are the standard on racing boats and performance cruisers; their line is more expensive but requires less maintenance under continuous use. Lewmar produces solid mid-market hardware with good availability of service parts. Ronstan specialises in low-friction rings and control systems preferred on racing dinghies and performance cruisers where weight and friction minimisation is prioritised. For offshore cruising, any of the three is appropriate; Lewmar's availability advantage for service parts in remote ports is a practical consideration.

How should aluminium-to-stainless contacts be managed to prevent galvanic corrosion? TefGel is the correct isolation compound for aluminium-to-stainless contact points — mast fittings, stainless fasteners through aluminium spars, and stainless hardware bolted to aluminium toerails. Without isolation, the galvanic potential between stainless (noble) and aluminium (active) drives accelerated corrosion of the aluminium, producing the chalky white oxide that indicates active electrolytic corrosion. TefGel is applied to the threads and mating surfaces of each fastener before assembly; it remains effective for several years in immersion service. Lanolin-based compounds and proprietary anti-seize compounds provide partial protection but are inferior to TefGel for long-term aluminium-stainless isolation.

What Loctite grade is correct for marine deck fittings and rigging hardware? Loctite 243 (medium strength, blue) is the correct threadlocking compound for most deck hardware fasteners — it prevents vibration-induced loosening while allowing disassembly with standard tools. Loctite 272 (high strength, red) is for permanent assemblies where disassembly is expected to be rare or never — not appropriate for hardware that requires periodic inspection. Never apply high-strength Loctite to aluminium fasteners or fittings; the chemical action can attack the aluminium. For underwater applications (keel bolts, through-hull fasteners), neither Loctite product is appropriate — these are sealed with marine sealant compounds.

What is the correct bedding compound for deck hardware and through-deck fittings? Butyl tape is the preferred bedding compound for deck hardware that may require future removal — cleats, blocks, stanchion bases, and traveller tracks. Butyl remains pliable indefinitely, seals reliably against water, and allows the fitting to be removed and rebedded without structural damage to the deck laminate. 3M 5200 polyurethane adhesive sealant provides a stronger bond but is extremely difficult to remove and will damage GRP decks on disassembly — it is appropriate for permanent installations where removal is not anticipated. Silicone should not be used as a bedding compound for structural hardware; it does not bond reliably to GRP and becomes a source of deck leaks within 2–3 seasons.