Aluminum hull boats are a popular choice for commercial operators, fishing vessels, and recreational boats alike — lightweight, durable, and resistant to saltwater corrosion when properly maintained. But aluminum has a vulnerability that surprises many boat owners: galvanic corrosion when mated with the wrong fasteners.
Choosing the wrong marine hardware on an aluminum hull isn't just a performance issue — it can lead to fastener failure, structural damage, and costly repairs. In this guide, we break down what aluminum boat owners and builders need to know before selecting deck hardware, cleats, turn buttons, and fasteners.
Understanding Galvanic Corrosion on Aluminum Boats
Galvanic corrosion (also called bimetallic corrosion) occurs when two dissimilar metals are electrically connected in the presence of an electrolyte — in marine environments, that's saltwater. When this happens, the more active (less noble) metal corrodes faster than it would alone, while the more noble metal is protected.
Aluminum is a moderately active metal. In the galvanic series, it sits well below stainless steel, copper, and nickel. This means when aluminum is paired with these metals in a marine environment, the aluminum will preferentially corrode — even if the other metal looks perfectly fine.
⚡ The Galvanic Series: Why It Matters
In seawater, metals are ranked by their electrochemical potential. The further apart two metals are in the series, the more aggressive the galvanic corrosion on the more active (anodic) metal. Aluminum is anodic relative to SS316, copper, and most marine bronzes — meaning it will corrode preferentially when paired with them without proper isolation.
Fastener Material Options for Aluminum Hulls
SS316 Stainless Steel — Best All-Round Choice
SS316 (AISI 316) is the most widely recommended stainless steel grade for marine environments. Its key advantage over SS304 is the addition of 2–3% molybdenum, which significantly improves resistance to pitting and crevice corrosion in chloride-rich seawater.
When used on aluminum hulls, SS316 is considered acceptable with proper isolation — typically by using a nylon or rubber isolation washer between the fastener and the aluminum surface. This prevents direct metal-to-metal contact and breaks the electrical circuit that drives galvanic corrosion.
SNOWL's 4000BS316 turn button uses SS316 stainless steel as its primary material, making it a suitable deck hardware option for aluminum hull boats when installed with proper isolation washers. The SS316 body provides excellent corrosion resistance, while the mounting configuration allows for a barrier layer between the fastener and the aluminum substrate.
Silicon Bronze — Excellent but Expensive
Silicon bronze is one of the most compatible metals for aluminum. It sits close to aluminum in the galvanic series, producing minimal galvanic corrosion even in direct contact. For below-deck applications or structural connections, silicon bronze fasteners are an excellent choice.
The downside: silicon bronze is significantly more expensive than SS316 and is primarily used for through-hull fittings and below-waterline hardware rather than deck accessories.
Aluminum Rivets and Fasteners
Aluminum rivets are commonly used for hull assembly and are obviously the most galvanically compatible option. However, they lack the strength and longevity of SS316 for deck hardware applications where repeated removal is required.
Avoid These on Aluminum Hulls
- Standard steel or zinc-plated fasteners — Rapidly corrode in saltwater and accelerate corrosion on aluminum through galvanic coupling.
- Uncoated copper-based fasteners — While copper itself resists corrosion, it creates strong galvanic coupling with aluminum. Use only with rubber washers and only in low-risk locations.
- 304 Stainless Steel in critical applications — SS304 lacks the molybdenum content of SS316 and is more prone to pitting and crevice corrosion in saltwater. For any hardware below the waterline or in high-splash zones, SS316 is the minimum acceptable grade.
Installation Best Practices for Aluminum Hull Fasteners
Material selection is only part of the equation. Installation practice matters equally:
Use Isolation Washers
Always use nylon, PTFE (Teflon), or EPDM rubber washers between any metal fastener and the aluminum hull surface. These create a dielectric barrier that prevents electron flow between the two metals. Replace washers during any hardware re-installation — old, compressed washers may no longer provide adequate isolation.
Apply Marine Sealant
Sealant around the fastener shaft serves two purposes: it prevents water ingress into the mounting hole (which can cause corrosion inside the hull) and adds another layer of electrical isolation. Butyl tape or marine-grade polysulfide sealant are preferred over silicone in aluminum applications.
Monitor High-Risk Locations
Hardware installed in areas prone to water entrapment — low points on the deck, areas around scuppers, or any location where water can pool — faces the highest galvanic corrosion risk. Inspect these locations regularly, especially after storm events or heavy use.
Keep Dissimilar Metals Separated
If you must use multiple fastener types on the same vessel, group like materials together. Don't use SS316 fasteners for one piece of hardware and copper-based fasteners for another nearby item — the electrical potential difference can still create localized corrosion issues in the electrolyte film on the hull surface.
🔧 Quick Checklist: Fastener Selection for Aluminum Hulls
- ✅ SS316 is the minimum acceptable stainless steel grade for marine deck hardware
- ✅ Always use isolation washers (nylon, EPDM, or PTFE) between fastener and aluminum
- ✅ Apply marine sealant around all through-deck fasteners
- ✅ Inspect high-splash and water-trap areas after heavy use
- ✅ Never reuse compressed or deteriorated isolation washers
- ✅ Keep dissimilar metals (SS304 vs SS316 vs copper) from sharing electrical contact
Why SNOWL Uses SS316 for Marine Applications
SNOWL has manufactured marine hardware since 1995. All SS316 products — including turn buttons, snap fasteners, and OWOZ quick-release deck hardware — are produced in grades confirmed by material composition certificates.
SS316's 2–3% molybdenum content is what separates it from commodity SS304 in marine service. That molybdenum dramatically increases pitting resistance equivalent number (PREN), making it the material of choice for any hardware exposed to salt spray or tidal wetting. For aluminum hull applications specifically, SS316 with proper isolation is the practical, cost-effective choice that balances galvanic compatibility with long-term durability.
Need Help Selecting the Right Fastener for Your Aluminum Hull?
SNOWL provides material certificates and corrosion resistance documentation for all marine-grade products. Contact us to discuss fastener selection for your specific aluminum boat application.
Get in Touch →Article published May 2026. Galvanic corrosion principles reference ASTM G82 and ISO 9227. SNOWL is a marine fastener manufacturer based in Hong Kong, established 1995. Product material specifications are available on request.