More enjoyment of your ship, more comfort and safer sailing.
Aluminum and stainless steel
Many sailing yachts have both aluminum and stainless steel components. On a sailing yacht, you should always insulate aluminum from stainless steel (AISI/SS). Without insulation, galvanic corrosion will occur—and that is something you always want to avoid. Aluminum and stainless steel are far apart in the galvanic series; without insulation, aluminum will corrode rapidly, especially in a saltwater environment.
Below is more information about the effects of galvanic corrosion and how proper insulation prevents it.
Consequences of galvanic corrosion
The consequences of galvanic corrosion between aluminum and stainless steel (SS) can be severe, especially on a sailing yacht where saltwater accelerates the process. Since aluminum is the “less noble” metal, it will always be the sacrificial material when in electrical conductive contact with stainless steel under moist or salty conditions. Here are the main effects:
🔥 1. Rapid degradation of aluminum
Aluminum can appear to be “eaten away.” Common signs include:
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Powdery white oxidation (aluminum oxide)
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Pitting: small craters in the metal
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Flaking edges or screw holes
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Weakening of deck fittings, mast profiles, or booms
⚓ 2. Weakened structure → potential danger
Ongoing corrosion can lead to:
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Cracks in aluminum
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Loosening of fittings
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Mast fittings tearing away
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Deck or hull penetrations losing load-bearing capacity
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Rigging attachment points failing
On a sailing yacht, this can result in structural damage.
🌊 3. Seizing / ‘cold welding’ of stainless steel to aluminum
Corrosion products and stress can cause aluminum to “stick” to stainless steel. This can result in:
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Screws that cannot be removed
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Damage to aluminum when attempting to unscrew
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Stainless bolts breaking due to being frozen in corrosion
⚠️ 4. Water leaks
Corrosion around holes and bolts causes aluminum to expand (oxidation), which can lead to:
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Micro-cracks
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Degradation of sealant
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Leaks around fittings, windows, and deck penetrations
⚓ 5. Loss of electrical insulation / current leakage
As corrosion progresses, electrical resistance can change. This can:
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Accelerate electrolytic corrosion
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Cause failures in grounding or lightning protection systems
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Affect ICs and equipment if corrosion spreads to electrical systems
🔍 Practical signs (commonly observed on yachts)
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White powder deposits around stainless steel bolts in an aluminum mast
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Corrosion spots under stainless fittings
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Seized boom or mast fittings
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Pitting in aluminum deck plates under stainless railing bases
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“Blisters” under coatings on aluminum parts (coating lifting)
Good insulation prevents galvanic corrosion
You can prevent all the negative effects of contact between aluminum and stainless steel with proper insulation.
Here are the most commonly used and effective solutions onboard:
✔️ 1. Duralac
A classic, widely used anti-corrosion paste.
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Provides long-lasting protection against galvanic corrosion
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Ideal for bolt and screw connections
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Hardens but remains effective
✔️ 2. Tef-Gel
A modern alternative to Duralac — even more popular.
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Does not harden; remains spreadable
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Excellent protection against corrosion and seizing
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Ideal for mast fittings, blocks, and hardware
✔️ 3. Plastic or nylon washers / bushings
Mechanical insulation.
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Placed between bolt head/nut and aluminum surface
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Optionally, a plastic bushing in the bolt hole
✔️ 4. Mylar, plastic, or rubber shims
Used for larger contact areas (e.g., a stainless bracket on an aluminum mast)
✔️ 5. Teflon tape (PTFE tape)
Can provide temporary help on screw connections but is less durable than Duralac or Tef-Gel
Practical tip
Always use:
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A plastic washer/bushing for physical separation
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Duralac or Tef-Gel on the threads
This combination provides the best and longest-lasting protection.
