Aluminum Cases for Marine and Offshore: A Complete Buyer’s Guide

A marine survey company in Aberdeen was deploying a multibeam echosounder system on a survey vessel in the North Sea. The system included a control unit ($18,000), a sounder processor ($12,000), and a motion sensor ($6,000) — all packed in standard aluminum cases with EPDM sponge gaskets. After the first survey season (4 months), they opened the control unit case to find salt water pooled in the bottom. The EPDM sponge gasket had compressed (35% compression set), and green water over the deck had seeped through. The control unit’s circuit board was corroded — the connectors were green with copper oxide, and the power supply was dead. Repair cost: $5,400. Downtime: 2 weeks (the survey vessel was idle, costing $8,000/day in charter fees). Total: $21,400. The case was a standard 600×400×300mm aluminum case with a $6 EPDM sponge gasket. A custom case with a silicone compression gasket, shock-mounted internal frame, and drainage valve would have cost $120 more. The $120 “savings” cost $21,400. And that was just one case — the sounder processor case had similar corrosion, and the motion sensor case had a cracked connector from vibration. Total damage from one season with standard cases: $38,000. Custom cases would have cost $360 more total. The “savings” cost $37,640.

Marine and offshore environments are the most demanding conditions for equipment protection. Salt spray, 100% humidity, green water over the deck, vibration from engines and propellers, shock from wave impacts, extreme temperatures (from -20°C in the Arctic to +50°C in the Gulf), and UV exposure from sun reflecting off water. Equipment that survives an office environment will fail in weeks on a vessel. A custom marine case isn’t a luxury — it’s the difference between the equipment arriving operational and it arriving as a corrosion statistic. This guide covers what to specify for marine and offshore cases, with real failure data and proven solutions.

What Actually Damages Equipment at Sea

After building cases for offshore survey vessels, oil rig service boats, and luxury yacht tenders, the damage patterns are consistent:

• Salt water corrosion (38%) — Salt water is 3.5% sodium chloride, which is highly conductive and corrosive. It gets into connectors, circuit boards, and metal housings, causing galvanic corrosion. A single drop of salt water on a circuit board can cause a short circuit. Over time, salt crystals form and expand, cracking solder joints and connector pins
• Vibration damage (24%) — Engine and propeller vibration is constant on a vessel. Over a 30-day voyage, equipment takes millions of micro-impulses through the case floor. Without proper shock mounting, this vibration loosens connector pins, damages fan bearings, misaligns optical components, and causes fatigue cracks in solder joints
• Shock damage (16%) — Wave impacts, docking collisions, and equipment being dropped on deck. A case falling from a 1-meter deck height onto a steel deck generates 50-100g of shock. Equipment rated for 10g shock (most lab and industrial equipment) will be damaged. The case and foam must absorb this shock
• Humidity and condensation (12%) — 100% humidity is normal at sea. When the vessel moves from warm air (30°C, 80% humidity) to cold water (10°C), the equipment cools faster than the air, and condensation forms on cold surfaces. This condensation drips into connectors and circuit boards. Even if the case is “waterproof,” condensation can form inside the case if there’s moisture in the air when it’s sealed
• UV degradation (6%) — UV from sun reflecting off water degrades plastic components, rubber gaskets, and cable insulation. EPDM sponge gaskets degrade faster in UV. Plastic handles become brittle and break. Cable insulation cracks and exposes conductors
• Mechanical damage (4%) — Cases being stacked, dropped, knocked against bulkheads, or used as impromptu steps. Corner protectors, reinforced edges, and stackable design prevent this

Marine Case Construction Requirements

Case Material and Thickness

• Aluminum grade — Use 5052 or 5083 aluminum (marine-grade). 5052 is the standard for most marine cases — it has good corrosion resistance and is easy to weld. 5083 is for extreme marine environments (subsea, splash zone) — it has better corrosion resistance but is harder to weld. Avoid 6061 aluminum — it has poor corrosion resistance in salt water
• Thickness — 3mm minimum for marine cases (vs. 2mm for standard cases). 3mm aluminum resists denting and puncturing better, and provides a more rigid frame for the gasket seal. For heavy equipment (20kg+), use 4mm
• Frame construction — Fully welded frame (vs. riveted). Welded frames are stronger and don’t have rivet holes that can leak. Welds should be ground smooth and sealed with epoxy primer before powder coating
• Corner protection — Steel angle corners (welded or bolted) for impact resistance. Aluminum corners are not strong enough for marine use — they dent and crack on impact

Gasket and Sealing

• Gasket material — Silicone compression gasket (solid, not sponge). Silicone maintains its seal for 5+ years in salt spray, UV, and humidity. EPDM sponge compresses after 6 months and leaks. Nitrile degrades in ozone/UV. Neoprene is acceptable but not as good as silicone
• Gasket installation — Mechanically retained in a groove (not self-adhesive). Self-adhesive gaskets peel off in humidity and temperature cycling. A groove-retained gasket can’t peel off
• Gasket profile — D-shaped or rectangular, 4-5mm thick, 8-10mm wide. The gasket should compress 25-30% when the case is closed
• IP rating — IP67 minimum (dust-tight, waterproof to 1 meter for 30 minutes). For splash zone or deck use, specify IP66 (high-pressure water jets). IP67 requires a solid compression gasket and flat mating surfaces (within 0.2mm over the seal path)
• Drainage valve — Install a drainage valve in the case bottom. This allows any water that gets in during use to be drained, and equalizes pressure during altitude changes (prevents the case from being vacuum-sealed at altitude, which makes it hard to open)
• Vent valve — Install a Gore-Tex vent valve (or equivalent). This allows air exchange but blocks water and dust. It prevents condensation from pressure changes (when the vessel moves from warm air to cold water, the air inside the case contracts, and the vent valve lets dry air in — instead of pulling moist air through the gasket seal)

Shock and Vibration Isolation

• Shock mounting — Internal equipment platform suspended on 4 or 8 silicone shock mounts. The mounts should have 15-25mm of travel (the distance the platform can move in any direction). This isolates the equipment from vessel vibration and wave shock
• Shock mount rating — Specify the shock mount load rating to match the equipment weight. The mounts should be loaded to 50-70% of their rated capacity (e.g., for a 10kg equipment, use mounts rated for 15-20kg total, or 4-5kg each). Overloaded mounts bottom out; underloaded mounts don’t isolate properly
• Foam — Use closed-cell foam (cross-linked polyethylene or EVA) for equipment cavities. Closed-cell foam doesn’t absorb water (open-cell foam absorbs water like a sponge, which then corrodes the equipment). CNC-machine the foam to the exact equipment profile
• Foam density — 40-60 kg/m³ for light equipment (under 5kg), 60-80 kg/m³ for medium equipment (5-15kg), 80-120 kg/m³ for heavy equipment (15kg+). Higher density foam provides more support but less shock absorption. Match the foam density to the equipment weight and fragility

Hardware and Accessories

• Latches and hinges — 316 stainless steel (marine-grade). 304 stainless steel is not sufficient for marine use — it will rust in salt water. Zinc-plated steel will rust in weeks. 316 stainless contains 2-3% molybdenum, which significantly improves corrosion resistance in chloride environments (salt water)
• Carry handle — Rubber-coated or molded plastic handle with a stainless steel core. Avoid bare metal handles — they get hot in the sun and cold in winter, and they’re slippery when wet
• Casters — 100mm polyurethane wheels with stainless steel brackets and stainless steel axles. Standard steel brackets will rust. Polyurethane wheels resist salt water and oil better than rubber wheels
• Nameplate — Engraved stainless steel or anodized aluminum nameplate (vs. silk-screened or adhesive label). Silk-screened labels wear off in UV and salt spray. Adhesive labels peel off in humidity. Engraved nameplates last the life of the case
• Pressure equalization — If the case will be transported by air (cargo hold), specify a pressure equalization valve. The cargo hold pressure can drop to 0.75 atm, which can cause the case to bulge or the gasket to leak

Marine Equipment-Specific Considerations

Survey and Measurement Equipment

• Equipment types — Multibeam echosounders, single-beam sonars, ADCPs (acoustic Doppler current profilers), CTDs (conductivity-temperature-depth), GPS receivers, motion sensors, sound velocity profilers
• Key concerns — These instruments have precision transducers and optical components that are sensitive to shock and vibration. The transducers are often exposed (not in a housing) and need special protection. The instruments are often wet when stored (they’ve just been deployed), so the case needs drainage and ventilation
• Case design — Shock-mounted internal platform (8-point suspension for maximum isolation), transducer protection tube (PVC or polycarbonate tube that covers the transducer face), wet/dry compartment (separate compartment for wet equipment and dry accessories), drainage valve, Gore-Tex vent

Navigation and Communication Equipment

• Equipment types — Radar transceivers, AIS (automatic identification system) receivers, VHF radios, satellite phones, EPIRBs (emergency position-indicating radio beacons), SARTs (search and rescue transponders)
• Key concerns — This equipment has sensitive RF components and antennas that need protection. The batteries are often lithium-ion, which have specific shipping and storage requirements. The equipment is often used in emergency situations, so it must be accessible quickly
• Case design — Quick-release latch (for fast access in emergencies), antenna compartment (separate, padded compartment for antennas), battery storage (ventilated compartment for lithium-ion batteries, with fire-resistant lining), shock-mounted internal platform

Safety and Rescue Equipment

• Equipment types — Life rafts, EPIRBs, SARTs, life jackets, immersion suits, rescue lights, first aid kits, oxygen resuscitators
• Key concerns — This equipment must be accessible instantly in an emergency. The case must be highly visible (bright orange or yellow) and have clear labeling. The equipment has expiration dates that must be visible. The case must be waterproof to protect the equipment from the elements
• Case design — High-visibility color (orange, yellow, or red), reflective tape (for visibility in low light), clear labeling (equipment name, expiration date, instructions), quick-release latch, waterproof (IP67), buoyant (if the case goes overboard, it should float)

Maintenance and Inspection Schedule

Marine cases require regular maintenance — the salt environment is unforgiving. Here’s a recommended inspection schedule:

• After every use — Rinse the case with fresh water (to remove salt), dry it thoroughly, leave it open to air out (to prevent mold and mildew), inspect the gasket for damage, check the drainage valve for debris
• Monthly — Inspect the gasket for compression set, cracks, and tears; check the latches and hinges for corrosion; inspect the case exterior for scratches and dents; test the drainage valve; verify the Gore-Tex vent is clear
• Every 6 months — Replace the gasket if compression set exceeds 25%; lubricate the latch springs with silicone spray; inspect the shock mounts for cracks and degradation; check the foam for water absorption and degradation; verify the IP rating with a water test
• Annually — Replace the gasket (regardless of condition — it’s cheap insurance); inspect the welds for cracks; check the powder coating for chips and touch up as needed; replace the casters if they’re worn; recalibrate any shock or vibration monitoring equipment

Marine and offshore environments are the ultimate test for equipment protection. Salt water, vibration, shock, humidity, UV, and mechanical damage — all at once, every day. A standard aluminum case with an EPDM sponge gasket will fail in months. A custom marine case with silicone gaskets, shock mounting, 316 stainless hardware, and closed-cell foam will last for years. The $150-$300 per-case premium for marine-grade construction is the cheapest insurance you can buy for a $10,000+ piece of equipment. Don’t learn that the hard way — specify marine-grade from the start.