Marine, Offshore, and Underwater Cases: A Complete Guide

A subsea robotics company in Houston was shipping their remotely operated vehicle (ROV) control station from Texas to an offshore oil rig in the Gulf of Mexico. The control console — a custom-built unit with monitors, joysticks, and signal processors — was packed in a standard 4mm aluminum case with foam padding. It survived the truck to the port fine. But between the port and the rig, the case was exposed to salt spray on the helideck, and when the ROV technician opened it on the rig, the case interior was damp, the monitor bezel had light corrosion, and the foam was holding salt residue. The control station itself was fine, but the case had rust stains on the outside and the foam would need replacement before the next shipment. A $3,200 case job turned into a $600 foam replacement plus a week of drying time. That’s what happens when you use a general-purpose aluminum case for a marine application.

Marine, offshore, and underwater equipment cases don’t just hold gear. They have to survive salt spray, humidity, temperature swings, vibration, and sometimes actual immersion. The equipment inside — ROV controls, sonar units, dive computers, navigation instruments, water quality sensors — is expensive, mission-critical, and often needed on short notice. The case that gets it there has to be engineered for that environment.

Why Marine and Offshore Is a Different Case Game

Salt air does three things to an aluminum case that normal industrial air doesn’t:

• Accelerated galvanic corrosion — When dissimilar metals touch in the presence of salt water, one becomes an anode and corrodes. Steel hardware on aluminum panels, zinc-plated brackets in contact with bare aluminum — these are corrosion cells waiting to happen. In a normal warehouse, this process takes years. On a rig helideck, it takes months
• Hygroscopic moisture — Salt-laden air holds more moisture, and that moisture gets drawn into the case through the gasket every time the temperature cycles. Closed-cell foam resists absorption but still traps condensation between the foam and the equipment
• Biological growth — On boats and offshore platforms, mold, mildew, and marine biofilm grow on any surface that stays damp. This is cosmetic at best, structural at worst — mold eats through adhesives and causes foam delamination

Add to that the reality of offshore logistics: cases get loaded onto supply boats, dropped on deck, exposed to rain, and sometimes moved by crane. A case that survives a warehouse forklift doesn’t necessarily survive a crane lift at sea in a 4-foot swell.

Marine Case Specification: What Actually Matters

1. Material Selection

• 5052-H32 aluminum — The standard for marine applications. Better corrosion resistance than 6061, good formability, and sufficient strength for case walls. 3003 aluminum is acceptable for lighter-duty use but 5052 is the right choice for offshore
• 6061-T6 aluminum — Stronger but more prone to galvanic corrosion in marine environments. If you use it, specify chromate conversion coating before powder coat
• Stainless steel hardware only — 316 stainless is the minimum for saltwater exposure. 304 stainless will rust in a marine environment within 12-18 months. 316 has 2-3% molybdenum which dramatically improves pitting resistance
• Hardware isolation — Even with 316 stainless, use neoprene or plastic washers between stainless and aluminum to prevent galvanic corrosion at the fastener interface

2. Surface Treatment

• External finish — Marine-grade powder coat (polyester, 60-80μm minimum) over chromate conversion coating. Anodizing is acceptable but can chip; powder coat is more durable for case exteriors that get bumped against railings
• Internal finish — Bare aluminum with chromate conversion, or epoxy powder coat. Don’t use paint inside the case — it chips and creates corrosion sites
• Gasket surfaces — Must be bare aluminum (no paint) for a consistent seal. The gasket groove should be machined after finishing, not before

3. Sealing and Ventilation

• IP rating — For deck use: IP65 minimum. For engine room or below-deck use: IP54 may be acceptable. For dive equipment or immersion use: IP67 or IP68, with vent plugs
• Vent plug — Every marine case needs one. ePTFE (Gore-Tex) vent plugs allow pressure equalization while blocking liquid water. Without it, the case “breathes” as it heats and cools, drawing in moist salt air through the gasket. With it, the case stays at ambient pressure and the gasket stays dry
• Gasket material — EPDM only. Silicone is acceptable for high-temperature areas but has higher compression set. NBR and neoprene degrade faster in UV and salt exposure

4. Foam Selection

• Closed-cell EVA (60-80kg/m³) — The right choice for marine cases. Resists water absorption, doesn’t support mold growth, and provides good shock absorption
• Open-cell foam — Never use in a marine case. It absorbs water like a sponge and holds it against the equipment
• PE pluck foam — Acceptable for dry deck use but compresses faster than EVA. Not recommended for offshore service
• Foam adhesive — Use marine-grade contact adhesive (not standard craft adhesive). Standard adhesives break down in humidity and cause foam delamination

Underwater and Dive Equipment Cases

Dive computers, underwater cameras, sonar units, and ROV components have additional requirements beyond standard marine cases:

• Floatation option — If the case is accidentally dropped overboard, does it float? For dive equipment, we can add floatation blocks to the case walls. This is a safety feature — a $15,000 underwater camera system that sinks is gone forever
• Pressure rating — If the case is going on dive missions, specify the depth rating. A case rated IP67 at 1m for 30 minutes is not the same as one designed to withstand 10m depth on a dive. The panel thickness, gasket compression, and latch strength all change
• Corrosion of fasteners inside the case — Even with a sealed case, condensation forms. Stainless steel fasteners inside the case should also be 316 grade. Steel screws holding the foam in place will rust and stain the foam and the equipment

Specification Comparison: Marine Case Grades

Offshore Logistics and Handling

Offshore equipment moves through a rough chain: warehouse → truck → port supply boat → crane to rig → storage on rig → deployment. Each step has its own hazards:

• Crane lifting — If the case is being lifted by crane, it needs lifting eyes that are through-bolted (not surface-mounted) and rated for the case weight plus safety margin. A $5,000 case falling 20 meters from a crane hook is catastrophic
• Deck stacking — On supply vessels, cases get stacked on deck in all weather. The case lid must support at least 3x its own weight without flexing. This is why 4-5mm panels are the minimum for offshore use
• Rough handling — Offshore workers don’t have time for gentle handling. Cases get thrown onto skids, slid across grating, and bumped against railings. Corner protectors and edge trim aren’t optional — they’re survival features
• Identification — Every case needs a stainless steel ID plate (not adhesive labels) with case number, contents, weight, and handling instructions. Adhesive labels fall off within a month in salt air

We’ve built marine cases for ROV control stations, offshore sensor kits, dive equipment, naval sonar units, and coastal weather stations. The principle is always the same: the marine environment punishes every shortcut in material selection, hardware grade, and sealing. Build it right the first time, and it lasts. Build it cheap, and you’ll rebuild it in 18 months.