Salt water is the worst normal environment an enclosure faces. Spray dries on the surfaces and leaves chloride behind. Humidity cycles every night, and anything not sealed properly eventually gets hosed down. A marine electrical enclosure therefore has to be chosen on three things at once: the rating, the material, and how you handle the moisture trapped inside.
The short answer: for electronics and a display on a boat, specify a 316L stainless enclosure, manufacturer-rated NEMA 4X-type / IP66 (not UL listed), sized with 25-30% spare space, with the display cut into the door as a factory window cutout. Our wall-mount line runs from 6 x 4 x 4 in to 60 x 36 x 16 in outside, in 304 or 316L, cut to your drawing and delivered in 10 business days from drawing approval.
What the boat environment demands
Start from where the box actually sits.
- Above decks, exposed: driving rain, salt spray, direct sun, possible hose-down. NEMA 4X-type sealing, 316L, UV-stable gasket, no bottom-facing penetrations.
- Below decks, dry locker: still humid, still salty air, less water. 316L still wins because the salt is already in the air; the rating can relax to splash protection if the location is genuinely dry.
- Engine room or near heat sources: add ambient temperature to the heat load calculation and check the electronics' maximum operating temperature.
Salt spray is the driver for material. Rain alone would not justify upgrading from 304. But chloride deposits on 304 in warm, humid coastal air cause tea-staining and pitting, as covered in our guide on whether 304 stainless can be used outdoors in coastal air. Once spray lands on the box regularly, 316L is the answer.
The rating it needs
For a box mounted on or near a deck, spec NEMA 4X-type. It covers falling rain, hose-directed water and splashing from any direction, and the X adds corrosion resistance to the type. Our wall-mount enclosures are manufacturer-rated NEMA 4X-type / IP66; they are not UL listed, and the ratings are manufacturer ratings.
Do not confuse this with submersion. IP68 and NEMA 6P are for equipment that can sit under water, which almost no boat electronics does. Continuous immersion is a different test and a different use case. For a chart-table or pilothouse box, 4X-type / IP66 is the right level, and the differences between the IP65 and IP66 water jet tests barely matter once salt corrosion is the real enemy.
One caution on paperwork: in US installations, NEC 110.28 states that IP ratings are not a substitute for enclosure type ratings. If a surveyor or inspector is involved, the NEMA-type number is what goes in the spec.
The material: 316L for anything near salt
The grades differ by one alloy addition, and it matters.
| Choice | Resistance to salt spray | Where it fits |
|---|---|---|
| 304 stainless | Good for rain and outdoor air; chlorides cause pitting and tea-staining | Inland, sheltered docks, fresh-water use |
| 316L stainless | Molybdenum markedly improves chloride pitting resistance | Salt spray, brine, coastal and on-board service |
Our full comparison of 304 vs 316L stainless for enclosures covers the metallurgy and the maintenance difference in detail. On a yacht, the box will see salt on its surface no matter how careful the crew is. 316L, rinsed occasionally with fresh water, stays clean; 304 in the same spot stains and pits.
The same logic applies to hardware around the box. Use 316 fasteners, and isolate the box from dissimilar metals where it mounts, because galvanic corrosion in a wet salt environment attacks the less noble metal quickly.
Sizing for electronics plus a display
Size the box from the inside out. Lay out the ARM board or mini PC, the power supply, terminal strips and any autopilot interface hardware on a backplate. Then add 25-30% spare width and depth for wiring, glands and future additions. The guide on how to size an electrical enclosure walks through the method; the short version is that wiring consumes far more volume than the boards do.
For a typical low-power marine PC build, three of our 316L wall-mount sizes cover most cases:
- 14 x 12 x 6 in 316L enclosure for a compact board set with a small supply, no door display.
- 16 x 16 x 6 in 316L enclosure, with door cutouts available for panel PCs from 7 to 10.4 in, if the display lives in the lid.
- 20 x 16 x 6 in 316L enclosure, door cut for panel PCs up to 11.6 in, when you also want a DIN rail of breakers or a terminal section inside.
Heat is rarely the problem with low-power electronics in a large steel box; steel conducts heat out well. Estimate it anyway. Dissipation in watts divided by the box's exposed surface area gives the internal temperature rise, and for a 20 x 16 x 6 in steel box roughly 30-50 W of load raises the interior only a few degrees over a 35 C ambient. If you move to higher-power gear, resize before you commit, because a hot sealed box on a warm deck is a different calculation.
The display and the window question
Two ways to give the crew a screen:
- The display mounts in the enclosure door, factory-cut for the exact panel PC model. The bezel and its gasket close the cutout, and the rating survives because the hole is cut and deburred before the gasket goes on. Check that the display itself is rated for the humidity and temperature swings inside a sealed box.
- The display sits outside the box on its own, and only the computing hardware goes inside. Simpler sealing, but then the display needs its own environmental protection, which is a separate purchase.
For anything a skipper touches with wet or salty fingers, pick a touch panel whose front is sealed to the same level as the box, and plan for salt film on the glass: a flat, sheltered mount wipes clean, a recessed one does not. If the screen must be readable in cockpit sunlight, brightness and mounting angle matter more than resolution, so check the display's nit rating before you cut the door.
Condensation: the problem the rating cannot fix
A perfectly sealed box traps the air you closed inside it. When the box cools at night on a boat, that air drops below its dew point and water condenses on the lid and the boards. No rating prevents this; it is covered in the guide on condensation in a sealed enclosure and in more depth in the condensation guide covering dew point, heaters and drains.
On a boat, the practical countermeasures are:
- Keep the box out of direct sun so the day-night temperature swing is smaller.
- Let the electronics' own waste heat hold the interior above the dew point; a box that runs daily usually stays dry inside.
- For a cold, intermittently used box, fit a small anti-condensation heater; the guide on when an outdoor enclosure needs an anti-condensation heater gives the sizing logic.
- Where the location allows it, fit a breather vent to equalize pressure and let humid air out; the condensation guide linked above explains when a vent or a drain is appropriate on a rated box.
Mounting and sealing on a moving platform
A boat vibrates, heels and slams. Mount the box on a bulkhead with the hinge side away from the prevailing spray direction. Bolt through the wall-mount feet rather than through the sealing surfaces, and use a thread sealant or well-placed gaskets on any fastener that pierces the shell. The article on mounting screws through an outdoor enclosure without leaks covers exactly this, and the broader guide on thin outdoor enclosure sealing explains how to plan the water barrier before you drill anything.
Cables enter through glands sized to the cable, never through unsealed knockouts. Our walkthrough on making an electrical enclosure waterproof with glands covers gland selection and torque. On a boat, prefer glands with an O-ring under the locknut and enough grip range for the actual cable diameter, because a gland on an undersized cable is the most common leak path we hear about.
Finally, bond the enclosure into the boat's grounding system per the marine electrical standard your surveyor works to. The principles in our guide on grounding and bonding an electrical enclosure apply, adapted to the vessel's bonding scheme.
What to put on the order
A marine enclosure order that builds right the first time includes:
| Item | What to specify |
|---|---|
| Material | 316L stainless, for any salt-spray exposure |
| Size | Outside dimensions with 25-30% spare internal space |
| Rating | Manufacturer-rated NEMA 4X-type / IP66; not UL listed |
| Door | Hinge side, latch type, and whether a display cutout is needed |
| Display cutout | Exact panel PC model and size, positioned for viewing angle |
| Cutouts | Every gland, connector and vent position with dimensions |
| Mounting | Wall-mount feet or other mounting style |
| Thermal | Heater or vent if the box sits cold or in sun |
We build to your drawing: you set the material, the dimensions and every cutout, we confirm the drawing with you, and the box is delivered in 10 business days anywhere in the world, counted from your approval of the drawing. Get the cutout positions right before you approve, because the box that arrives is the box you drew.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 14 × 12 × 6 in | 316L stainless | 14 x 12 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 16 × 6 in | 316L stainless | 16 x 16 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 6 in | 316L stainless | 20 x 16 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Is IP68 better than NEMA 4X for a marine enclosure?
Not necessarily. IP68 covers continuous immersion, which most boat electronics never see. A NEMA 4X-type enclosure handles hose-down, driving rain and salt spray, and the X adds the salt-spray corrosion requirement behind the rating. Match the rating to the mounting location: 4X-type above decks, and only consider submersion-rated boxes for equipment that can actually go under water.
Why 316L stainless instead of 304 on a boat?
304 stainless handles rain and outdoor air, but chlorides from salt spray attack it and cause tea-staining and pitting, especially in warm coastal air. 316L adds molybdenum, which markedly improves resistance to chloride pitting. For anything exposed to salt spray, brine or washdown with salt water, 316L is the grade to specify.
Can I mount a display in the enclosure door?
Yes. Order the enclosure with a window or display cutout in the door, cut before the gasket goes on, so the rating is preserved. The display bezel and its gasket then form the seal. Check the display's own temperature and humidity limits, because the inside of a sealed enclosure can be more humid than the chart table.
How do I stop condensation inside an enclosure on a boat?
A sealed box traps the moisture that was inside when the door was closed. As the temperature drops at night, that moisture condenses on the coolest surface. Fit a breather vent where the location allows, keep the box out of direct sun, and for electronics that run warm, let their heat hold the interior above the dew point. A small anti-condensation heater helps in boxes that sit cold.
What information does a custom enclosure order need?
Material grade, outside dimensions, door orientation, cutout locations with dimensions, window or display model, gland or connector positions, and mounting style. A dimensioned drawing approval is what starts the build on custom work, so get the cutout drawing right before you approve it.
