Salt Mist, IP66, and the Coating Spec
The first conformal coat passed lab spray tests and failed in service. The second passed in service and failed thermal cycling. The third one stuck.
A vehicle deck is not a chemistry lab. It is salt mist plus diesel residue plus brake dust plus thermal cycling, and a coating that passes one of those tests on a bench can fail the combined exposure in months. We learned this the slow way.
The three iterations
v1 — acrylic conformal
Passed salt-spray (ASTM B117) in the lab. In service, brake dust adhered to the surface and trapped moisture. Boards started showing leakage current within four months.
v2 — urethane conformal
Survived the brake-dust problem and the salt-mist problem. Failed thermal cycling at the connector joint over the first 30-day hot-route sailing — coating cracked, moisture wicked.
v3 — parylene + selective urethane
Conformal parylene under selective urethane at connector boundaries. Survived 14 months of pilot operation with zero coating-attributable failures.
How RoRoSAFE helps
The coating that survived is part of why RoRoSAFE's hardware is rated IP68 for salt fog, vibration and deck temperatures. For an operator, that means sensor cells that keep working through years of wet decks and thermal cycling, instead of a detection layer that degrades after its first season.
Pilot: one deck · installed alongside the berth · no drydock · 6 months of dashboard access
Sources
- ASTM B117 — standard practice for operating salt-spray (fog) apparatus.
- IEC 60068-2-11 and IEC 60068-2-52 — environmental testing: salt mist and cyclic salt-mist tests.
- IPC-CC-830 — qualification and performance of electrical insulating conformal coatings.
- IEC 60945 — general requirements for shipborne marine equipment (environmental and durability).
Questions, answered
Why did the conformal coating spec change twice?+
Because a vehicle deck is salt mist plus diesel residue plus brake dust plus thermal cycling, and a coating passing one bench test can fail the combined exposure in months. v1 acrylic passed salt-spray but trapped brake dust and leaked within four months; v2 urethane cracked at connector joints under thermal cycling; v3 parylene with selective urethane survived 14 months with zero coating failures.
Why isn't a lab salt-spray pass enough to qualify a coating?+
Because lab tests isolate single stressors. The acrylic v1 coating passed ASTM B117 salt-spray cleanly, then failed in service when brake dust adhered and trapped moisture — an interaction the lab test never reproduced. Coating spec is set by field data, with iteration cycles measured in months.
What coating finally worked for marine deck service?+
Conformal parylene under selective urethane at the connector boundaries. It survived 14 months of pilot operation with zero coating-attributable failures, after the earlier acrylic and urethane revisions each failed a different combined-exposure mode in service.
Continue the thread
Marine-Grade Cable Design for Decks
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Marine-Spec Thermal Cameras on Deck
The spec that decides fitment is not resolution. It is which EN 54 part the camera certifies to, because that fixes which FSS Code duty it can meet.
Redundant Power for the Segment Master
A segment master that loses power loses a whole deck. The redundancy story has to start at the supply rail, not at the network port.