Why do shipyards still lose days to cable data that doesn't add up?

Ask any electrical engineer in a shipyard what really eats their week, and you rarely hear "routing math." You hear something quieter and more frustrating: the numbers don't match. The cable schedule says one thing, the tray drawing says another, and the BOM insists on a third. So they spend a day chasing which one is right.

It sounds trivial. It isn't. A modern vessel can carry hundreds of thousands of meters of cable, and the electrical design touches almost every compartment on board. When the data behind it drifts even slightly, the cost shows up late — usually during a class-society survey, which is the worst possible moment to discover that a tray is over-filled.

The small number that breaks everything

Here's a concrete example. Every cable has an outer diameter (OD). It feels like a minor catalog detail, but OD is the single input that drives the tray fill ratio — how much of a tray's cross-section the bundle actually occupies. IEC 61537 sets the limits, and surveyors check them.

Now suppose one cable type was entered with the wrong OD, off by a couple of millimeters. Nothing looks broken. The schedule still validates. But that error quietly inflates or deflates the fill percentage on every tray that cable runs through. Tray sizing shifts. BOM quantities shift. And the day the surveyor walks the route with a tape measure, the paperwork and the steel disagree. Multiply that by a few hundred cable types and you understand why "the numbers don't add up" is a recurring line item in shipyard schedules.

Why spreadsheets quietly make it worse

Most of this work still lives in spreadsheets, and spreadsheets are brilliant at one thing engineers don't actually want here: letting every value be independent. A cable's OD in the schedule has no idea that the same cable's OD in the tray-fill sheet exists. Change one, and the other stays stale. There's no single source of truth — there are dozens, and they drift apart the moment two people open two files.

That isn't a discipline problem. It's a structural one. You can't audit your way out of a system that has no enforced relationships between the cable, the tray it sits in, the drum it's pulled from, and the document that approves it.

What "fixing it" actually looks like

The fix is boring in the best way: make the data relational and let the calculations live next to it. When the cable's OD is defined once and every tray-fill, BOM, and drum figure reads from that one definition, a wrong number can't hide. Change the OD, and the fill ratio, the tray recommendation, and the material count all update together — or flag a conflict.

• One cable type, one OD, referenced everywhere downstream.
• Tray fill validated against IEC 61537 automatically, not by hand.
• Class checks (DNV, LR, ABS, KR, BV) run on the live data, not a snapshot from last week.
• Drawings and approvals kept in step with the electrical design, not in a separate inbox.

This is exactly the gap SEcMS (secms.tech) was built to close on the electrical side — cable routing, tray fill, BOM, drum planning and class checks in one browser-based system, no installation. Its sister platform SEDMS (sedms.app) does the same for shipyard drawings and distribution documents, so the revision you're routing against is the revision that's actually approved. Together they keep the two halves — the electrical data and the documents that govern it — from drifting apart.

The honest part

No tool deletes the underlying complexity of marine electrical design. SOLAS still demands fire-segregated routing, class societies still want their margins, and a 174K LNG carrier is still a hard problem. What good tooling removes is the self-inflicted part — the day lost to reconciling three numbers that should never have been allowed to disagree in the first place. That day, repeated across a project, is where the real savings hide.