Shipbuilding Laser Cutting: Thick Plate Guide

In short: For shipbuilding, the hard question is edge acceptance, not whether a fiber laser can cut the plate.

High-power lasers now reach the 12–40 mm range that one laser maker gives as typical for shipyards. But the current IACS quality standard sets roughness limits for gas cutting only and does not mention laser cutting. Agree your cutting procedure with your class society before you buy, then test your own steel.

What the ship quality standard says

IACS Recommendation 47, the Shipbuilding and Repair Quality Standard (Rev.10 Corr.1, October 2025), gives guidance on hull quality where no recognised shipbuilding or national standard accepted by the class society exists (source 1). We searched the full text. It has a section on gas cutting, and the word "laser" does not appear. These are its roughness figures:

Cut edge	Member	Standard	Limit
Free edge	Strength members	150 µm	300 µm
Free edge	Others	500 µm	1,000 µm
Welding edge	Strength members	400 µm	800 µm
Welding edge	Others	800 µm	1,500 µm

IACS Rec. 47 Rev.10 Corr.1, Part A, section 5, Gas Cutting (source 1).

That does not ban laser cutting. It means there is no fixed laser figure in this document, and other parts of it decide the route:

Paragraph 1.4: procedures the standard does not cover are to be approved by the class society, based on procedure qualifications and/or recognised national standards.
Paragraph 1.3: a stricter standard may be required for critical and highly stressed areas.
Section 8: edge preparation is to be qualified under IACS UR W28 or another recognised standard.
Scope: it generally does not apply to special ships such as gas tankers, or to stainless steel structures.

Each class society also has its own rules, and we have not reviewed them all. Ask your surveyor what evidence is needed before you choose a machine. Approval sits between your yard and your class society, so a machine brochure will not settle it.

How thick can a fiber laser cut?

Published figures vary, because they measure different things:

Source	Set-up	Reported result	How to read it
The Fabricator, 2023 (source 2)	30 kW fiber laser at a US fabricator	19 mm (3/4 in.) steel at about 5.8 m/min; 16 mm (5/8 in.) at about 7.4 m/min	Shop report on production work
Lopez et al., 2017 (source 3)	10 kW fiber laser, S355 steel	Cut a 70 mm section; focal position had the strongest effect on kerf width	Nuclear dismantling research. It shows reach, not a ship-quality edge
The Fabricator, 2014 (source 4)	Laser vs 400 A high-definition plasma, 25 mm plate	Laser about 0.9 m/min; plasma about 2.3 m/min	Figures from a machine maker, before today's power levels
Physik Journal, 2026 (source 5)	20–60 kW fiber lasers	Up to 40–50 mm at acceptable quality; over 80 mm in controlled conditions, at reduced speed	Author works for a laser source maker. Treat as a maker's claim

Speeds converted from inches per minute.

The same maker's article says shipyards typically cut very large plates, 12–40 mm thick, on large-format machines (source 5). It says lasers keep a speed lead over high-definition plasma at 40 mm, with a shrinking margin, and that plasma remains viable at low utilisation (source 5). We found no independent side-by-side test at 40 mm, so run your own thickness on both processes.

Assist gas matters too. That article gives mixed gas as typical up to about 20 mm at 20 kW and about 40 mm at 40 kW. Beyond that, pure oxygen is generally required and the speed gain falls (source 5).

Does a laser edge affect fatigue strength?

Hull structures carry repeated loads, so the cut edge matters as well as the speed. Two open studies are useful, with limits:

Diekhoff et al., 2020 (source 6): 8 mm S355M and S690Q cut by oxygen, plasma, laser and waterjet. All series exceeded fatigue class FAT100 and could be classed FAT125. The authors found only a weak link between ISO 9013 quality groups and fatigue strength. Slower cutting reduced roughness and raised fatigue strength in every tested series.
Rowiński, 2021 (source 7): 10 mm S355J2N cut by waterjet, oxyacetylene and plasma; laser was not tested. Plasma gave the smoothest edge but the lowest fatigue category, 146 MPa against 226 MPa for oxyacetylene. Average edge hardness was 310 HV10 for plasma and 244 HV10 for oxyacetylene.

The lesson is that a smooth edge does not prove fatigue strength; hardness and process conditions count as well. Both studies used thin plate and small specimens. We found no published fatigue study of fiber-cut shipbuilding grades such as EH36 at 20–40 mm, so your own qualification tests matter.

Bevels and weld preparation

Rec. 47 lists typical butt weld edge preparations, and those edges have to be qualified (source 1). Yards have looked at laser bevels for a long time. A 2004 article by a laser maker's engineer describes a laser-assisted oxygen process installed at a US shipyard in 2002, and trials on 26 and 30 mm steel at 15–45° bevels, with a 2–3 mm kerf. It also says those bevels cost more than conventional methods (source 8). That process is old, so read it as history. For today's options, see laser vs plasma bevel cutting. Our HL-F series offers a bevel head as an option; test your own joint before relying on it.

Plate condition and piercing

Plate that has stood outdoors is a real issue. One heavy equipment maker found that rust spots caused poor edges or incomplete cuts, and it stopped storing steel outside when it moved to laser (source 9). If your plate is primed or weathered, test it in that state.

Piercing also counts on thick plate. The 2014 report describes a long pierce of 20–25 seconds on 25 mm plate, which added cycle time and heat that could cause distortion (source 4). Count pierces per part in any speed comparison, and check that the bed fits your largest plate. HL-F beds run up to 12 × 2.5 m.

Laser, plasma or oxy-fuel: choose by job

Job	Start with	Why
Parts with small holes and tight fit-up, up to about 25 mm	Fiber laser	Accuracy and fewer secondary operations (sources 2, 5)
Long, simple profiles at low utilisation	Plasma or oxy-fuel	Lower capital cost (source 5)
40 mm and above	Test laser against your current process	Speed lead narrows; oxygen cutting needed (source 5)
Weld bevels	Test on your joint	Qualification is required (source 1)
Critical, highly stressed areas	Agree with class first	A stricter standard may apply (source 1)

Summary by Halcyon Laser. Starting points, not class guidance.

Before you buy

Ask your class society in writing what evidence it needs for laser-cut edges.
List plate by grade, thickness and tonnes per month.
Cut samples in the state you use them, including any primer.
Measure roughness and perpendicularity against ISO 9013, and edge hardness.
Run your welding procedure tests on laser-cut edges.
Work out shifts and utilisation, since the cost case depends on them.
Send drawings through our test cut request and compare against your current edge.

We hold no class approval for a cutting procedure, and this page is not class advice.

Frequently asked questions

Does IACS Rec. 47 allow laser cutting?

The current Rev.10 Corr.1 gives roughness limits for gas cutting and does not mention laser. Procedures it does not cover are to be approved by the class society, based on procedure qualifications or recognised national standards.

How thick is plate in shipbuilding?

One laser maker gives 12–40 mm as typical for shipyard plate, cut on large-format machines. Check your own plate list, since ship type and structure change the range.

Is laser or plasma faster on thick ship plate?

It depends on power and thickness. A 2014 report put plasma ahead on 25 mm plate. A 30 kW laser has since reached about 5.8 m/min on 19 mm steel. Test your own thickness on both.

Do laser cut edges hurt fatigue strength?

In one study on 8 mm S355M and S690Q, all cut methods reached at least FAT125. Roughness alone did not predict results. We found no equivalent study on thick shipbuilding grades, so test your own.

Does Halcyon Laser have class approval?

No. Approval of a cutting procedure sits between the yard and its class society. We can supply test cuts for your qualification work.

Next step

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Sources

IACS Recommendation 47, Shipbuilding and Repair Quality Standard, Rev.10 Corr.1, October 2025 (classification societies’ association; PDF read and searched) — iacs.org.uk (accessed 2026-11-01)
Tim Heston, “The business case for investing in high-powered laser cutting”, The Fabricator, 13 October 2023 — www.thefabricator.com (accessed 2026-11-01)
A. B. Lopez, E. Assunção, L. Quintino, J. Blackburn, A. Khan, “High-power fiber laser cutting parameter optimization for nuclear decommissioning”, Nuclear Engineering and Technology 49 (2017) 865–872 (Universidade de Lisboa, TWI) — koreascience.kr (accessed 2026-11-01)
Tim Heston, “Plasma cutting or laser cutting? How about both?”, The Fabricator, 22 October 2014 (speed figures from a machine maker’s vice president) — www.thefabricator.com (accessed 2026-11-01)
Fahrettin Ucar, “Advantages of ultrahigh-power laser cutting over plasma cutting”, Physik Journal Best of, April 2026 (maker’s view: author from IPG Photonics) — pro-physik.de (accessed 2026-11-01)
P. Diekhoff, J. Hensel, T. Nitschke-Pagel, K. Dilger, “Investigation on fatigue strength of cut edges produced by various cutting methods for high-strength steels”, Welding in the World, 2020 — link.springer.com (accessed 2026-11-01)
S. Rowiński, “Effect of Steel-Cutting Technology on Fatigue Strength of Steel Structures: Tests and Analyses”, Materials 14(20):6097, 2021 (Wrocław University of Science and Technology) — pmc.ncbi.nlm.nih.gov (accessed 2026-11-01)
Jack Gabzdyl, “Cutting on edge”, Laser Focus World, 1 June 2004 (author from TRUMPF, a laser maker) — laserfocusworld.com (accessed 2026-11-01)
“Agriculture equipment manufacturer cultivates productivity improvements with laser technology”, The Fabricator, 25 September 2003 — www.thefabricator.com (accessed 2026-11-01)

Laser cutting thick plate for shipbuilding