Two five-bladed stainless steel propellers made by direct metal laser sintering ran during free practice at the Peso da Régua round of the UIM F2 World Championship in September 2026, completing more than 60 laps between the boats of Owen Harwood and Ian Blacker. Dave Harwood’s Steel Developments built them with Caleb Jelf, a Mechanical Engineering student at Imperial College London who spent a placement year at the Mercedes-AMG PETRONAS F1 team in Brackley.
Jelf first proposed a printed race propeller to Harwood in 2024, when, he says, metal printing was “still largely a research subject with little industrial use.” He spent the following two years testing blade profiles on FDM plastic models before committing a shape to metal, and studying the elastic, strength and fatigue behaviour of DMLS parts.
The goal for this first pair was proving the material rather than chasing lap time. Jelf said the propellers were “about testing strength not speed,” but added that after initial testing the boats ran within five tenths of a second of the fastest propeller in that session.
DMLS builds parts by melting metal powder layer by layer inside an inert gas chamber, which lets a maker produce blade geometry that casting or machining can’t do economically. The tradeoff is proving fatigue life on a part under constant flexing and saltwater exposure, which is why Jelf’s two years of materials work came before any propeller touched a boat.
The next round of development will vary pitch, aspect ratio and diameter using a first-principles mathematical model, matched against Steel Developments’ existing dataset for the OptiMax 200XS engine, and extended to the new APX250 engine.