Boat Bible

After more than 40 years of research on the hulls of sailing yachts in the towing tank at Delft, boat expert Dr Lex Keuning bade farewell to TU Delft in June. His life’s work, the Delft Systematic Yacht Hull Series, is online.

Keuning (65) witnessed the start of the series as a student. That was in 1973, when Professor of Marine Hydrodynamics Jelle Gerritsma wanted to start taking comparative measurements of the hulls of sailing yachts. He collaborated with two colleagues from the Massachusetts Institute of Technology, with whom he shared a passion for sailing and sail boats: Professor of Marine Hydrodynamics Nick Newman and Professor of Hydraulic Engineering Justin Kerwin.

Their work had two objectives: (1) to create a simple calculation aid with which yacht designers could determine the nautical properties of their designs and (2) to develop a tool for identifying the weaknesses of various boats in sailing races. ‘For sailing yachts, it is much more difficult to calculate the expected speed than for motor yachts’, explains Keuning (3mE faculty) in his office next to the towing tank. ‘There are forces above and below the water that together create a complicated balance. This is difficult to calculate by hand. A programme was needed that could estimate a ship’s performance based on its length, breadth, depth and water displacement’.The research had to be systematic. In other words, it required variations on a standard ship. The choice at that time was the ‘Standfast 43’ by Frans Maas – a 13-metre long sailing yacht – for which a 1:6.25 scale model was made.

Keuning explains how the variations worked: ‘From the template of the mother ship, we made three models with slight increases and decreases in the breadth, each of which we then towed. Any differences that we measured would thus be due to the differences in breadth. This could also be done with length, depth and water displacement. It sounds simple, but when you change the breadth, water displacement changes as well. There are many mutual dependencies’. The first systematic series consisted of nine models.

The data from TU Delft form the foundation for performance prediction programs (PPPs), which yacht designers use during the design phase. One such designer is yacht builder Gerard Dijkstra, known for the clipper Stad Amsterdam from the VPRO TV programme ‘In het kielzog van Darwin’ (In the wake of Darwin). ‘The nice thing about the systematic series is that you don’t have to design based on a towable model’, explains Dijkstra. ‘You can create your own design according to your experience and your customer’s preferences in terms of length, breadth and depth. This forms the yacht’s operational profile. With WinDesign (one of the PPPs, ed.), you use this information to iteratively calculate the performance and adjust the design until you reach the best compromise that meets the client’s requirements. If you calculate the performance based on the series, you know that the ship will at least sail well’. Keuning has devoted the last two years to ensuring a smooth hand over of the project to his successor, Jasper den Ouden. Now he will have time to sail with his twin brother and others – not around the world, but to England and the Baltic Sea. That’s fine with him.

Lex Keining: “Voor zeiljachten is de snelheid die je kunt verwachten veel moeilijker uit te rekenen dan voor motorjachten.” (Foto: Sam Rentmeester)

Dr Lex Keuning: ‘For sailing yachts, it is much more difficult to calculate the expected speed than for motor yachts’.” (Photo: Sam Rentmeester)

Stay informed about the research

Receive the Delft Outlook newsletter 4 times a year