Developing an International Moth Testing Platform in a DVPP-Driven Real-Time Simulator

MSc Maritime Engineering Science – Yacht & High-Performance Craft
University of Southampton · 2024–2025

This project builds a full digital model of an International Moth dinghy inside Simulator in Motion (SiM), a Dynamic Velocity Prediction Program (DVPP) based sailing simulator. The platform is used to benchmark against D3-VPP® targets and to study two flight-control approaches: a mechanical wand and a heave PID controller.

Below you can explore the structure of the thesis, see selected plots, watch simulator runs, and access the full report, poster and references.

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Preview: Moth sailing downwind inside SiM

Explore the project

Use this overview to jump directly into specific parts of the work, similar to browsing chapters in an online book.

1. Introduction

Motivation, scope and specific objectives of using a DVPP-driven simulator as a test bench for the International Moth.

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2. Background & Literature Review

Hydrofoil history, sailing mechanics, Moth class rules, and the evolution from classical VPP tools to modern simulators.

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3. Methodology & Simulator

Modelling the Moth geometry and physics, setting up SiM, and building the workflow that links D3-VPP targets with the real-time model.

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4. Benchmarking vs. D3-VPP

How the simulator is validated by matching VPP targets at representative upwind and downwind operating points.

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5. Flight-Control Studies

Sensitivity studies for wand gearing, wand length, and heave PID gains, including comparisons between mechanical and electronic control.

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6. Conclusions & Future Work

Main findings, limitations of the present model, and suggested paths for further development of the platform.

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Abstract

The design of high-performance sailing craft has shifted from experience-driven iteration to data-driven workflows based on 3D modelling, computational fluid dynamics (CFD) and velocity prediction programmes (VPP). Hydro-foiling introduces inherently dynamic behaviours that exceed the scope of steady VPPs, motivating dynamic-DVPPs and simulators derived from them for design and training in America’s Cup (AC) and other high-performance contexts.

This thesis implements an International Moth inside Simulator In Motion (SiM)—a DVPP-based sailing simulator—aligning geometry, mass properties and aero/hydro models, and establishing a workflow to compare predicted performance and controller behaviour across configurations. Simulations were executed in this independent environment, while D3-VPP® targets and the Exploder MD3 geometry supplied by D3 Applied Technologies, S.L. (D3) defined the reference conditions and baseline configuration. The work first benchmarks SiM against D3-VPP targets at two representative operating points (best-VMG upwind and downwind, TWS = 14 kn), then exercises two flight-control approaches: (i) a mechanical wand (sensitivities to gearing and wand length) and (ii) a heave PID (sensitivities to Kp, Ki and Kd), in flat water and a simple regular sea state.

The simulator reproduces the VPP targets within ∼ 1% (speeds and VMGs), with attitudes close to target and force balances coherent at both points, supporting its credibility for controller studies in the tested envelope. For the wand, lower-response gearing attenuates wave-induced oscillations without degrading mean ride height, and increased wand length primarily biases the mean flight level while preserving a common steady wand angle. For the PID, a moderate tuning (baseline near Kp ≈ 4, Ki ≈ 2–3, Kd ≈ 6) offers the best compromise between rise time and damping; relative to the wand the PID shortens settling and improves disturbance rejection in both flat and waves. Notably, electronic ride-height control is currently prohibited by the International Moth Class Rules, restricting such benefits to non-official contexts.

Overall, the platform meets its objectives: it (i) matches VPP targets credibly at 14 kn upwind/downwind, (ii) captures expected controller trends (gearing, wand length, PID gains), and (iii) provides a practical, repeatable bench for flight-control development. Future work should broaden the envelope (TWS/TWA and irregular seas), refine wand mechanism modelling, and test crew dynamics and manoeuvres.

1. Introduction

Testing and developing components for foiling and high-performance boats is expensive and risky. Wind and waves constantly change, which makes it hard to compare configurations under controlled conditions. The International Moth, one of the most demanding foiling dinghies, is an ideal test case to explore how a DVPP-driven simulator can support design and control development.

The thesis defines three specific objectives:

2. Background & Literature Review

The background chapter starts with a short history of hydrofoils, from early experiments in the 19th and early 20th century to modern high-speed craft. It then reviews the basic sailing mechanics needed to understand the Moth: the wind triangle, force balances in the horizontal plane (XY) and vertical plane (YZ), and the role of foils, rig and hull.

A specific section is devoted to the International Moth Class Rules and to the mechanics of the flight-control system: bow-mounted wand, linkage, gearing, ride-height offset and rudder-rake mechanism. Finally, the chapter discusses classical Velocity Prediction Programs (VPP), their limitations in dynamic foiling regimes, and how DVPP-based simulators like SiM extend these tools into the time domain.

Velocity triangle and aerodynamic forces on a sailing yacht
Conceptual view of the velocity triangle and main aero/hydro forces on a sailing yacht. (Figure inspired by the material in the thesis.)

3. Methodology & Simulator Setup

The methodology chapter explains how the International Moth was translated into digital form. The work starts from geometry and mass properties (based on the Exploder MD3 configuration) and applies specialised physics models for foils, hull, rig, rudder and windage.

Inside Simulator in Motion (SiM), the project configures:

A step-by-step workflow links D3-VPP polars and VMG targets with SiM runs, making sure that both tools use consistent geometry, mass and operating conditions before any controller study is carried out.

International Moth running inside the SiM interface
International Moth geometry and forces running inside the SiM interface (illustrative figure based on the project poster).

4. Benchmarking against D3-VPP

Before using the simulator as a flight-control test bench, the model is benchmarked against D3-VPP at two representative conditions: best-VMG upwind and best-VMG downwind at TWS = 14 kn.

For each operating point, the study compares:

The SiM outputs match D3-VPP targets within around 1% in speed and VMG, and reproduce coherent attitudes and load distributions. This gives confidence that the simulator is a credible environment for controller studies within the tested envelope.

5. Flight-Control System Studies

Once the base Moth model is validated, the project focuses on the flight-control system. Two families of controllers are studied:

5.1 Sensitivity Studies

Several simulation campaigns explore how control parameters affect flight:

Simulator run – Downwind

International Moth sailing downwind inside SiM at the best-VMG operating point.

Simulator run – Upwind in waves

Upwind sailing with a regular head-sea wave, showing the interaction between sea state and flight-control settings.

On-water reference – Real Moth sailing

Short reference of a real International Moth foiling, used to keep the simulator behaviour connected to on-water experience.

5.2 Main findings from control comparisons

6. Conclusions & Future Work

The project shows that a DVPP-based simulator such as SiM can host a credible International Moth test platform. Within the tested envelope, the model reproduces D3-VPP performance, captures expected controller trends and provides a repeatable environment for flight-control development.

Limitations mainly concern the restricted operating range (TWS, TWA and sea states), simplified aero models and the absence of crew dynamics or manoeuvres. Future work should:

Within these limits, the SiM-Moth platform justifies its role as a development tool and opens the door to more systematic studies of foiling dinghy flight control and performance.

Additional material

Full thesis

Complete MSc report in PDF format, including all chapters, figures, tables and appendices.

Open full thesis (PDF)

Poster

One-page poster summarising motivation, objectives, methodology, key results and conclusions.

View project poster

Selected plots

External link with selected performance plots and comparison graphs used in the thesis.

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References

  1. I. Castañeda Sabadell, “Design of a physical and interactive real-time simulator based on a dynamic vpp as a support tool for sailing yacht design and operation,” Ph.D. dissertation, ETSI Navales, Universidad Politécnica de Madrid, 2018.
  2. J. Ozanne, Team principal at simulator in motion, simulator and a.i. team lead at alinghi red bull racing, https://www.linkedin.com/in/josephozanne/, Accessed: 2025-09-02, 2025.
  3. International Moth Class Association, International moth class rules, Dec. 2024. [Online]. Available: https://www.sailing.org/classes/moth/#Documents.
  4. International Hydrofoil Society, Aeromarine origins — early work by thomas moy (1861), Online article, Accessed 7 Sep 2025, 2018. [Online]. Available: https://www.foils.org/wp-content/uploads/2018/01/AeromarineOrigins.pdf.
  5. International Hydrofoil Society, Ships that fly — forlanini’s hydrofoil on lake maggiore (1906), Online booklet, Accessed 7 Sep 2025, 2018. [Online]. Available: https://www.foils.org/wp-content/uploads/2018/01/ShipsThatFly.pdf.
  6. Alexander Graham Bell Foundation, Hydrofoil history: Bell and baldwin’s hd–4, Web page, Accessed 7 Sep 2025, 2024. [Online]. Available: https://agbfoundation.ca/hydrofoil/.
  7. The Canadian Encyclopedia, Hydrofoil (historical overview and hd–4 record), Web page, Accessed 7 Sep 2025, 2023. [Online]. Available: https://thecanadianencyclopedia.ca/en/article/hydrofoil.
  8. T. M. Buermann, “An appraisal of hydrofoil supported craft,” SNAME Transactions, vol. 61, 1953. [Online]. Available: https://www.foils.org/wp-content/uploads/2018/01/SNAMEtransactionsVol61-1953.pdf.
  9. E. D’Amato et al., “Hydrodynamic design of fixed hydrofoils for planing craft,” Journal of Marine Science and Engineering, vol. 11, no. 2, p. 246, 2023. doi: 10.3390/jmse11020246. [Online]. Available: https://www.mdpi.com/2077-1312/11/2/246.
  10. L. Larsson, R. E. Eliasson, and M. Orych, Principles of Yacht Design, 5th. London: Adlard Coles / Bloomsbury, 2022, isbn: 9781472981929.
  11. J. I. R. Blake, Lecture notes on sess3027 yacht & high performance craft, Lecture notes, 2021.
  12. F. Fossati, Aero-hydrodynamics and the Performance of Sailing Yachts: The Science Behind Sailing Yachts and Their Design. London: A & C Black Publishers Ltd, 2009, p. 352, isbn: 9781408113387.
  13. B. Beaver and J. Zseleczky, “Full scale measurements on a hydrofoil international moth,” in SNAME Chesapeake Sailing Yacht Symposium, 2009, D021S002R006.
  14. Maguire Boats Ltd. “Main foil parts.” Product category page; photograph retrieved by author, Maguire Boats Ltd. (), [Online]. Available: https://maguireboats.com/main-foil-parts-23-c.asp (visited on 09/06/2025).
  15. F. Eggert, “Flight dynamics and stability of a hydrofoiling international moth with a dynamic velocity prediction program (dvpp),” M.S. thesis, Technische Universität Berlin, 2018.
  16. J. E. Kerwin, “A velocity prediction program for ocean racing yachts,” Rep 78-11 MIT, Jul. 1978.
  17. A. R. Claughton, J. F. Wellicome, and R. A. Shenoi, Sailing Yacht Design: Theory. Harlow: Addison Wesley Longman, 1998.
  18. A. R. Claughton, “Developments in the ims vpp formulations,” in Proceedings of the 14th Chesapeake Sailing Yacht Symposium, SNAME, Annapolis, MD, 1999.
  19. Orc vpp documentation, Technical description of the ORC Velocity Prediction Program, Offshore Racing Congress, 2020. [Online]. Available: https://www.orc.org/rules/.
  20. P. Kerdraon, B. Horel, P. Bot, A. Letourneur, and D. Le Touzé, “Development of a 6-dof dynamic velocity prediction program for offshore racing yachts,” Ocean Engineering, vol. 212, p. 107668, 2020. doi: 10.1016/j.oceaneng.2020.107668.
  21. D. P. J. Hull, “Speed sailing design & velocity prediction program,” BEng thesis, Australian Maritime College, University of Tasmania, 2014.
  22. N. Patterson and J. Binns, “Development of a six degree of freedom velocity prediction program for the foiling america’s cup vessels,” Journal of Sailing Technology, vol. 7, no. 1, pp. 120–151, 2022.
  23. A. Persson, “Predicting yacht performance in waves using a cfd velocity prediction program,” Ph.D. dissertation, Chalmers University of Technology, 2025.
  24. R. Tannenberg, S. R. Turnock, K. Hochkirch, and S. W. Boyd, “Vpp driven parametric design of ac75 hydrofoils,” Journal of Sailing Technology, vol. 8, no. 1, pp. 161–182, 2023.
  25. L. Sampedro Moix, “Preliminary design of a racing dinghy: F18 catamaran,” B.S. thesis, EPEF, Universidade da Coruña, 2023.
  26. S. Day, L. Letizia, and A. Stuart, “Vpp vs ppp: Challenges in the time-domain prediction of sailing yacht performance,” in Proceedings of the High Performance Yacht Design Conference (HPYD 1), Conference dates: 4–6 December 2002, Auckland, New Zealand: Royal Institution of Naval Architects (RINA), 2002. doi: 10.3940/rina.ya.2002.07.
  27. D. H. Harris, “Time domain simulation of a yacht sailing upwind in waves,” in Proceedings of the 17th Chesapeake Sailing Yacht Symposium, Annapolis, MD, USA: SNAME, Chesapeake Section, 2005, pp. 13–32.
  28. H. Hansen and et al., “Maneuver simulation and optimization for ac50 class,” in Journal of Sailing Technology, 2019. [Online]. Available: https://higherlogicdownload.s3.amazonaws.com/SNAME/1516f098-2760-4bff-86fa-9ca63a85f102/UploadedImages/2019%20-%2007%20__Hansen__et__al__Maneuver__Simulation__and__Optimisation__for__AC50_Class.pdf.
  29. M. F. Melis, “Velocity prediction program for a hydrofoiling lake racer,” Journal of Sailing Technology, 2022. [Online]. Available: https://www.foils.org/wp-content/uploads/2022/08/Melis-Submission-Hamburg-University-Honorable-Mention.pdf.
  30. K. Hochkirch, Fs-equilibrium user manual, Citado por Tannenberg (2023) como manual de referencia de FS-Equilibrium, DNV GL Maritime, 2018.
  31. M. Brito, “Use of gomboc to predict the performance of a hydro-foiled moth,” Yacht Research Unit, The University of Auckland, Tech. Rep., 2019.
  32. Simulator in Motion. “Demonstration video (homepage).” Frame captured by the author for academic illustration. (), [Online]. Available: https://www.simulatorinmotion.com/ (visited on 09/07/2025).