Getting started

  • Why is SumToZero's simulation software called Gomboc?

    When first used within Emirates Team New Zealand, it was simply known as "Dan's VPP". As its use grew, it clearly needed its own identity. Dan spent a weekend trying to come up with a catchy name, but the one he chose was ridiculed by the team, and will never be mentioned again!

    "So, what should we call it?" he asked. Steve Collie, an aerodynamics engineer in the team, did some Googling. He looked for something cool and unique relating to an equilibrium solution, and pronounced that it should be called "Gomboc"! The name stuck.

    As defined at, the 'Gömböc' is the first known homogenous object with one stable and one unstable equilibrium point, thus two equilibria altogether on a horizontal surface. It can be proven that no object with less than two equilibria exists.

  • What steering wheel can I use with Gomboc?

    To drive Gomboc in dynamics mode as a simulator, it's easiest to use a steering wheel. Any wheel that supports DirectInput can be used - although we may well be able to add a customisation to run something else.

    For a desk set-up, we recommend a Logitech G29, which is relatively inexpensive, has force feedback, and has plenty of buttons to which sail controls can be assigned.

  • Can I script Gomboc?

    Yes. Everything that can be done through Gomboc's GUI can also be scripted, either using Gomboc's internal JavaScript interface, or using its external API. Please get in touch for more details.

  • What support does my licence include?

    A paid Gomboc licence includes support to help you get set-up and answer any questions you have using the software, over the duration of the licence period.

    If you need more extensive support, for example, building models or making customisations to suit your project, this will be charged at 85 EUR/hour.

  • What skills or experience do I need to use Gomboc?

    To use Gomboc in dynamics mode, as a sailing simulator with an existing boat model, you need no experience at all - although some sailing skills would help!

    Running VPPs is a bit more involved, but once you understand the concepts of locking and unlocking parameters and choosing what you want to optimise, our GUI makes the process easy.

    Modifying foil shapes of an existing model to try and improve the design and estimate performance deltas is as simple as using CAD software. The process is quick to understand, but ultimately very powerful.

    Creating a model for a new boat requires editing text files, formatting input data, using software such as Rhino to prepare hull surfaces, and possibly writing some simple JavaScript code snippets. We are more than happy to help you with this if you need support.

  • I'm not confident building a model. Can you help?

    Yes, if you're not keen on building your own Gomboc boat model, we'd be very happy to build a model for you. Typically, it would take around 50 - 80 hours to build a model, and our time would be charged at 85 EUR/hour. However, it is very dependent on the data provided to us; a complete set of data clearly specified makes the job a lot easier!

  • How do I start modelling my boat?

    The easiest way is to start with an existing demo model supplied with Gomboc, then start modifying the different components. We can help you get started with this.

  • Can I integrate external results, such as CFD hull data, or sail data from North Sails, into a Gomboc model?

    Yes. Any data that provides forces - and optionally other outputs - as a function of parameters can be used. The data should be be organised into a PZ CSV format, where the columns represent parameters, forces and other outputs, and each row reports a condition (e.g. CFD run). As an example, you may have a matrix of 50 CFD runs for a hull. Columns could be Speed, Sink, Trim and Leeway as Parameters, and Fx, Fy, Fz, Mx, My, Mz as Outputs, and each row would represent the result of one CFD run. Additional columns might be Wetted Surface Area, Viscous Drag, Wave Drag, etc. These additional columns won't affect the Gomboc solution (unless you use them to compute some other forces) but will be output for information.

    Gomboc has several built-in methods for creating a smooth fit surface to the input data, and interpolating over that fit to estimate a solution at any combination of parameters.

  • What hardware do I need to run Gomboc?

    A Windows laptop or desktop PC - nothing special! A mid-range laptop is fine for creating models, running VPPs and dynamic simulations, but a machine with a faster processor will reduce VPP solution time and allow you to run smaller dynamic time-steps or a greater number of elements in appendage models. If getting the most out of the simulator graphics is important, a good graphics card is very worthwhile, and if using a VR headset it is essential.

  • Can Gomboc model my boat?

    Yes! Gomboc is completely customisable, and if your boat operates under the laws of physics, Gomboc can model it. We have standard modelling tools for appendages, sails, hulls, ocean waves and wind, but anything that falls outside the norm can be modelled by custom blocks or fitted-surface data. For instance, to add an outboard engine linked to a throttle parameter, all you need is an equation that describes the thrust generated as a function of boat speed and throttle, and a location in the model where that thrust should be applied. Then, if you want to steer by rotating your outboard, it's just a case of adding a rotating reference frame.

  • Licencing

  • Can I transfer my Gomboc licence to another machine?

    Yes. If you know in advance that you will be moving it from one machine to another, it's easier if you let us know before installing your first licence. We don't have an automatic procedure for removing a licence from an old machine, but can do this in a video call with you.

  • Can I model several boats using one licence

    Yes, with a full Gomboc licence you can model any number of boats, unless otherwise specified in the licence terms. However, if you only need the licence to model a specific boat, we can sometimes offer a discount for this case.

  • How much does Gomboc cost?

    Please get in touch with us and explain your use case!

    It is not reasonable for us to charge a hobbyist A-Cat designer the same as an America's Cup team, and like an architect's charges, the cost of our tools will relate to the value of the project or projects that you are using it for. We do strive to be completely fair and consistent across our customers.

    We are keen to expand our customer base, and don't want price to be an issue - but at the same time we want to be able to afford to keep developing the tools and support our users.

    We are happy to consider university licences at no charge.

  • What types of licence do you offer?

    We provide two main types of Gomboc licence:

    • A full design licence, where all of the features of Gomboc are unlocked
    • A Gomboc Player licence, which allows a specific boat model to be used in the simulator, but not modified. This is useful for a sailing team or boat owner who want to experience the behaviour and performance of their boat, but do not need to modify the design. It can also be useful for a design office working with Gomboc to supply a Gomboc Player licence to a client, for them to be involved in the design progress.

    Gomboc is licenced on an annual basis.