To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video Project 2.1: CFD prediction of a cruising yacht pitching in head seas Project 2.3: Bulb keel with streamlines Project 2.4: The Flying Optimist - an Optimist dinghy with foils     Photo: Per Thorén To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video Project 2.5: Free surface elevation behind the stern of a Finn Dinghy with a rudder oscillating +/- 15 degrees. Unsteady RANS prediction.

# Development of the equipment

​Project 2.1. is carried out in cooperation with the yacht Designer Gabriel Heyman, who designed three sailboat forebodies with different vertical distribution of fullness. These hulls were used in wave simulations with three different wave lengths in an MSc thesis by Kostalas and Pluto (2016).  A new validation case (towing in waves) was created in an MSc project by Myklebust (2017). New calculations for other wave heights were also carried out for the three hulls. A more thorough analysis of the validation is presently being carried out by Adam Persson in his PhD project. All systematic computations will also be repeated with a large emphasis on numerical details. The knowledge gained will be used in project 1.3.

Project 2.2. This ongoing project includes results from an MSc project by Allroth and Wu, reported in Allroth et al (2015) and from a PhD project by Orych, partly presented in Orych and Larsson (2015). The aim is to investigate the effect of the large transom sterns of modern hulls and to find the optimum stern and transom shape for varying Froude numbers.

Project 2.3. is based on a series of BSc and MSc theses and has recently been revisited. The objective is to investigate the performance of four types of contemporary keels for cruising sailing yachts. Three different bulb designs are compared with a plain fin and the results are evaluated as seconds per mile for a 40’ yacht equipped with the different keels. The effect of different materials (densities) in the fin and bulb is also investigated. Wind tunnel experiments, CFD computations and VPP predictions are used for the evaluation. A final journal paper on the work has now been published by Ljungqvist et al (2018).

Project 2.4. is on the design of hydrofoils for sailing yachts and dinghies. The first application was the Optimist. The objective was to show that foiling can be used even for very slow boats. The foils were designed in a Bachelor’s project by Andersson et al (2016), while the structural challenges were addressed in a student project by Blomstrand et al (2016). Wind tunnel tests were carried out for the sail and a towing tank test for the hull resistance. The final design was first evaluated in another towing tank test and finally in a successful test on the water, where the dinghy foiled perfectly. The hydrodynamic design is summarized in Andersson et al (2017) and the structural investigation in Blomstrand et al (2017). A journal paper was published by Andersson et al (2018). The Optimist and the foils used in the project were made in carbon fibre, and was therefore very expensive. So, in a follow-up BSc project a standard fibre glass Optimist was fitted with standard symmetric aluminium profiles and was shown to foil as well, albeit at a higher wind speed (Bergentz et al., 2018).

At present two MSc projects are underway, aimed at designing foils for a 7.5 m light-weight sailing yacht. In one project the foils are to be designed to passively control the ride height, while in the other project an active ride height mechanism is used.

Project 2.5. There are a number of rudder designs for the Finn Dinghy in use. The purpose of this project is to experimentally and numerically investigate the performance of the different designs in both steady and unsteady conditions. The project is not finished, but the status was presented at MARINE 2017, Persson et al (2017) and INNOVSAIL 17, Persson et al (2017b). The experimental part of the project has now been published as a journal article Persson et al (2018).

Project 2.6. An interesting FSI problem is the twist of a centreboard caused by the pressure distribution. With a proper structural design the centreboard will twist to windward at the tip, thus relieving the hull from some side force when sailing upwind. This will reduce the induced resistance. In an MSc project by Ekström and Forkman (2017) the limits for the twist and the corresponding resistance reduction were investigated.

Project 2.7. It is generally assumed that the slot between the foresail and the main causes an inverse Venturi effect, i.e. the flow velocity is reduced in the slot. This opinion is based on potential flow computations some 40 years ago with a large genoa overlapping the main. To investigate whether this assumption is true, particularly for modern foresails with less overlap, CFD computations were carried out for systematically varied overlaps. A number of other systematic variations in the sail plan were also made, such as its aspect ratio. The effect of a gap between the mast and the main was investigated as well in this MSc project by Jacobs and Sahlberg (2018).

Project 2.8. There is a wide-spread opinion among Finn dinghy sailors that a more flexible hull is faster than a more rigid one when sailing upwind in a seaway. This project aims at investigating this effect, both experimentally and computationally. In a set of wave tests in the SSPA towing tank, no differences between an extremely stiff hull and a standard hull was detected. However, the waves in the tests were rather small. New tests in larger waves will be carried out.

Project 2.9. There is an important interaction between a hydrofoil and a free surface. When the foil approaches the surface the latter will be deformed, which results in a reduction in lift. The deformation of the surface also generates a wave resistance. Further, the downwash from the foil changes, which has an effect on a downstream foil (stabilizer). These effects are important when designing foils for sailing yachts. In an MSc project by Andersson and Granli (2018) the free surface effect was analysed in detail using CFD and the effects could be explained.

Project 2.10. The scrapping of an increasing number of fibre glass yachts is a considerable environmental problem, so new environmentally friendly materials for yachts need to be developed. In this project various possible composites, like nanocrystalline cellulose fibres or flax fibres in a bio epoxy matrix are investigated. The test bench is the Optimist dinghy. A paper on the new material was presented at INNOVSAIL 17 by Finnsgård et al (2017). Recently, two Optimists have been built of recycled plastic material collected by young sailors around the Swedish coast. This is a cooperation project with the Swedish Yacht Racing Union.

Published: Mon 18 Sep 2017. Modified: Fri 22 Feb 2019