Opposite: Silver medallists Keiju Okada and Miho Yoshioka went to the Paris 2024 Olympic regatta as reigning world champions in the Mixed 470 class, their latest Pearson hull and foils benefiting from detailed CFD and tank studies by the author’s ACT Technologies. The now married Japanese pair had competed separately at several previous Olympic regattas in the 470, in the Women’s and Men’s categories. Like the Finn and Flying Dutchman classes, the 470 one-design class rules incorporate just enough by way of tolerances in design and build to ensure development never ceases to be a hot topic. Funky new Snipe bow treatment (above), again from ACT
Commercial vessels CFD for commercial ships began to be applied around the same time as for racing yachts. Since there are no significant changes in the hull’s attitude as seen in yachts, calculations are typically performed more quickly and with the ship in an upright position. However, self-propulsion calculations must now be introduced to account for the resistance increase due to propeller rotation, as well as the propeller efficiency itself as affected by the ship’s stern wake. Even if hull resistance is low, poor self-propulsion characteristics can lead to higher power requirements, so a design balancing resistance and self-propul- sion elements is necessary. According to the IMO regulations that
came into effect on 1 January 2013, vessels that entered new construction contracts on or after this date or those delivered on or after 1 July 2015 must meet the Energy Efficiency Design Index (EEDI) require- ments which specify the maximum
allowed CO2 emissions per ton-mile of cargo for different types of ships. Post-2018 EEDI Phase 2 required a 20%
reduction from the previous reference line, and a 30% reduction is required from 2025. Consequently, the importance of
CFD is increasing as ship design optimisa- tion and fuel efficiency technologies are actively developed. Previously CFD devel- opment focused primarily on model-scale tank testing but, as with some well-known scaling issues in yacht design, critical dis- crepancies between estimated and actual power requirements for full-scale ships have also arisen. However, with the latest advancements in computing power, CFD development modelled at full-scale is now also beginning to be within reach.
Wind-assisted commercial vessels In response to EEDI regulations, projects utilising traditional sailing technologies have become increasingly common over the past decade. One such project I am involved in is called Wind Challenger, which involves equipping commercial ships with rigid sails approximately 50m in height, reducing fuel consumption by measurable worthwhile amounts. The ‘sails’ are equipped with a telescop-
ing mechanism that allows them to extend and retract vertically for reefing and stor- age. Additionally, we succeeded in develop- ing a crescent-shaped cross-section profile which enhances lift by allowing a larger camber. This enables the single wing to
generate lift comparable to a wing with flaps. Using multiple rigid sails, the interfer-
ence between the sails in the fore and aft axis is significant. Therefore, it is crucial to find the optimal sail angle for each wind direction (AWA) to achieve best perfor- mance, which again we determine using CFD. The forces estimated from the sails and the forces on the hull and rudder below the waterline must of course balance out, which in turn determines the hull’s drift (leeway) angle, rudder angle, speed and fuel consumption. A program similar to a yacht VPP is
now required, which we named the Energy Prediction Program (EEP). This calculates performance for various wind directions and speeds, allowing accurate estimations of fuel savings using a routeing program tailored to common commercial routes. We are currently also working with
another project, Wind Hunter, which further extends applications of rigid sails. This involves a ship powered solely by wind, with a turbine installed underwater to gen- erate electricity and produce hydrogen. The generated hydrogen is stored by combining it with toluene. When the storage is full the ship returns to port to unload the tank and then heads to another location with wind
SEAHORSE 51
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