New research shows that aircon can outstrip propulsion as the biggest energy user on yachts

The mystery of on-board energy use has been solved, according to speakers at a seminar on a new superyacht sustainability tool called Yeti. Aircon may consume more energy than propulsion over the course of a year, and even banal galley equipment has a much larger impact than previously thought.

These and other findings were presented at the second of six seminars organised for industry insiders by the Water Revolution Foundation (WRF). The events are to introduce the WRF’s Yacht Environmental Transparency Index (Yeti), which aims to give new and existing yachts a detailed sustainability score. The process is backed by 18 of the biggest names in superyachting, including Heesen Yachts.

Developing an operational profile
Using publicly available AIS data that records a yacht’s position, course and speed, the Yeti team analysed the usage profile of 103 private yachts. They were selected by WRF to represent a cross-section of the fleet in terms of size, age, type and location, and their data crunched over the six years from 2015-2020. The result was nearly 300 yacht-years of intelligence.

“What we found is that yachts spend a significant amount of time stationary, either in port or at anchor,” explained Enrico della Vallentina, a team leader at maritime research institute Marin operating within the Yeti group. “They spend just 10% of their time being propelled, and only 0.1% of their time at maximum speed. This underlines the importance of optimising hulls for cruising speed.”

It is a stark contrast to the operational profile of a commercial vessel, which aims to spend as much time as possible under way. “Existing regulations need a custom adjustment to fit the operational profile of yachts,” asserted Hanna Dubrowska, technical director of WRF. “Some 50-75 per cent of a yacht’s energy is used for hotel load, the rest for propulsion.”

Hotel loads under the spotlight
Understandably, then, hotel power generation and use has been a major focus for the Yeti group. There are so many entrenched views among different parts of the industry, that it has required the cold blade of a rigorously scientific process to cut through and make progress.

Marine engineer Jaime Barros at WRF explained the process of getting to the bottom of what he called the ‘hotel load mystery’. “I started digging into load balances – a list of all electric power consumers on board – by analysing more than 30 of them on existing yachts. The result was a formula correlating to the major parameters of a yacht. One of the surprises was the consistent findings on usage of galley equipment and aircon in port.”

It has long been known that aircon is a big consumer of energy on yachts, but Barros found that it accounted for an average of 20-30% of total energy on board. In some cases, it even exceeded the power used for propulsion. This puts the focus squarely on waste heat recovery, insulation and glazing as ways to lower the overall energy load.

Galley equipment was another surprising finding. On several yachts in the study, dormant fridges and freezers consumed over 20% of the shore power load. On one notable outlier, the galley consumed nearly 45% of the yacht’s power on the dock.

Barros is helping the Yeti group to develop a standardised load balance sheet so that boatbuilders can start to benefit from the findings. This will even take into account the energy mix behind the shorepower of different yachting hotspots. For instance, Montenegro, Turkey and Jamaica have among the most polluting electricity generation systems, while France, Monaco and Colombia are among the least. “These insights will help to make better choices during the design and engineering phases,” he added.

Heesen Yachts is one of the founder members of the Yeti group, which was born in 2019 out of an industry consensus to improve sustainability. CEO Niels Vaessen believes it is vital work. “Our industry is always cautious about change, because safety and reliability is so critical to our success,” he said. “By working scientifically across such a broad cross-section of the superyacht industry, Yeti is making much faster progress than any individual member could have achieved by themselves. This is critical to the industry’s long-term future.”

The Yeti tool is designed to assess a yacht’s overall sustainability score and identify areas where the biggest efficiency gains can be made. It can be used for refit projects and the existing fleet, as well as for new builds and sailing superyachts. Individual yacht owners can also request a sustainability score for their yacht by contacting the WRF.

Words by Sam Fortescue.