Everyone who has been in a traffic jam with a reasonably modern car knows that fuel consumption per kilometer is several times higher when you slowly push yourself forward than if you drive at 70 kilometers per hour. It works similar when it comes to shipping.
“There are opportunities to save fuel by reducing the speed of ships. But our interviews with shipping companies clearly show that greatly reduced speed does not necessarily lead to a large reduction in emissions, but even in some extreme cases increases emissions. However, in the models used to estimate the benefit of speed regulations, this knowledge is not always reflected”, Karl Jivén, a researcher at IVL Swedish Environmental Research Institute and one of the authors behind the pre-study Consequences of speed reductions for ships, says.
So it’s not a total surprpise that several sharp proposals for global mandatory speed reductions were presented by various parties within the IMO last year. But are they any good? The pre-study, which analyzes the most relevant proposals based on ten case studies and interviews with Swedish shipowners, shipping companies, suggests that mandatory speed limits for ships hardly will solve shipping's problems with climate emissions.
“The basic problem is that the connection used for ships' energy consumption presupposes that the effect is proportional to the speed in cubic meters. This is a good assumption when you are close to the speed at which a ship is designed. But when you lower the speed too much, other factors become important. The hull is not optimized for the speed, the engines have to work completely different, the propeller works worse and so on.”
The pre-study also shows that mandatory speed reductions can have significant economic logistical consequences for ship owners and their customers, especially in liner shipping.
“For example, if you have a loop that starts up in the Baltic Sea and goes down to southern Europe with stops in a certain number of ports for seven days, the whole setup will be jerked if you slow down. So from a business perspective, there will be very large consequences, both for shipowners and the export companies in Sweden. And when it comes to Ro-Pax, which goes to Germany and Denmark, the competition from road transport already is huge”, Catrin Lammgård, senior lecturer at the University of Gothenburg, who conducted the interview part of the study, says.
The shipping companies state that they have worked a lot in recent years with speed reductions and to find the optimal speed. Everyone of the interviewees was therefore negative about the proposals for mandatory speed reductions. Instead, the shipping companies want other types of policy instruments to be used to reduce greenhouse gas emissions.
An often-discussed issue is the possible effects of more vessels needed to be built when speed is lowered. An assessment performed for a Panamax tanker transport setup in a life cycle perspective indicates that the increased need for extra tonnage, when speed is lowered, will give a marginal effect on total greenhouse gases per transport work performed. This as the operational emissions connected to the consumption of fuel oil totally dominates the impact compared to building, mainting and scrapping a vessel.
The study was conducted by: Karl Jivén and Erik Fridell at the IVL Environmental Institute and Catrin Lammgård and Johan Woxenius at the School of Business, Economics and Law at the University of Gothenburg.