Abstract
Dr Elizabeth Lindstad from Norwegian marine research organisation Sintef Ocean, notes that while ships’ fuel consumption is minimised when they are travelling at the optimum speed which they were designed for, the fuel savings from slowing steaming are greatest when pulling back from the highest speeds. She gives the example of a fully-laden 63,000 dwt Supramax bulker running on a fuel priced at USD500/t. Slowing from 15 to 12.5 knots would typically reduce fuel consumption by around 25kg per nautical mile, from 180 kg/nm to 155kg/nm. Yet reducing speeds further from 12.5 knots to 10 knots only reduces fuel consumption by around 10kg/nm, from 155kg/nm to around 145kg/nm. “When you start to push an engine beyond its sensible speed, the power consumption increases a very large amount,” she said. Her calculations show that for the Supramax, the optimal speed is around 9 knots at fuel consumption of 137.5 kg/nm, and that moving in either direction away from this increases fuel consumption. “It’s the same as your car. The lowest fuel consumption is probably around 40 mph. If you go slower than this the consumption per mile will increase, but it will be quite flat from 40mph to 60mph. Above that it really starts to increase.” This concept applies equally to bulkers and tankers, as well as cars.
In addition to this, Lindstad notes that there are other factors that contribute to overall cost of each vessel journey, such as newbuilding costs, Capex, Opex and time charter costs, as well as bunker fuel. Vessels can slow down, saving on their bunker fuel costs, but this means that many of these expenses are higher per voyage, as takes longer for the vessel to reach its destination. For this reason, she calculates that the speed that gives the lowest overall cost per nautical mile for the Supramax would be 12.5 knots, giving it a cost per mile of around USD112/nm. If the vessel were to slow down, the cost per nautical mile would rise significantly – with the costs increasing exponentially the slower the vessel goes. Slowing from 12.5knots to 10 knots would increase the cost by only around USD5/nm, for example, but slowing down a further 2.5 knots from this to 7.5 knots would increase it by USD22.5/nm, from USD115/nm to USD137.5/nm.
This does not mean that vessels will not slow steam on ballast voyages, she notes, but this would reflect ships operating in a weak market deliberately slowing down in order to take capacity out of the market, instead of acting to save fuel. “In reality consumption is also lower in ballast, so it doesn’t make sense to slow steam on the ballast leg to save money. But it does make sense to slow steam to take capacity out of the market. On your loading legs you have your contractual obligations, so to go slowly would be expensive.”
Given that vessels are in many cases already travelling at below their service, or design speeds, it does indicate that there could be a limit to how much slower vessels will travel, even on ballast voyages. Those vessels that are operating in a weak market will also have even less incentive to slow down, with Lindstad noting that traditionally, vessels operating in a strong freight market would speed up on their ballast legs in order to secure more cargoes.
Lindstad’s calculations are backed up by data that shows that vessels are currently travelling at 11-12 knots across the dry bulk and tanker segments, but that even in periods of extreme market weaknes
In addition to this, Lindstad notes that there are other factors that contribute to overall cost of each vessel journey, such as newbuilding costs, Capex, Opex and time charter costs, as well as bunker fuel. Vessels can slow down, saving on their bunker fuel costs, but this means that many of these expenses are higher per voyage, as takes longer for the vessel to reach its destination. For this reason, she calculates that the speed that gives the lowest overall cost per nautical mile for the Supramax would be 12.5 knots, giving it a cost per mile of around USD112/nm. If the vessel were to slow down, the cost per nautical mile would rise significantly – with the costs increasing exponentially the slower the vessel goes. Slowing from 12.5knots to 10 knots would increase the cost by only around USD5/nm, for example, but slowing down a further 2.5 knots from this to 7.5 knots would increase it by USD22.5/nm, from USD115/nm to USD137.5/nm.
This does not mean that vessels will not slow steam on ballast voyages, she notes, but this would reflect ships operating in a weak market deliberately slowing down in order to take capacity out of the market, instead of acting to save fuel. “In reality consumption is also lower in ballast, so it doesn’t make sense to slow steam on the ballast leg to save money. But it does make sense to slow steam to take capacity out of the market. On your loading legs you have your contractual obligations, so to go slowly would be expensive.”
Given that vessels are in many cases already travelling at below their service, or design speeds, it does indicate that there could be a limit to how much slower vessels will travel, even on ballast voyages. Those vessels that are operating in a weak market will also have even less incentive to slow down, with Lindstad noting that traditionally, vessels operating in a strong freight market would speed up on their ballast legs in order to secure more cargoes.
Lindstad’s calculations are backed up by data that shows that vessels are currently travelling at 11-12 knots across the dry bulk and tanker segments, but that even in periods of extreme market weaknes