The electric tugboat is one item that is expected to catch the eye of visitors at the International Tug and Salvage Conference (ITS 2010) this week in Vancouver. There, all types from the tugboat world will get a first hand look at the new Bratt tug boat, a tugboat that is equipped with the latest lithium-ion battery technology from Corvus Energy.
That boat design is just the beginning of a new line of tugboats that are expected to be shipping in 2011. In 2011, Corvus Energy and Robert Allan Ltd. Naval Architects, both of Vancouver, as well as Adrenaline Marine Ltd of Delta British Columbia, are to deliver a hybrid diesel-electric tugboat and an all-electric tugboat to Western Maritime Institute. Western Maritime will use the tug boat, a 7.8 meter long boat with 450 horsepower pulling power, to train future tug boat captains.
Naturally, everyone’s excited about the prospects of an all-electric tugboat with the ability to pull heavy cargo ships. And of course there are others that are skeptical that an electric tugboat will outmuscle a diesel tugboat.
One technology that allows tugboats to go electric is the Nickel Manganese Cobalt (NMC) Lithium batteries that Corvus Energy has developed. These new batteries are not only far ahead of lead acid batteries but also way ahead of standard lithium iron phosphate batteries. The NMC batteries offer about 22 percent more power than lithium iron phosphate batteries and 76 percent more power than your typical lead acid battery.
In a paper presented at the conference by Brent Perry, George Roddan and Neil Simmonds, this trio of Corvus battery experts spelled out the power advantages of their NMC batteries in terms of energy density. For NMC batteries, the authors peg the energy density at 163 watt-hours per kilogram compared to a lithium iron phosphate, rating of 129 watt-hours per kilogram. Besides putting lithium iron in a distant second place, NMC puts sodium chloride and lead acid in the dust; sodium nickel chloride, comes in at third with 100 watt-hours per kilogram, and lead acid batteries come in dead last at 20 watt-hours per kilogram.
Besides power and weight advantages, the Corvus’ NMC battery trumps all other contenders in a number of other areas. One of these other winning specifications is self-discharge. Self-discharge, the process by which a battery loses energy when not in use, has always been a problem with lead acid batteries. And that’s because a lead acid battery will lose 4 percent of its power every month regardless of whether or not it’s ever turned on. On the other hand the NMC battery loses only 0.001 percent per month, about 40,000 times less.
With such a low energy density rating and the other problems associated with lead acid batteries you have to wonder why anyone would even consider them. However one reason is as simple as money. Lead acid batteries are less expensive on a unit basis; fitting into budgets of those that are penny wise and pound-foolish, or just plain financially strapped.
However, for those that are long on return on investment, such as tugboat companies, the pennies they save on lead acid batteries are outnumbered by the dollars they lose from excess weight and excess space. Add to this the better reliability of lithium ion batteries, and it’s easy to see why diesel powered tug boat owners are trading in their lead acid batteries for lithium ion.
Although the first electric tugboats will only be used for training, future electric tugboats are aiming at pulling full megaton cargo ships. According to Corvus there are about 2,000 coastal workboats in the world that are more than 40 years old. And of those it estimates that about 450 will be replaced in the next five years and the remaining will be replaced over the next 10 years.
One of the main reasons that tug boat companies are expected to switch from diesel to electric is that that the switch will save about 70 percent on fuel costs, which is expected to translate to a two year return on investment. Another reason is a 60 percent reduction on emissions over diesel, which is something that tugboats will need to meet future emission regulations.
