In my most recent line of work technological prowess has been a major selling point to lure in our customers, unsurprisingly so given the rate of technological change in the marine industry. Perhaps nowhere has this been more evident than in our adoption of electric propulsion.
This got me thinking, high technology among commercial marine operators is one thing, but what about for the fair weather leisure boat owner; will we soon see everyone at the yacht club silently gliding in and out of the marina propelled by an eco friendly electric motor, or is there still life left in the trusty, if a little environmentally unfriendly, diesel engine?
I believe the time will come when electric drives begin to overtake marine diesels; after all there’s already been a massive uptake in the car industry, and that looks set to keep growing with every passing year; so it isn’t a huge leap of faith to believe the same will one day be true for boats. However I don’t believe that time will be anytime soon, for reasons I shall explain below.
Purely Electric or Diesel Electric?
It’s important to distinguish between 100% electric boats and diesel electric boats, because they are two very different methods of propulsion.
Diesel electric drives are already quite a common sight, benefitting from the advantages of electric thrusters, but making use of an onboard diesel generator to actually make the electricity required to drive the thrusters, and power all the auxiliary systems.
Diesel electric drives have many advantages including:
- Unlike diesel propulsion engines, the generator can be positioned in the most convenient place from a stability point of view; given that it is purely there to generate electricity
- Redundancy in the form of battery power continuing to power the electric drive should the generator fail
- Reduced noise
- Better fuel efficiency due to the output load of the generator being optimised to suit the drive unit(s)
- Comparable endurance to a diesel drive
However, from a carbon footprint point of view diesel electric drives aren’t the ideal solution that a pure electric drive strives to be. Clearly fossil fuel is still burned, and emissions still produced.
Purely electric drives (the Holy Grail of propulsion) use only onboard batteries or renewable energy in the form of wind or solar power to drive a vessel.
Does The Weight of Batteries Make Purely Electric Boats Prohibitive?
With all of the marvels in technological advancement we’ve had over recent years, it’s fair to say that batteries still have a long way to go, and sadly the excessive power to weight ratio inherent with battery power makes it prohibitive in most cases.
Believe it or not electrically driven vehicles aren’t a new idea at all. It didn’t take long after the invention of the lead acid battery in 1859 for the technology to be experimented with in the ‘horseless carriages’ of the day.
In fact it’s fair to say that the earliest developments in gas engines took place more or less concurrently with electrically driven vehicles. Why then have electric vehicles always lagged behind?
Yep, they’re just too damn heavy.
Even with the most cutting edge lithium ion batteries being developed in the car industry, if the weight isn’t quite so much of an issue, the cost almost certainly is.
However we should take solace in the fact this will all improve in the not too distant future. With the car industry busy at work tackling the issues around batteries, it will only be a matter of time before their successes trickle down to the marine sector.
Are Electric Drives Powerful Enough For Boats?
Absolutely, if you look at what is manufactured by a company such as Torqueedo, with their electric outboard and inboard systems, you’ll see it’s possible to get your hands on motors that kick out up to 100kW of power, with upwards of 80 horsepower or more. If you can picture 80 horses you can imagine what sort of payload such a unit could shift!
Again though, delivering the energy required to drive such a unit is a far trickier affair. In simple terms batteries are about 100 times less efficient pound for pound than gasoline or diesel.
In other words the weight of battery required to shift something that demands a 100kW motor (or even something much smaller) would be so large that it would sink the boat.
Are Electric Drives Reliable?
One of the great advantages of electric motors is that they don’t have anything like the same level of demands on them from a wear and tear/maintenance point of view.
In theory an electric motor doesn’t require any upkeep throughout its working life, short of periodically greasing the externally visible drive shaft.
Of course electric drive systems are slightly more complex than just batteries, cabling and a motor. The other critical component is a control box, which is essentially the brain you interface with to get the drive system to behave as per your instructions.
As you can probably imagine this is a complex bit of kit, and though not inherently bound to fail, if it were to, it wouldn’t be easy to fix, especially a long way from your home port.
Are Electric Drives Cheaper to Run Than Diesels?
In terms of purchase cost you’ll find electric drives are considerably more expensive than diesel engines.
For comparison’s sake:
- A Yanmar 3JH5 Inboard Engine 39hp/29.4kW retails for about $10k
- A Torqeedo Deep Blue 25i 1400 40hp/25kW Inboard electric drive (batteries not included) retails for about $23k
However the money you spend up front is recouped over time with improved fuel economy (if you’re going down the diesel-electric route). If you’re not, then be prepared to fork out a similarly eye watering sum for the batteries.
Can Electricity Be Generated Whilst Under Sail?
One way to get round the issue of lugging around ridiculously heavy banks of batteries on a sailing yacht is to take advantage of the wind and use the movement of your boat through the water to drive the propellers, effectively turning the electric motor into a generator. In turn this would charge up a bank of batteries, giving you enough power to periodically move under power of the electric drive.
In theory you would never/seldom need to charge up from the mains or otherwise, the wind would do all the work, but again, in the near future it would only be viable for short journeys.
Sounds ideal right?
Well yes, but perhaps because it’s too good to be true. At present I’m not aware of any company who have successfully overcome the engineering challenges involved, not only in being able to efficiently generate a useful amount of charge to be used for propulsion purposes (auxiliary systems typically powered by ‘house batteries’ might be a different story), but also to make the same motor equally as effective in ‘drive’ as in ‘power generate’ mode.
A Question of Speed
Knowing that batteries are a fairly prohibitive power source, particularly at speed, there is particular interest about using electric boats in low speed applications when electric drives running at a low speed (4-5 knots) are useful.
What springs to mind would be dawdling in and out of a harbour, where the speed limit is low anyway, with the added benefit of generating no pollution in an area of heavy traffic (and foot fall)
Wind and Solar Power
If batteries are the achilles heal of electric boats, then renewable sources of power generation could well be their saviour.
Solar power in particular lends itself well to boats, with large otherwise unoccupied deck surfaces that can be taken up with solar panels, or alternativelyelevated solar arrays doubling as shades or bivvies.
Again, most real world examples of vessels that run, at least partly, on solar panels tend to run slowly, but who knows where the technology will go.
Will sailing yachts one day have photovoltaic sails?
Now that would be something!
