Is diesel-electric or all-electric the future?

[Na Mara]

Hi all,

An interesting piece of research came out in Sweden today that I thought I would share. Some researchers at Lund university did some life-cycle analysis on cars with different kinds of engine architectures and they found that plugin hybrid cars have lower lifetime emissions than BEV´s even in a country like Sweden, where electricity is essentially CO2 neutral, and even using standard gasoline. The difference between HVO diesel fuelled plugin hybrids and BEV´s was starkly in favour of the HVO diesel fueled plugin hybrids.

Basically, the embodied emissions in the larger battery packs of modern BEV´s is approaching 10 times those in a plugin hybrid´s battery pack. Most of the time the electric range of BEV's greatly exceeds the daily driving range needed and so most of the time you are lugging around a big heavy battery for no benefit while the plugin hybrids battery has been specifically sized to meet 80% of daily driving needs. Thus the plugin will do most of its miles on electric anyway and even when its using diesel HVO has only 10% of the emissions of normal diesel. All together this makes the plugin the more environmental option over a whole lifecycle even when electricity is nearly CO2 free.

I think this is interesting for sailors and motorboaters as it questions the received wisdom that the future of boating is all electric. Think about the embodied emissions of a battery bank substantial enough to give the modern sailboat about 50 nautical miles of range underpower, that will also allow for all electric cooking, water heating, air-conditioning and heating, instrumentation and so on. That bank is going to be in the 50-60Kwh range (similar to modern BEV banks). At 48 volts that is equivalent to 1250 Ah bank, a 2500 Ah bank at 24 V, or a 5000 Ah bank at 12V. Now imagine a diesel electric hybrid capable of maybe 5 nautical miles of electric propulsion whilst running ship systems but that heats water off the engine/generator when it runs, that has a Wallas diesel electric oven and stove or similar, a diesel space heater, and so on. This sailboat is going to maybe have about 8 Kwh of batteries (equivalent to about 170Ah at 48V, 340Ah at 24V or 680Ah at 12V). Both boats will be set up for hydrogeneration underway and both will probably also have additional charging using panels. The difference is that the diesel electric also has a diesel generator and a much smaller battery bank.

Now wont the same argument hold here as for cars. With a 5 nautical mile e-range the diesel electric boat will mostly get itself into and out of marinas using electricity, and with the regenerative charging it will mostly meet onboard needs underway without running the generator. The exception would be heating operations that simply burn the diesel on board as in this mode diesel is almost 100% efficient. If, in addition, the diesel used is HVO or equivalent, then you have a very clean boat with an embodied energy not significantly higher than that of a normal cruiser. A typical 40 ft might have about 400-600Ah at 12V in terms of battery capacity. Now compare that to the all electric boat with its substantially larger bank of batteries that is trying to do everything with electricity and ask yourself, does the latter really make sense?

What of hydrogen I hear you ask. Well the same is true of a hydrogen electric boat. Heating operations with hydrogen are more efficient if you just burn the hydrogen than if you convert it to electricity and then use the electricity to heat stuff. Similarly, a hydrogen feulcell boat is one where the battery bank will be significantly smaller than a BEV and will thereby have a lower embodied emissions cost.

So the question still holds true. Does the all electric boat really make sense for cruising?

I'm genuinely interested in the answer as I am going to re power and redo the galley in the next year or two and I'm either going all electric or diesel electric. At the moment I edging toward diesel electric, but I'm open to counter arguments.

[Emoyeni]

I think a big aspect of this decision depends on your goals of cruising, timelines, locations, etc.

For me personally, I sail in the Great Lakes. if I'm going to go through the trouble of a repower and have electric propulsion, knowing that >95% of the time the electric will be enough, I would prefer space in the boat to keep a generator to rent or buy for a longer voyage. That way 95% of the time I don't have the stink, of diesel and the complexity of a Diesel engine to worry about. To each their own though!

[CarlF]

I'd go even farther. I don't believe that diesel electric makes sense in most cruising applications where there is a single genset.

Unlike a car, a marine diesel can be run 90%+ of the time at exactly its most efficient rpm and there is essentially no energy loss in a modern marine transmission. The power all goes to the spinning shaft.

In a diesel electric the genset is a diesel engine using the same amount of fuel per Kw as the propulsion engine - but then they mess it all up with huge energy losses by converting the diesel rotational energy to electricity with an alternator, then maybe convert the electricity through a charger to battery chemistry through voltage-loss causing wires, and then converting it all back again through a controller and wires to rotational energy in an electric motor to turn the shaft. I believe you lose well over 20% of the energy doing all this compared to a diesel engine directly coupled to a shaft through a transmission to the same shaft.

Large diesel electric ships (or trains) have multiple generators and run just the the number needed for the situation. This obviously saves fuel.

And you don't see diesel electric trucks because there is only one engine. Even hybrid cars are not like diesel electric. The gasoline engine directly drives the wheels through a clutch with little energy loss. The electric motor can also drive the wheels from battery power providing two power sources to the wheels.

It's simply Newtonian physics.

[sailingunity]

I like the concept, but in reality I think the complication of a hybrid electric removes too much from the reliability of the system as a whole. You would have to identify or develop a transmission that could merge both inputs. Don't get me wrong, I'm all for zero emissions, but the majority of diesel and gas emissions is from auto and trucks - and on land they have much less need for such absolute reliability that we have.

If energy density and charging systems become more efficient, I would consider converting to all electric, though there are some drawbacks I would expect overall reliability to increase - and maintenance to decrease!

[Na Mara]

CarlF. The difference on a sailboat is that the engine is the auxiliary mode of propulsion and not the primary. I agree that on a motorboat diesel electric motivation makes little sense over straight diesel. Maybe you could make a case for a parallel hybrid like the Greenline boats but even there the benefits are probably marginal. But on a sail boat your primary motivation is the sails, the engine is ideally just to get you into and out of tight spots at the start and end of the journey. As such the efficiency argument you make is less relevant.

A diesel engine can be up to about 40% efficient in turning the chemical energy in the diesel into kinetic energy in the drive line. Generators and electric motors can operate at up to 80 or 90% efficiency and lithium batteries have charging efficiencies of around 99% so losses in converting diesel to electric potential energy and then back to kinetic energy are of the order of 30% which in effect means that the diesel electric only has about 75% of the efficiency of a standard diesel when powering the boat off of electricity generated aboard. If you were motoring all the time this would be nuts, but on a sailboat you will mostly be sailing and then you will be generating electricity through the same drive line on a diesel electric. Let's imagine that a diesel electric does 1 in every 2 nautical miles at sea on battery charge not acquired through the diesel generator. In that usage profile the diesel electric will use about two thirds of the fuel of the standard auxiliary diesel. Obviously if one is careful in ones cruising with a diesel electric then one can do better than this.

[Na Mara]

An addendum to all this about the drivetrain is of course the current fad for going all electric in boat systems. Electric water heating, space heating, cooking, bilge pumps, etc. This is supposed to make sense on the all electric boat as you have a whopping great big battery bank anyway to power the drives for a reasonable range, so why not go all in. I suppose this is all fine if you are not using diesel to generate electricity for any of this but if you are then surely this too is nuts. As stated previously, turning diesel into electricity you loose about 70% of the energy stored in the diesel. Now you use that to heat your water for a cup of coffee on your induction stove, which is about 90% efficient. So, allowing for inefficiencies in a diesel stove, about 60% of the energy in the diesel has been lost in this process relative to just heating the water directly. That is nuts. The same goes for water and space heating also. So again one wonders whether the supposed benefit of being able to go all electric for ship systems really holds water. Perhaps if you truly have a totally electric boat with no diesel generator that relies solely on renewable generation and shore power, but that doesn't seem realistic given the energy requirements just for heating and cooking never mind all the other systems and motivation.

Again are we, for the sake of some purist fantasy of the all electric boat, actually pursuing an ideal that is in fact more harmful to the environment than an alternative that still involves diesel? Again its an honest question as I too am attracted to the clean simplicity of the all electric sailboat. Its just the article has got me thinking that maybe I'm being sold on something that doesn't pass muster once you really start to think about it.

[silkie]

The basic problem the OP identify seems to be the battery bank.

[Lepke]

I've run a number of diesel electric vessels. You'd need a huge, expensive battery bank. Overall it's not as efficient as direct coupled engines. My guess is you'd spend as much for a small diesel electric conversion as all the fuel used in the lifetime of the average boat.

[danstanford]

I have an Oceanvolt powered boat and for almost all of the situations I encounter the electric motor and batteries plus sailing is perfect. I have 20 nm range and in almost all cases for me that covers the need by a factor of 5 or so.
The addition of a 3000 w generator gives me basically similar range to diesel boats but the consumption of fuel will only happen once a year or so when I am on a long trip with no wind or adverse winds.
The diesel-electric is as close to perfect as it gets at the moment save for the cost factor.

[CarlF]

I think we agree that turning a cruising boat's propeller shaft with a genset is always less efficient than driving that shaft directly coupled to a diesel engine.

What you are advocating - which makes sense - is a dual drive. A diesel engine connected to a shaft and also an electric motor connected to the same shaft where the electric motor uses electricity not created by burning diesel.

When battery power is available from solar panels or propeller regeneration the electric motor would be used. If battery power was not available, the conventional propulsion diesel would be used.

Presumably, such a boat would not have a genset at all as the solar panels and regeneration would be enough for the hotel loads on board.

The only problem with your plan is that the regeneration systems installed on sailboats to date have not provided very much electricity. I have several friends who tried them but found that in actual cruising they are just about useless. They only make sense when the boat is sailing near hull speed such that there is excess sail power available. At lower wind speeds a large regenerating propeller slows the boat down too much.

If you could create an inexpensive and efficient propeller regeneration system that could rapidly charge a large lithium battery bank that would be very exciting.

[Na Mara]

Lepke, Interestingly I just looked into the cost of this.

If I went to Oceanvolt for this system it would cost me 54000 euros ex 25% sales tax for the following system.

Shaftdrive 20

40-60hp equivalent
35nm range on 26.6kwh battery bank
11h shore charging on a 2kw charger
300W hydroregen at 6 kns

To make the boat truly all electric I would also have to add induction cooker and electric space heating plus a 5kw inverter (mainly for the cooker). So all in we are talking nearly 80000 euro to go all electric.

Is such a system viable for long term cruising? Lets say that when cruising you spend one day a week traveling for every 6 at anchor. Lets also imagine that you manage to keep motoring down to 10nm on that trip and that you use your stove for about an hour a day at an average effect of 1,5kw. Add all the other systems in lets say that you daily usage on the hook is 2,5kWh. Over 6 days that is 15 kWh. Now add the 750kWh/nm x 10nm to get you into and out of that anchorage, and you have used 22,5kWh of your 26,6kWh bank. This looks good, there is enough capacity in the battery to get you into and out of the anchorage plus meet your domestic needs.

But now you need to replace all that energy. Lets say that you sail for all of the 7th day at 6kn. Through hydro regen you would replace 7,5kWh. That is enough to cover getting you into and out of the anchorages but not enough to cover your usage in the anchorage. You are going to need to augment the hydrogenation with something else. If you do it with solar then you will need to generate 15kWh of energy every 7 days of insolation on average. That works out as 2.2kWh per day on average. Lets be generous and say that you get effectively 5 hrs of insolation a day on average, then you are going to need about 500W of solar panels to meet these needs given allowances for inefficiencies.

So add 600W of solar to the above system to be on the safe side and you have a workable system. On my boat that would require an arch over the aftdeck plus panels and sundries and fitting. All in we are talking another 10000-15000 euros by the time we are finished. But now you are generating more energy aboard both when stationary and on the move so you can probably get away with a slightly smaller battery pack. Lets say that you judge 20nm of range as sufficient. Then you only need about 15kWh of battery and you have reduced the cost of the system by 10000 euros.

So the all electric sailboat, that is totally independent of shore power, gas and diesel is a practical proposition if you throw about 80000-85000 euros at the problem.

Now consider the diesel electric equivalent that uses gas for cooking.

The spec of such a boat would be:
20kW diesel generator
40-60hp equivalent electric motor
8nm range on 6kWh battery bank
6h shore charging on a 1kw charger
300W hydroregen at 6 kns

The 6kWh bank is 6000 euros and the diesel generator installed is about 18000 euros so together they come to 25000 euros. That is almost precisely the same as the 15kWh plus solar installation of the alternative (maybe 5000 or so cheaper). So no big win here. The costs for the electric engine installation, chargers and so on are also nearly the same. But where the win comes from is the auxiliary systems. You don't need an inverter with this system and you certainly don't need one that is 5kw. You also don't need to replace your diesel electric heater, your belt driven bilge pump, your gas stove, your hot water exchanger, etc, etc. Replacing all of that is maybe 20000 euros all in.

So for me, given where I am starting from, a diesel electric repowering is going to cost about 60000 euros, whereas a full all electric repowering is going to cost at least 80000 euros. That is a big difference on a boat that is only worth maybe 200000 euros to start with.

Finally, going back to where this thread started it is also questionable whether it is worth it environmentally. The diesel electric boat will be doing most of its motoring on electric anyway, and will be generating enough under sail to cover its much lower energy needs when stationary so run time on the generator and thus diesel usage will be minimal (particularly with a couple of solar panels added). Admittedly, one would still be using hydrocarbons for cooking and heating away from harbour (in harbour one can just use portable induction hobs and electric heaters) but the pollution from this and the diesel has to be measured against the embodied emissions in the extra 9kWh of batteries in the all electric boat and the research form Lund suggests that in that calculation the diesel electric will win even using standard fuels, and will win big using HVO and bioLPG.

In summary, the all electric boat gives you complete autonomy and is utterly clean at the point of use and is very low maintenance. However, it is questionable whether it is actually superior to a diesel electric system over its entire life cycle in environmental terms and it is at least a third again as expensive from my starting point as an upgrade over the diesel electric alternative. That alternative also offers benefits in terms of range under power.

But to be honest all these calculations are making wonder whether I should just not bother with the repower. Why not just avoid using the 90hp Yanmar as much as possible, fit sufficient renewables to cover my power needs without relying on the engine, and stick with gas for cooking. Probably the embodied emissions in upgrading to diesel electric over what I have is likely not to be worth it even given the fuel savings, and I could do a really mean power and gas system upgrade for about 20000 euro.

[GordMay]

Originally Posted by Na Mara

Hi all,
An interesting piece of research came out in Sweden today that I thought I would share. Some researchers at Lund university ...

Could you provide a link to [or at least, the title of] that actual research?

[valhalla360]

Originally Posted by Na Mara

CarlF. The difference on a sailboat is that the engine is the auxiliary mode of propulsion and not the primary.

Who told you this?

Go down to the ICW some time. You will find 90%+ motoring along.

If you are talking about folks who day sail out of a single marina, it's largely irrelevant. They might burn 5-10gal of diesel per year. You aren't eliminating any significant amount of fuel burnt.

Once you are talking about coastal cruising where people are getting from A to B:
- BEV requires a ton of batteries and you need to stop in a marina almost every night so you can plug in.
- PIH still needs a substantial battery bank to be a viable alternative. There are some possible things that can be done but to be really useful the electric range is going to have to be upwards of 30-50miles.
- Diesel...just fill and go. If you run out, stop and in 10min you have more.

Keep in mind, while there are a few proponents doing a lot of talking and it gets lot of news, I don't think anyone is expecting BEV to be standard any time in the near future. Cars and boats have wildly different power needs and electric is much more favorable to cars vs displacement boats.

[Na Mara]

https://www.sciencedirect.com/scienc...562?via%3Dihub

This is the actual research article. All the news reports on it are in Swedish.

[valhalla360]

Originally Posted by Na Mara

Lepke, Interestingly I just looked into the cost of this.

If I went to Oceanvolt for this system it would cost me 54000 euros ex 25% sales tax for the following system.

Shaftdrive 20

40-60hp equivalent

40-60hp equivalent is 40-60hp...

Cars are different from slow speed displacement boats. Cars size their motors for acceleration. Displacement boats size based on running at hull speed against a stiff wind. That takes HP not "equivalent" HP.