ask for help in Converting a propulsion system for a tugboat to a fully electric

Hello, my name is Shay and I am a mechanical engineering student at the Technion in Israel. I specialize in the marine engineering major and am doing a final project on the feasibility study of converting the propulsion system of a tugboat-type vessel to a fully electric propulsion system. Today the cruise ship's propulsion system is based on a combustion engine and I need to examine the engineering implications of converting the system to a tram with an energy source based on batteries only with the ability to charge in the port.

Below are the data of the propulsion system as it exists today in the sailing vessel:

GM 12V 71NA diesel engine with a power of 365 horse power at a maximum rotation speed of 1800 rpm.

Model combination

Twindisk MG514 with 4.5:1 gear ratio.

-3blade propeller with a diameter of 1.5 meters, P=850mm, BAR=0.56.


Below are the dimensions of the tug:

Length 15.70 meters

Width 4.38 meters

Draft 1.95 meters

Weight (light ship) 17.8 tons

I am interested in finding a drive system that can deliver 365 horse power or 272 kilowatts and work for 10 hours and after 10 hours of work go into charging. My operating regime is 10% at full power of 272kw. 40% at 1400 rpm. 50% at idle 1000 rpm.

I contacted several companies and they told me that I was exaggerating and that the weight of the batteries would be very large, but I am looking to get together with something that is practical, so even if I have to reduce my working hours or performance, I will be able to accept it. My main goal is to examine the effects of stability in the entire spiral design process.
If anyone has a product and an important insight I would be happy to receive it.

I would appreciate it if you could help me, thank you very much!

 

Welcome to the Forum Shay.

Whereabouts is this tug currently operating - I am guessing in Israel?
You mention her lightship displacement of 17.8 tons - do you know what her fuel capacity is, and what her total deadweight capacity is, including fuel, water, stores etc?

I think your main stumbling block might be the requirement for the tug to work for 10 hours before it is allowed to plug in to shore power to re-charge.

The Norwegians seem to be the leaders in small electrically propelled vessels, especially short hop ferries - here is a good example :
MV Ampere - Wikipedia https://en.wikipedia.org/wiki/MV_Ampere

Note though that while she has 2 x 450 kw electric motors (approx three times what your tug has), they also mention that she has 10 tonnes of batteries, and she only operates for 20 minutes on each crossing before plugging in for 10 minutes to get quickly re-charged.

Try googling 'Norway electric ferries' and many more good links will come up.

 

Welcome Shay.

Is swapping out batteries half way through the 10 hour shift possible?
Shore charging for 5 hours, then swapping the battery with a crane or ro-ro style dolly.
So, two batteries, each capable of 5 hour duty cycle.

Do you have a budget?

 

Let's do some math, this will give us a better understanding of what's required.
(1h x 272kW) + (4h x 200kW) + (5h x 50kW) = 1322kWh + some extra so you don't run the battery down completely. I haven't actually checked how much power a 12V71 makes at 1000 and 1400rpm, so the number could be lower. For simplicity I will postulate a battery of 1500kWh. For the motor and controller we can use off the shelf equipment from the light rail department, the three most used voltages beeing 600, 750 and 1500VDC. The Thunder Sky (Winston) 1000Ah 3.3V LiFePO4 cell is readily available, so I will use it as a base. The options are 455 cells in series for 1500V, or 2P228S for 750V.

One of this 1000Ah cells weighs 41kg, so the complete battery incuding boxes will come in at approx. 19t. The volume of the cell is 0.0259 cum, so the complete battery will be approx. 12 cubic meters.
A different battery chemistry or different cell size will give different weight and volume results for the same capacity.

The above is just an example and a simple one at that. Better data will give you more precise results.
I won't adress the costs because that's its own chapter.

You can also explore the hybrid option, like the E-kotug. E-Kotug tugboat - E-Mobility Engineering https://www.emobility-engineering.com/ekotug-rotortug-powertrain/

 

Hello everyone,
To continuly to our corresponce I re-evaluated and thoroughly examined my design requirements and came to some insights, I would be happy if you could help me find a solution for the following data:

Below are the tug's data:
Length 15.70 meters
Width 4.38 meters
Draft 1.95 meters
Total displacement for the vessel in its current condition and maximum load 38 tons
When the weight of the fuel together with the engine and the accompanying equipment that came out during the conversion is estimated to be at least 10 tons (it is an old vessel with excessive and unnecessary fuel reserves in relation to its mission requirements).

The tug has one propeller and the transmission ratio between the engine and the propeller is 1:4.5

I am interested in finding an electric propulsion system that includes an energy store, engine and the relevant auxiliary assemblies that will be able to work for 8 hours in the following mission profile (and then enter the port for charging):

10% of the time pushing at maximum engine power - 272 kW (engine rotation speed 1800 rpm, propeller rotation speed 400 rpm) at this power in the last bollard pull test, a value of about 3800 kg was measured on a dynamometer.
10% of the time cruising at maximum speed at maximum rotation speed from the engine - 203 kW (engine rotation speed 1800 rpm, propeller rotation speed 400 rpm)
30% of the time cruising at low speed with a medium rotation speed from the engine - 69.5 kW (engine rotation speed 1300 rpm, propeller rotation speed 289 rpm)
50% of the time the engine idles at minimum speed - 13.6 kW (engine speed 1000 rpm)

A total of 600kWh (if it is customary to take acceptable reserves, I would love to know).


In conclusion, I am looking for an electric drive system that includes an energy reserve of 600kWh with the appropriate reserves, an electric motor that will meet the requirements of the task listed and the necessary auxiliary assemblies such as a chopper for switching if required, a control unit, etc. that will come together in the order of 10 tons.

If you have a product that can fit, I would be happy to receive information about it, and if you don't have one, I would love to know the closest product you have so that I can test it. If the product comes close to meeting the requirements, I can reduce and slightly limit the task requirements and use it.
I would appreciate it if you could help me, thank you very much!

 

Hi Shay,
My name is Florian and I just startet to work for High Voltage Battery company. I don't know if I can help you. But the topic interests me because I want to understand requirments for application you describe. So if you would suggest 10 400V batteries with 63kWh and a total weight of about 4.000 kg. Would this match a part of your requirement?
Cheers, Florian

 

@Shay Rhiner , it looks from here like @Rumars did help you. He described a product, did the math, stated the results. There are no products that will perform substantially differently because the limitations aren't the company logo and the ad campaign, they are immutable laws of physics.

 

He needs 600kWh usable energy, the total battery capacity depends on the used cell and the settings you are comfortable with. Most manufacturers don't recommend regular discharges to 0, so you need to add at least 15% for the bottom end, plus something for the top end to accommodate charging strategies. I would say the total capacity needs to be at least 700kWh.

The question for your product is if the 63kWh designation is total (reflects capacity at nominal cell voltage), or commercial (reflects actual useable capacity).

System voltage depends on more then components availability.
400V means that for 272kW at the shaft you need 680A. That's nominal you need to add some conversion losses for the at battery number. First thing to check is if the cells can sustain that level of discharge continuously and if the heat management that's already implemented is sufficient.

For your product the question is if the existing modules can sustain a 4.5-5C discharge for 1h.

On the controller side the question is what's available off the shelf that can deliver 680A+ continuously. For example the Zilla 2K http://www.manzanitamicro.com/produ...duct_id=89&flypage=flypage.tpl&pop=0&vmcchk=1 manufacturer is stating "over 600A at 50°C coolant temperature". This is probably one if not the most powerful controller available on the open market in this voltage range, and to use it one would still need to design a custom sea water/glycol heat exchanger to keep it happy.

This is why I recommended going to a higher voltage, as high as 1500V if possible, it keeps the amps and the associated heat low.
High voltage BMS systems are available, for example REC makes one for up to 800V. BATTERY MANAGEMENT SYSTEM – REC BMS https://www.rec-bms.com/battery-management-system/
Plus of course you can use all the easily available light rail components, wich you can even get second hand.

 

Thank you very much for everyone's comments.

I'll be specific about what I'm missing.
I would love to understand if my engine requirements make sense for an electric engine?
I would love to understand what are the disadvantages of working with high voltage energy storage devices like the one mentioned - 1500V?
And of course I would love to hear what other aspects are important in this conversion that I am performing and why is it also important to pay attention? Mainly around the subject of the transition to an electric motor in front of the fact that it is a tug-type vessel that operates in a mission profile of "free shipping" with resistance only from its own drag and a mission profile of "bollard pull" of pushing at maximum power without movement and at almost zero speed?

I am attaching my current engine graph.

 

It makes sense but don't go making assumptions because of it.

Electrocution and dieing. Fire.

Weight! Prop sizing.

Safety, especially fire.

Bollard pulls are always measured at zero speed.

 

Hi Rumars,

Thank you very much - I really appreciate your effort. This helps me already.

So, yes. I was refering to the nominal capacity. Usable are 56,5 kwh.

I can not deliver 1500V solution, but two batteries in parallel would deliver 800V (nominal) meaning 594 - 812 in reality.

So how would you judge a solution with:

12 packs 2 in parallel 678kWh usable energy and 1370 continous discharge. Weight about 5000 kg.

I also tried to look on even higher voltage but then it is getting difficult with finding components.

Cheers,
Florian

 

You can get electric motors with the required power at the specified range, and if you search even ones that would not need a gearbox. You need to decide what type of motor you want, and subsequently the adjacent controller.
You have a 6-700kWh battery, regardless of voltage such a thing is only as safe as your protocols. Your biggest problem will be finding off the shelf solutions for over 800V.
This is how I see it:
1. You hire yourself some experts to do the entire drivetrain. They can come from a university or research centre, or you can use a commercial firm who deals with battery traction. They will deliver a complete package with an operation manual. As an NA you are only concerned about space and weight distribution, it doesn't matter what secret sauce they use inside the box. After all you're not really interested what kind of injection pump the diesel uses either.
2. You can educate yourself and configure a drivetrain from components that are available off the shelf in the open market. This requires a deep dive in the sales catalogs of different manufacturers to see if they have something that fits your needs, and at what price. To give you a simple example, a 300kW, 400V, 1800rpm asynchronous AC motor isn't hard to find since it's a common industrial product, but the VFD to drive it from batteries isn't. On the other hand, series traction motors wich you can easily get a controller for (see my link to the Zilla 2K) aren't as common anymore at this voltage, but there are plenty of manufacturers willing to wind you one.
Batteries are similar, you can easily buy components for up to 800V, then it becomes scarce.
Another component you need to keep track of is the charger and its associated infrastructure.

For you as a manufacturer it's all about what your existing BMS system can do with the cells you use. You can put 12 packs in parallel at 400V, or you can put 6 parallel x 2 series for 800V, either is fine. For the customer it's irrelevant what you do internally, his requirements don't change, he wants discharge rate X at voltage Y. You are manufacturers, in theory you can reconfigure the pack at cell level if you develop the right BMS.

 

Hello everyone,
I am after a long round of conversations with different companies and shipyards and am unable to find a comprehensive solution. There is a company that deals with electric motors and speed regulators, there is a company that deals with gears, there is a company that deals with batteries and there is a company that deals with voltage converters, but isn't there one integrator that brings them all together? I contacted several shipyards and was told that they had no solution for me.
All in all, I need an electric drive system that will weigh 10-12 tons for all the components and that will be able to provide me with a torque of 6500-7000 Nm for a single axle at 400 rpm.
It is clear to me that in order to meet the weight requirement in the end I will have to cut the capacity of the batteries, but with that I can play contrary to the requirements of the engine and the combination.

If someone can link me to an integrator or share with me such an existing system, I would appreciate it.

 

Hi Shay,
I have on tipp - it is a swizz company that is doing this task for heavy equipment - but not boats. But they are the best I know. Maybe you can contact them and ask if they would "expand" their expertise?

SUNCAR AG
Schlieren,
Schweiz

Cheers,
Florian

 

Thanks, but I'm looking for providers who live in the field because there are a lot of nuances and I need an answer in a relatively short period of time.