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

Of course there are people offering turnkey solutions with warranty, you just have to pay for it. For example:
Full electric vessels - Wärtsilä https://www.wartsila.com/marine/products/ship-electrification-solutions/full-electric-vessels
Electric ship propulsion | innovative ship drives https://www.baumueller.com/en/industries/shipbuilding/electric-ship-propulsion

 

GENERAL METHOD TO DETERMINE MOTOR POWER REQUIREMENT FOR A DISPLACEMENT HULL



This method does not cover special hull shapes, cat- or tri-marans or hydrofoil systems.


DRAG
Drag = water pressure (P) on the wetted surface area (A) of the hull, multiplied by the drag coefficient (CD). CD is a measure of the streamlining of the boat hull compared to a flat, blunt shape, and tells us how easily the boat slips through the water.


D = P A CD

Water pressure (P) is the force in pounds on an area of 1 sq. foot caused by water with a mass density (r), calculated by dividing the density of water (w = 62.4 lb/cu ft) by the acceleration of gravity (g = 32.2 ft/sec/sec):


P = ½ r V2 = ½(62.4/32.2) V2 = 0.97 V2, where V = boat speed in feet/second


Note: r is the Greek letter “rho”.


Try to obtain CD from the boat dealer or a marine architect. If CD is unknown, you may figure that most modern hulls have a drag coefficient of about CD = 0.0022 and start with that number.


POWER
Propeller power to move the boat is found using Drag (D) in pounds of force and required speed (V) in feet per second. Remember the required power to move the boat increases if the boat has to run against flow in rivers and streams or against running tides, or if it sails in choppy waters:


Horsepower (HP) = Drag (D) in pounds X Velocity (V) in feet/second

= (XXXXX foot–pounds / second) / (550 ft-lb/sec). This is an approximation and water conditions and exact hull shape will have a significant effect on boat speed.


Total engine power is a function of propeller efficiency and required boat speed.

For example, if the hull requires 10 HP and the prop is 90% efficient at the required speed, then the total required motor power is 10 /.90 = 11.1 HP. Engine or motor performance curves are used to determine RPM at the required power and required speed.


Prop diameter and pitch are selected to allow motor run at the calculated power (motor RPM and torque). Prop pitch is the forward travel distance of the boat per propeller revolution and is chosen to given the required hull speed at the engine/motor RPM. A good, knowledgeable boat or “prop shop” person can help choose the right prop when given the motor horsepower and the required boat speed. After installation, monitor boat speed, motor current and RPM, and adjust prop size if required. If boat speed is too low increase prop pitch. If motor speed is too low and current is high, reduce prop pitch.

©Myron Boyajian

Warfield Electric Co., Inc.

This method may be freely copied or used when author and company are cited.

 

I can’t offer calculations. I am curious as to why a hybrid option would not be best. The diesels are used as both power when needed for the forces to push vessels and charging. The banks are then charged for vessel running without pushing and the boat uses less diesel in the electric mode, and the batteries are fewer and diesel stores fewer. The best part of such a solution is discharged batteries do not disable the vessel.

 

Hey,
The project deals with the conversion of a propulsion system to a fully electric one with the aim of making the cruise ship green in the port environment and to prevent sea pollution in the home port. There is no question at all about whether the system will be hybrid, it is not an option.

 

I mean you no disrespect. @Rumars shed some light on this earlier, but the discussion veered away. The problem with lithium vs diesel is energy density. The energy density of diesel is 50-100 times that of lithium batteries. So, 100kg of diesel fuel is comparable to 5000kg of battery. Rumars suggested 19t of battery ? on a napkin sketch from a different way of looking at it. But the vessel cannot be the same as a typical tug then because the displacement will need to be much greater. If you want an all electric tug; first thing to do is determine how big it’ll need to be versus a diesel tug.

Perhaps it is possible, but electric is not plug n play. The entire concept of a tug would require redesign. I’m guessing on the order of 2-3 times larger. Just use my remarks as a conversation starter. I apologize, I cannot tell you details on tug displacement. However, I would tend to believe tugs are built with very little reserve, so your first challenge is to determine how the vessel must change.

https://transportgeography.org/cont...ation-and-energy/combustibles-energy-content/

 

Hi fallguy, thanks for your interest and involvement. As I wrote in previous messages, there is no problem of space and weight - I will explain it.
This is an old tugboat that was put in unnecessary fuel reserves of about 9000 liters of diesel. That means about 8000 kg of the weight of the fuel is freed up.
The goal right now is to turn it into a ship that works 6 hours a day and goes in for charging at night. If I take 1000kWh according to a number of products I have already seen on the market, I can converge to 6000 kg for the weight of the batteries for this capacity.

Therefore in this specific case there is no need to re-model.

 

good news .. I am sorry if I missed that from earlier comments

 

Highly doubtful. I suspect the fuel is exactly what is needed in case of an exceptional circumstance. Tugs are expected to be versatile - they respond to emergencies and fight fires and do all manner of support jobs around the port. It's very hard to get contracts or make money with a one-trick pony.

Purely as an engineering exercise, your project will require plenty of research and trade-offs and critical thinking. But as a real project, a tug that can can only run for an hour at full throttle seems totally worthless to me. During storms, they have been run for days just helping ships with station keeping at anchor or even tied up. I'd expect a fuel capacity of 2000 to 3000 gallons and the ability to run for 5 days at near full throttle. Check on the contract specification for the port that contracts the tugs. And look at how tugs are shifted around to different ports seasonally and to support the maintenance program of the fleet's operator. Some jobs can get by with a 10% margin of reserves (not many - launch to orbit maybe) but others require a factor of 100. Not 100%, 100.

From an educational standpoint, I think it would be more informative to look at what it would take to duplicate the original propulsions system's power and energy storage. Then make an honest assessment of what you must sacrifice in order to make the conversion practical. Just waving your hands and saying that all that reserve fuel capacity is a waste of space and has no value is not what engineers do. It does have a value, and you need to analyze what that value really is.