Tug of War - Electric vs Diesel

[valhalla360]

Originally Posted by skipmac

Rare but over the years I have had a few occasions when I needed all the power I had to avoid a problem docking.

The most recent, I came into a marina for fuel where I had never been before. Approaching into the fuel dock I discovered a current almost 3 kts pushing me into an 80' sailboat with a beautiful, perfect, Awlgrip paint job. If I had been equipped with an underpowered engine I would certainly have ended up crunching the side of that boat.

I've seen similar maneuvers and a few times where a panicky captain gave it full throttle. What would have been a little bump turned into significant damage because now the boat developed significant momentum too quickly as the captain couldn't keep up with everything happening.

I'm not saying you couldn't come across a situation where it might save you but more often I've seen bad things happen when too much power is used docking.

Also, I wasn't suggesting an underpowered boat. The electric enthusiasts were. I've been caught a few times fighting a strong current where it was all the engine could do to make headway against a current. If I cut my HP in 1/2, I would have been losing ground.

[tp12]

I don't believe the EP enthusiasts are suggesting under powering a boat. My understanding is that they're saying that you don't need the same horsepower rating on the electric engine as the diesel to power the boat. This being due to the different characteristics of electric V diesel engines.

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[Muckle Flugga]

Originally Posted by EWOL Props

Don't want to start any new polemic here, so please take it softly, but look at where these guys have arrived with an 1978 boat transformed all electric. They started 1 year ago and are completing the World tour in coming months.
Isn't this the proof that it works ?

Notre position | Eco Sailing Project

For more infos on this specific project:

Eco Sailing Project | Le tour du monde écologique à la voile

We have other working examples...if you have an interest

Well, it may work, but it is still in infancy wrt sailing vessels. I am aware of a VERY expensive large, brand new vessel whose owner is being forced to completely remove the diesel electric system and replace with conventional diesel, as the hybrid system was such a total failure. Couplings failed due to excessive torque, electric motors overheated, systems wouldn't "talk" to each other adequately, and many other such failures. The entire system was a disaster, and this was not a "one off" build, but one of a series from a sexy designer/build firm. I have not sought permission to discuss from the owner or designer so I cannot say more at present, but suffice to say that the build took more than two years, and the owners dream of circumnavigation is now a long way off again, after several emergencies in less than 2000 miles.

That said, diesel electric submarines have been effective since the days of Willenbrock and Buchheim!

[valhalla360]

Originally Posted by tp12

I don't believe the EP enthusiasts are suggesting under powering a boat. My understanding is that they're saying that you don't need the same horsepower rating on the electric engine as the diesel to power the boat. This being due to the different characteristics of electric V diesel engines.

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That's why I made the comment about under powering.

You do need the same HP to get the same performance. A hybrid that can pull extra juice from a battery pack for 10-20 seconds works great for acceleration but no one is bragging about 0 to 6kt times. If you are fighting a 30kt head wind bashing thru 4-6'ers, the diesel is up in it's power band and HP is HP. If you put a 20hp electric up against a 40hp diesel, all else being equal, the diesel wins.

I was challenging the false idea that electric HP was different from gas or diesel HP.

[valhalla360]

Originally Posted by Muckle Flugga

And yet the tug of war between Alecto and Rattler sealed the fate of the paddle steamers…

The efficiency, power and rough water capability or propellers sealed the fate of paddle steamers.

The tug of war was a curiosity.

[tp12]

Originally Posted by valhalla360

That's why I made the comment about under powering.

You do need the same HP to get the same performance. A hybrid that can pull extra juice from a battery pack for 10-20 seconds works great for acceleration but no one is bragging about 0 to 6kt times. If you are fighting a 30kt head wind bashing thru 4-6'ers, the diesel is up in it's power band and HP is HP. If you put a 20hp electric up against a 40hp diesel, all else being equal, the diesel wins.

I was challenging the false idea that electric HP was different from gas or diesel HP.

I think the fact that you get 100% torque at zero rpm and you don't get that from a diesel proves that it's stump pulling power is greater through the Rev range (more area under the curve), for the same overall peak. I used to race motorbikes and when we were tuning I'd always sacrifice a few ponies to make sure I had strong torque from the middle of the range because it's quicker around the track. Horsepower is great for selling bikes but it's torque that wins races. It's torque that gets you up the hill, off the line or around the dock.

I don't profess to be an expert but it seems to me that a good battery bank, charging capability and a dc generator would also cover the longer range scenarios.

It's been explained before on here how the different characteristics of electric and diesel engines mean you don't need the same peak hp rating. But I'll assume you've read that and disagree.

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[Muckle Flugga]

Originally Posted by valhalla360

The efficiency, power and rough water capability or propellers sealed the fate of paddle steamers.

The tug of war was a curiosity.

Of course that's true, but there's nothing like a good show to secure a propaganda victory. Just like Edison and his electric chair.

[valhalla360]

Originally Posted by tp12

I think the fact that you get 100% torque at zero rpm and you don't get that from a diesel proves that it's stump pulling power is greater through the Rev range (more area under the curve), for the same overall peak. I used to race motorbikes and when we were tuning I'd always sacrifice a few ponies to make sure I had strong torque from the middle of the range because it's quicker around the track. Horsepower is great for selling bikes but it's torque that wins races. It's torque that gets you up the hill, off the line or around the dock.

I don't profess to be an expert but it seems to me that a good battery bank, charging capability and a dc generator would also cover the longer range scenarios.

It's been explained before on here how the different characteristics of electric and diesel engines mean you don't need the same peak hp rating. But I'll assume you've read that and disagree.

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You are explaining what I keep saying:

Off the line, that instant torque will win out BUT for outfitting a cruising boat, no one cares about off the line power. No one talks about 0 to 6 kt times for cruising boats.

Racing motorcycles around a track is all about acceleration and braking. You might only be doing 10mph thru a hairpin curve then need to get it up to 40-50mph in 200yds while climbing a hill. Then you let off the gas to go thru another tight turn before accelerating again.

On a cruising boat, you typically push the throttle up to cruising speed and in 20-40 seconds you hit 6kts and that's where you leave it for the next few hours. Peak power in cruising boats is typically, used at speed when fighting strong currents or head winds. In that scenario, the diesel/gas engine is able to get up into it's peak output range and there is no magical difference with electric HP vs diesel HP in that scenario.

[dlymn]

Engine characteristics include Horsepower and torque. A combustion motor can be designed to have high torque and low horsepower or low torque and high horsepower. Torque determines how fast you can accelerate, horsepower determines top speed. They are not interchangeable.

Furthermore a kilowatt is a kilowatt and is a metric measure of horsepower. A 10kw electric motor has the same potential power as a 10 kw diesel engine and so will drive the boat to the same top speed all things considered. It's just that the electric motor will get to that speed faster.

Combustion motors have a narrow rpm range where they produce maximum power and electrics produce maximum power over a wide range of rpm. If gearing is such that a combustion motor finds it difficult to achieve BMEP (the revs where maximum power is produced), it won't hit top speed.

[med]

How big a battery bank do I need to replace the equivalent of 150 gallons of diesel?

And how much does that battery bank cost?

[StuM]

Originally Posted by dlymn

Engine characteristics include Horsepower and torque. A combustion motor can be designed to have high torque and low horsepower or low torque and high horsepower. Torque determines how fast you can accelerate, horsepower determines top speed. They are not interchangeable.

Furthermore a kilowatt is a kilowatt and is a metric measure of horsepower. A 10kw electric motor has the same potential power as a 10 kw diesel engine and so will drive the boat to the same top speed all things considered. It's just that the electric motor will get to that speed faster.

Combustion motors have a narrow rpm range where they produce maximum power and electrics produce maximum power over a wide range of rpm. If gearing is such that a combustion motor finds it difficult to achieve BMEP (the revs where maximum power is produced), it won't hit top speed.

Very clearly explained.

[dlymn]

A 12v x 200 A/H battery stores 2.4kwatts, but you should only drain to 60% of capacity and so each battery is capable of providing about 1kw of energy for one hour. If you boat needs 30 kWh to propel it at cruising speeds, this suggests you might need 30 batteries. Let's be really optimistic and reduce this by a factor of ten. Let's dream that you only need 3 batteries to cruise for one hour.

My boat uses 4 litres/hour and so I can cruise for abou 40 hours on 150 litres. To do the same with batteries without recharge might require at least 120 batteries. The real usage might actually boost this to anything up to1200 batteries

The way to do this is to have a diesel generator with a small bank of batteries driving an electric propulsion system. You need a 30kw generator to charge the batteries at the same rate of consumption if you're using that much energy to drive the boat. A smallergenerator means you've got the motor running all night. This diesel electric system basically means that you have added more batteries and an electric motor into the drive system and your only benefit is that you can beat the other boats the same size at the lights

[Pitchondesign]

Most of the electric motors are either 48v or 72v. No problem putting 12v batteries in series to get the right voltage. Also no problem getting 48v or 72v chargers that run off 110v and 220v. (BTW: a 100amp 72v charger is big and expensive). So using a generator or shore power to charge the batteries makes sense. If the only charging source is solar or wind there is a problem. There are no solar controllers that I'm aware of that output 48v. or 72v. So how do you use solar or wind for charging? It would seem that you would need a separate 12v battery bank which would then run through an inverter, which would then run to the 48v or 72v charger. If this were the case, the transmission and conversion losses start to add up, as well as the cost and complexity. Starts to make a straight diesel propulsion system look simple.

[tp12]

Originally Posted by valhalla360

You are explaining what I keep saying:

I think there are subtle differences.

Originally Posted by valhalla360

Off the line, that instant torque will win out BUT for outfitting a cruising boat, no one cares about off the line power. No one talks about 0 to 6 kt times for cruising boats.

For manoeuvering around the dock when the wind comes up, I think you do care about torque delivery. With the electric engine you also get very fine control over the engine that you don't get with the diesel. I would imagine the diesel would feel like it has big turbo lag after getting used to the delivery of the electric engine. Can anyone with experience comment?

Also, it's torque that punches you through waves and fights against the current etc. I think where we differ is the value we place on that torque and where we think it is beneficial.

Originally Posted by valhalla360

On a cruising boat, you typically push the throttle up to cruising speed and in 20-40 seconds you hit 6kts and that's where you leave it for the next few hours. Peak power in cruising boats is typically, used at speed when fighting strong currents or head winds. In that scenario, the diesel/gas engine is able to get up into it's peak output range and there is no magical difference with electric HP vs diesel HP in that scenario.

At peak output, there's no difference. I agree. That's never been my point, however. With the higher torque levels available with the electric engine through the range I'm wondering if you'll need peak power as often. My thinking, and again I'm no expert, is that the extra torque means you're moving the boat more at the lower revs than you are with the diesel, all other things being equal.

It's the application I'm really discussing.

I'd love to see the power and torque curves on some sample motors we could compare ... in the absence of data on cruising applications to compare .... In my mind I've built some AMAZING racebike engines (hahaha) so I find the subject matter interesting. Also because I can see a potential application in my future on a new build cat.

[Terra Nova]

tp--none of your argument is valid to lead one to choose EP. At low rpm, very little torque is required; the propeller easily slips through the water. Torque is required precisely where a diesel provides it.