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Old 13-12-2015, 19:31   #106
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Re: Tug of War - Electric vs Diesel

diesel power/toque then electric power/torque





These are two engines with different power ratings. You really can only talk about the approximate similarities and differences in the nature of the curves
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Old 13-12-2015, 19:37   #107
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Re: Tug of War - Electric vs Diesel

I don't see how this is relevant in any way. A mistake by a panicked skipper could happen with any kind of power.

Bottom line, there are occasions when a competent skipper, acting appropriately, might avoid a problem or save a bad situation with judicious use of max power. And times when a lack of power could be a problem.

The whole point I was trying to make, most of the marine electric systems available are fairly low power and in my opinion, suitable for small boats. The few that have enough power to move a 40' + boat are very expensive.


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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.
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Old 13-12-2015, 19:40   #108
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Re: Tug of War - Electric vs Diesel

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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?
More batteries than your boat could hold. Depending on the battery chemistry 5-10,000 lbs worth and thousands of dollars.
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Old 13-12-2015, 20:42   #109
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Re: Tug of War - Electric vs Diesel

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I don't see how this is relevant in any way. A mistake by a panicked skipper could happen with any kind of power.

Bottom line, there are occasions when a competent skipper, acting appropriately, might avoid a problem or save a bad situation with judicious use of max power. And times when a lack of power could be a problem.

The whole point I was trying to make, most of the marine electric systems available are fairly low power and in my opinion, suitable for small boats. The few that have enough power to move a 40' + boat are very expensive.
I've never used full throttle while docking and we stay at marinas most of the time but I've seen captains goose the throttle on power boats (arguably overpowered for docking) and it can get ugly very quick. Where as with less power, you have more time to react if you give it a little extra throttle. As I stated before, you could theoretically find a situation where extra power could be helpful but more often than not, I've seen it cause problems.

I believe the small HP suggested is a marketing attempt to make electric look more viable.

They know if they replace a 40hp diesel with a 40hp electric and then put in a battery bank to accommodate it....the price will be thru the roof.

By suggesting an underpowered electric motor, they can claim lower consumption at 1/2 throttle even though to achieve the same speed, the power consumption will be almost identical and the battery bank the same. There is no free ride.
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Old 13-12-2015, 20:51   #110
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Re: Tug of War - Electric vs Diesel

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I think there are subtle differences.

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?

I've never used full throttle around the dock. I have fine control...at least as much as I can tell the difference. I don't have a turbo but if you are counting on the 1/2 second of turbo lag, you already messed up your approach.

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.

And the diesel is putting out it's ideal torque at that point, so the electric motor has no advantage. Though I would challenge you to explain the physics of how torque helps you fight a current (torque could be argued to have a minor effect bashing thru waves)

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.

When it comes time to use full HP to fight wind or current...you are exactly in that range where there is no difference. Revs at the engine doesn't matter, HP = torque * revs. If you want more torque at the prop, you put in a reduction gear.

It's the application I'm really discussing.

That is exactly what I am talking about. If you regularly do tug of war or 0-6kt races, the torque will allow you to use a lower HP motor and come out ahead. In real world application, that low RPM torque is never called on.

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.
Again, race bikes are constantly accelerating and decelerating. It's an application where you rarely reach full HP but are frequently asking for that low end torque to get the bike accelerating.
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Old 13-12-2015, 20:58   #111
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Re: Tug of War - Electric vs Diesel

Well, I respectfully disagree. I can see the value in the ep torque curve. I can see some practical and not so practical applications for it and I'll continue looking into it, especially as technology improves along with more take up.

I'll keep following this discussion too.

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Old 13-12-2015, 21:31   #112
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Re: Tug of War - Electric vs Diesel

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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?
A small thermonuclear reactor might do it...
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Old 14-12-2015, 03:38   #113
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Re: Tug of War - Electric vs Diesel

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Well, I respectfully disagree. I can see the value in the ep torque curve. I can see some practical and not so practical applications for it and I'll continue looking into it, especially as technology improves along with more take up.

I'll keep following this discussion too.

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I can respect that.

If someone wants to buy an electric power train, I have no objection.
If someone asks advice on the pros and cons, I will share the my thoughts.

Please share what you think the advantage are. I might have missed something.
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Old 15-12-2015, 23:45   #114
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Re: Tug of War - Electric vs Diesel

OK, back to the OP for a second re the tug of war test. FWIW I can confirm after speaking with those involved that the electric was used to position the boats, to align them at the beginning and that accounted for the boats moving slightly left at the beginning of the video, and then both boats went to full throttle at same time. So the fact is the electric at approx. half the HP pulled a diesel ICE boat at twice the HP.

A real cruising example of a serial diesel hybrid electric propulsion cat that has been using electric without incident for about a year coastal cruising off east coast Australia is as follows:
44 foot cat with 2x 4kW electric Torqeedo, 10kW LiFePO4 bank and 5kW Eniquest DC genset.

He can motor continuously at 5.5 knots on the generator burning 1 litre/hour and not run down the battery bank at all and still run his house loads. So this is a balanced system for his continuous motoring.

Or he can back off on the speed a bit when becalmed to 4.5 knots and his generator will cycle on and off automatically with about an hour on, an hour off. He is delighted with the performance, although I would agree that his system is under powered for adverse conditions.

If you size your electric motors and propulsion battery bank for adverse conditions (that's what I'm doing) then you need to also aim for a balanced system for continuous motoring and pay careful attention to motor efficiency and charging capacity from the DC genset. It looks very achieveable, and I will let you know how it goes.

The 5 year total cost of ownership also comes out ahead for electric, at least here in Oz with Oz diesel engine pricing, cost of diesel and service/maintenance. If you have a decent solar installation and use regeneration while sailing, EP and a virtually (or actually) 100% electric boat becomes an attractive proposition from many aspects.
No Maintenance. Superior MTBF engines. Quiet motoring. Great motor sailing/improved upwind pointing for cats. No fumes in the cockpit. Great docking control. Less weight. Better cruising Return on Investment (ROI) and Total Cost of Ownership (TCO) after 5 years.

I gotta ask, what's not to like?
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Old 16-12-2015, 00:25   #115
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Re: Tug of War - Electric vs Diesel

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Originally Posted by BigBeakie View Post
OK, back to the OP for a second re the tug of war test. FWIW I can confirm after speaking with those involved that the electric was used to position the boats, to align them at the beginning and that accounted for the boats moving slightly left at the beginning of the video, and then both boats went to full throttle at same time. So the fact is the electric at approx. half the HP pulled a diesel ICE boat at twice the HP.

A real cruising example of a serial diesel hybrid electric propulsion cat that has been using electric without incident for about a year coastal cruising off east coast Australia is as follows:
44 foot cat with 2x 4kW electric Torqeedo, 10kW LiFePO4 bank and 5kW Eniquest DC genset.

He can motor continuously at 5.5 knots on the generator burning 1 litre/hour and not run down the battery bank at all and still run his house loads. So this is a balanced system for his continuous motoring.

Or he can back off on the speed a bit when becalmed to 4.5 knots and his generator will cycle on and off automatically with about an hour on, an hour off. He is delighted with the performance, although I would agree that his system is under powered for adverse conditions.

If you size your electric motors and propulsion battery bank for adverse conditions (that's what I'm doing) then you need to also aim for a balanced system for continuous motoring and pay careful attention to motor efficiency and charging capacity from the DC genset. It looks very achieveable, and I will let you know how it goes.

The 5 year total cost of ownership also comes out ahead for electric, at least here in Oz with Oz diesel engine pricing, cost of diesel and service/maintenance. If you have a decent solar installation and use regeneration while sailing, EP and a virtually (or actually) 100% electric boat becomes an attractive proposition from many aspects.
No Maintenance. Superior MTBF engines. Quiet motoring. Great motor sailing/improved upwind pointing for cats. No fumes in the cockpit. Great docking control. Less weight. Better cruising Return on Investment (ROI) and Total Cost of Ownership (TCO) after 5 years.

I gotta ask, what's not to like?
What do you mean by TCO after five years ?
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Old 16-12-2015, 01:33   #116
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Re: Tug of War - Electric vs Diesel

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He can motor continuously at 5.5 knots on the generator burning 1 litre/hour and not run down the battery bank at all and still run his house loads. So this is a balanced system for his continuous motoring.
So he is using 5HP from his generator.
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Old 16-12-2015, 02:13   #117
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Re: Tug of War - Electric vs Diesel

TCO being all costs over 5 years, the initial capital investment to put the system in, plus all the on costs to run it, maintain it, service it. Depending on how many hours per year you run the engines (therefore how much diesel you use), there will come a break even point when electric propulsion will become cheaper to run than diesel engines.

In the tropics where we will do alot of cruising, there will be a great deal of calm conditions and we expect to motor more than "average", so our crossover break even point will come sooner than someone with low engine hours. We will also be trolling for sport fishing so that would increase engine hours as well.

For us, EP makes a lot of sense. The trick is to put together a well designed and efficient system.

As they say, we didn't make it out of the stone age because we ran out of stones
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Old 16-12-2015, 02:47   #118
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Re: Tug of War - Electric vs Diesel

So conveniently, they were "aligning" the boats and it just happened to create a significant momentum advantage for the system they are pushing.

As far as the other example, you have a boat that appears to be limited to 5.5kts when comparable diesel boats should be able to easily cruise at 8-9kts for extended periods of time. Of course, you can drop back to 5.5kts and get similar efficiency with a diesel powertrain.

What type of diesel generator does he have that requires no maintenance? I'm sure people would love to take the engine and use it for direct power drive.
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Old 16-12-2015, 03:14   #119
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Re: Tug of War - Electric vs Diesel

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TCO being all costs over 5 years, the initial capital investment to put the system in, plus all the on costs to run it, maintain it, service it. Depending on how many hours per year you run the engines (therefore how much diesel you use), there will come a break even point when electric propulsion will become cheaper to run than diesel engines.

In the tropics where we will do alot of cruising, there will be a great deal of calm conditions and we expect to motor more than "average", so our crossover break even point will come sooner than someone with low engine hours. We will also be trolling for sport fishing so that would increase engine hours as well.

For us, EP makes a lot of sense. The trick is to put together a well designed and efficient system.

As they say, we didn't make it out of the stone age because we ran out of stones
From a TCO perspective hanging a 5HP outboard off the back end will be cheaper.
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Old 16-12-2015, 08:30   #120
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Re: Tug of War - Electric vs Diesel

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So conveniently, they were "aligning" the boats and it just happened to create a significant momentum advantage for the system they are pushing.

As far as the other example, you have a boat that appears to be limited to 5.5kts when comparable diesel boats should be able to easily cruise at 8-9kts for extended periods of time. Of course, you can drop back to 5.5kts and get similar efficiency with a diesel powertrain.

What type of diesel generator does he have that requires no maintenance? I'm sure people would love to take the engine and use it for direct power drive.
It is easy to overlook facts when your main objective is to rationalize a radical departure from what makes sense to nearly everyone else.
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