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Old 07-12-2015, 18:59   #1
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Tug of War - Electric vs Diesel



The video shows a pulling match between 2 equivalent cats, one with 2x 10kW OceanVolts and the other with 29HP diesels.

Assuming this was done legitimately, ie that both boats had full throttle on, this shows the torque advantage of electric motors vs diesel.

Discussion?
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Old 07-12-2015, 19:40   #2
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Re: Tug of War - Electric vs Diesel

Not sure how relevant that is, unless you are operating a tugboat.
A diesel or gasoline engine needs revs to reach maximum torque, electric has max torque at stall.
Unless the electric boat has a generator, after a while the batteries will be exhausted, and the diesel boat will take over.
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Old 07-12-2015, 19:51   #3
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Re: Tug of War - Electric vs Diesel

Slow internet so I can't watch it now but... Were both boats propped for max static thrust using propellers of the same diameter? Was a generator running on the electric boat?
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Old 07-12-2015, 20:13   #4
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Re: Tug of War - Electric vs Diesel

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Originally Posted by ggray View Post
Not sure how relevant that is, unless you are operating a tugboat.
A diesel or gasoline engine needs revs to reach maximum torque, electric has max torque at stall.
Unless the electric boat has a generator, after a while the batteries will be exhausted, and the diesel boat will take over.
Exactly. Torque, pulling power, whatever seems pretty irrelevant to the typical cruising boat. Range under power is a lot more important to me.
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Old 07-12-2015, 20:21   #5
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Re: Tug of War - Electric vs Diesel

> Assuming this was done legitimately

BIG assumption!

First thing I noticed was that before they engaged the engines, the electric boat was moving forward and the diesel boat was going backwards.

Then I looked in slomo at the prop wakes from where they started motoring ar the 15 second point to 17 seconds. There is no sign of any prop wash coming from the back of the diesel boat - just a bit coming straight out to the side. Something is very wrong there.
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Old 07-12-2015, 20:26   #6
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Re: Tug of War - Electric vs Diesel

Regarding relevancy, and assuming all other factors such as prop selection etc are balanced out, which boat would push against waves, high winds & currents more efficiently?
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Old 07-12-2015, 20:32   #7
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Re: Tug of War - Electric vs Diesel

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> Assuming this was done legitimately

BIG assumption!

First thing I noticed was that before they engaged the engines, the electric boat was moving forward and the diesel boat was going backwards.

Then I looked in slomo at the prop wakes from where they started motoring ar the 15 second point to 17 seconds. There is no sign of any prop wash coming from the back of the diesel boat - just a bit coming straight out to the side. Something is very wrong there.
I wondered about that too, StuM.

It's not exactly a controlled scientific test, but from what I hear it's not a con job either.

The question in my mind is if the diesel boat is at full revs but being dragged backwards, would the prop wash extend past the hull ends? I'm not sure one way or the other.
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Old 07-12-2015, 20:45   #8
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Re: Tug of War - Electric vs Diesel

This whole scenario doesn't make sense to me. After all, isn't 10kw the same as 13 1/2 HP?

Are they really suggesting that two 14hp engines can out do two 28hp engines?
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Old 07-12-2015, 20:54   #9
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Re: Tug of War - Electric vs Diesel

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This whole scenario doesn't make sense to me. After all, isn't 10kw the same as 13 1/2 HP?

Are they really suggesting that two 14hp engines can out do two 28hp engines?
Yes.
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Old 07-12-2015, 21:00   #10
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Re: Tug of War - Electric vs Diesel

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Originally Posted by BigBeakie View Post
Regarding relevancy, and assuming all other factors such as prop selection etc are balanced out, which boat would push against waves, high winds & currents more efficiently?
Quite!

It's about the same as comparing a steam engine and an agricultural tractor by doing a "tractor pull". The steam engine also has max torque at 0 RPM and should "win" every time. That doesn't necessarily make it the best vehicle for around the farm.
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Old 07-12-2015, 21:06   #11
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Re: Tug of War - Electric vs Diesel

Quote:
Originally Posted by Rustic Charm View Post
This whole scenario doesn't make sense to me. After all, isn't 10kw the same as 13 1/2 HP?

Are they really suggesting that two 14hp engines can out do two 28hp engines?
They are suggesting that two 14HP engines of a type with a particular torque curve can out do two 28HP engines with a totally different torque curve if they are tested in very limited conditions which heavily favour the first type.
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Old 07-12-2015, 21:08   #12
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Re: Tug of War - Electric vs Diesel

There are so many ways that this sort of comparison can be skewed, either deliberately or through ignorance or chance, that it is meaningless. And as others have already said, even if totally correct, the static bollard pull is not relevant to our sailing/motoring practices.

Waste of bandwidth!

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Old 07-12-2015, 21:22   #13
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Re: Tug of War - Electric vs Diesel

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Originally Posted by StuM View Post
They are suggesting that two 14HP engines of a type with a particular torque curve can out do two 28HP engines with a totally different torque curve if they are tested in very limited conditions which heavily favour the first type.
Well StuM, if both propulsion systems were being operated at full throttle ( lets assume that), then how is the diesel at a fundamental disadvantage?

The diesels are developing their full torque (at max revs) while, as another poster pointed out, the electric max torque is at a lower band of the rev range.

Hmmm?
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Old 07-12-2015, 21:29   #14
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Re: Tug of War - Electric vs Diesel

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Originally Posted by Jim Cate View Post
There are so many ways that this sort of comparison can be skewed, either deliberately or through ignorance or chance, that it is meaningless. And as others have already said, even if totally correct, the static bollard pull is not relevant to our sailing/motoring practices.

Waste of bandwidth!

Jim
Yes, yes, there is prop slip factors (although the boats were moving, it wasn't 100% static bollard pull where cavitation factors dominate) and lots of other physics I'm sure someone will refer to pretty soon, but it's just a bit of fun

Chill

Like the truck tug of wars between Ford F350 vs Dodge RAM, it is pretty meaningless unless you are pulling tree stumps or something.
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Old 07-12-2015, 21:33   #15
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Re: Tug of War - Electric vs Diesel

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Originally Posted by BigBeakie View Post
Well StuM, if both propulsion systems were being operated at full throttle ( lets assume that), then how is the diesel at a fundamental disadvantage?

The diesels are developing their full torque (at max revs) while, as another poster pointed out, the electric max torque is at a lower band of the rev range.

Hmmm?
Full throttle does not necessarily equal max revs. It depends on the respective gearing and prop designs (Try putting your foot hard down while driving a manual car up a hill)
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