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07-12-2015, 18:59
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#1
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Registered User
Join Date: Jan 2014
Location: Coffs Harbour, NSW
Boat: FreeFlow 50 cat
Posts: 1,336
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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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07-12-2015, 19:40
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#2
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Registered User
Join Date: Mar 2009
Location: Southern Chesapeake Bay
Boat: Norseman 430, Jabberwock
Posts: 1,405
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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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07-12-2015, 19:51
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#3
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Registered User
Join Date: Feb 2013
Location: WY / Currently in Hayes VA on the Chesapeake
Boat: Ocean Alexander, Ocean 44
Posts: 1,149
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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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07-12-2015, 20:13
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#4
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Senior Cruiser
Join Date: Oct 2007
Location: 29° 49.16’ N 82° 25.82’ W
Boat: Pearson 422
Posts: 16,306
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by ggray
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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Exactly. Torque, pulling power, whatever seems pretty irrelevant to the typical cruising boat. Range under power is a lot more important to me.
__________________
The water is always bluer on the other side of the ocean.
Sometimes it's necessary to state the obvious for the benefit of the oblivious.
Rust is the poor man's Loctite.
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07-12-2015, 20:21
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#5
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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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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07-12-2015, 20:26
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#6
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Registered User
Join Date: Jan 2014
Location: Coffs Harbour, NSW
Boat: FreeFlow 50 cat
Posts: 1,336
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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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07-12-2015, 20:32
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#7
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Registered User
Join Date: Jan 2014
Location: Coffs Harbour, NSW
Boat: FreeFlow 50 cat
Posts: 1,336
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by StuM
> 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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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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07-12-2015, 20:45
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#8
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Registered User
Join Date: Jun 2011
Location: Tasmania, Australia
Boat: Bieroc 36 foot Ketch
Posts: 4,952
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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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07-12-2015, 20:54
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#9
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Registered User
Join Date: Jan 2014
Location: Coffs Harbour, NSW
Boat: FreeFlow 50 cat
Posts: 1,336
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by Rustic Charm
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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Yes.
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07-12-2015, 21:00
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#10
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by BigBeakie
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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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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07-12-2015, 21:06
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#11
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by Rustic Charm
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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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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07-12-2015, 21:08
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#12
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,134
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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!
Jim
__________________
Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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07-12-2015, 21:22
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#13
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Registered User
Join Date: Jan 2014
Location: Coffs Harbour, NSW
Boat: FreeFlow 50 cat
Posts: 1,336
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by StuM
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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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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07-12-2015, 21:29
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#14
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Registered User
Join Date: Jan 2014
Location: Coffs Harbour, NSW
Boat: FreeFlow 50 cat
Posts: 1,336
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by Jim Cate
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
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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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07-12-2015, 21:33
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#15
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Senior Cruiser
Join Date: Nov 2013
Location: Port Moresby,Papua New Guinea
Boat: FP Belize Maestro 43 and OPBs
Posts: 12,888
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Re: Tug of War - Electric vs Diesel
Quote:
Originally Posted by BigBeakie
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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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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