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Old 19-02-2015, 17:03   #121
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Re: Using electric motors instead of Diesel on your cat

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Originally Posted by Going Walkabout View Post
CW Thanks. You have settled the argument for me. I'm going to keep with diesel and get the best Solar and battery combination money can buy. I do love my creature comforts.

thanks.
Yep me too

I've been following this thread with interest because I'm going to need to repower my 38 HP. But it seems the reality for those of us who want to be practical and economic, diesel is the way to stick with. by a long long shot.
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Old 22-02-2015, 17:11   #122
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Re: Using electric motors instead of Diesel on your cat

When we think of e power cats, one naturally thinks of the failed Lagoon. However, there is a new example with current technology. I'm curious to see how it proved successful.

Do you know the Gunboat "Moonwave"?

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Old 23-02-2015, 12:57   #123
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Re: Using electric motors instead of Diesel on your cat

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When we think of e power cats, one naturally thinks of the failed Lagoon. However, there is a new example with current technology. I'm curious to see how it proved successful.

Do you know the Gunboat "Moonwave"?

See here Diesel Electric Propulsion post #6, from back in December.

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Old 23-02-2015, 13:39   #124
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Re: Using electric motors instead of Diesel on your cat

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Ok Greg, good idea, let's try a different tack. Let me lay out how this has been put together so we can assess whether it looks like it will do the job, or not. And I am more than happy to hear from those who have a viewpoint based on meaningful analysis ie from direct experience or professional knowledge or real world data. Let's keep the FUD opinions out of this, because it really is not helpful. I am hear to learn, not to be a fanboy of any particular technology. On the other hand, if I am wrong, prove it. Don't expect me to just believe your opinion because you say so. OK?

From hull resistance work and real experience with performance on a sister ship with 39HP Yanmar shaftdrives and Brunton Autoprops, we believe the 30kW electric will produce 6 knots on flat calm with the right size and pitch Kiwiprop for electric using one motor. OK? Lets assume this is true. Kiwiprops feather very nicely, so no more rubbish FUD about dragging around bigger props, OK?

Then we are cruising at 6 knots using 6kW/hour (from a known rpm at a known torque spinning a known propeller spec) which means we can cruise for approx 2 hours until the 13kW Lithium propulsion battery is flat. Yes I know it should not be flattened but kept to 80%DOD.

At that point we start the 6.4kW diesel generator or the 6.5kW petrol Honda (haven't decided which yet) and charge the now depleted battery with 2 (two) 3kW chargers, which should take about 2 hours to rechage. Right? We are now running on the other side motor and battery for the next 2 hours. and so forth, OK?

When the 50 knot wind causes us to drag at anchor we can apply full throttle for about 30 minutes from each motor ( 30kW from 15kW battery), BUT and this is the point I want to make, it will not be necessary to use full throttle because the thrust developed by the high torque electric motor and bigger higher pitched prop will push the boat against the wind without needing to use full throttle.

This seems to be the point that is hard to get across, so let me try an analogy and see if that works.

Let's take 2 extremes. Two boats, one has a 10HP outboard with its normal prop (WOT is say 5,000rpm) and one has a 10HP electric with bigger higher pitched prop (WOT is 2,000 rpm). Stand up to your waist in the water pushing against the bow as the driver puts the outboard in gear and motors against you. Feel the force pushing against you. Get the driver to increase revs slowly until you cannot hold the boat back any longer. Now do same thing with the electric. Take note of the revs of each boat at the point when it would push you over.

What would the result be? I maintain that you would be pushed over by the electric motor at much lower revs than the petrol outboard. I maintain that the outboard will go much faster (planing hull form) at WOT with it's smaller but faster rpm prop than the electric boat at WOT with the bigger, higher pitched, but slower rpm prop.

Furthermore, and this is the main point, I maintain that the electric boat will be able to maintain its lower maximum speed against a bigger force (like the wind) than the outboard, which will slow down more against the wind.

So the point re EP cruising boats is that the electric can be run at lower rpm, and hence less energy drain from battery giving longer run times and range, and still cope with adverse wind and wave conditions.

So it seems to me that with adequate solar, adequate lithium house bank, good generator charging system, reliable EP system from top quality components with built in diagnostics, and a vendor who stands behind the entire system (meaning they fix it no matter what!) regardless of what may develop a fault, it seems to me this has to be taken seriously as a viable cruising EP solution offering many, many advantages.

I am prepared to be convinced otherwise by argument based upon real data or other evidence. If I am right, this is really good news, it seems to me. If I am wrong, then there must be a fault at principle, not execution. Meaning there may be technically inadequate spec somewhere, but that can be modified or fixed. But if the EP system has adequate power motors and sufficient propulsion battery to deal with adverse scenarios, and has reliability & support, then it would seem to be a serious contender.
This is all very well thought through and very interesting, but this bit gives me pause:

"When the 50 knot wind causes us to drag at anchor we can apply full throttle for about 30 minutes from each motor ( 30kW from 15kW battery), BUT and this is the point I want to make, it will not be necessary to use full throttle because the thrust developed by the high torque electric motor and bigger higher pitched prop will push the boat against the wind without needing to use full throttle."

This does not sound right to me -- power -- the ability to do work -- is power. If you need x kW of power, you need x kW of power, not y amount of torque. If it would take 30kW of diesel power to do the job, why should an electric motor be magically able to do it on 15kW? I've heard this before, but it doesn't sound right to me. Work is work, and power is power. Torque is the ability to apply force, but force without more is not work -- these are different things. Electric motors are different from IC -- they have max torque at 0 revs, so they can swing a bigger prop. But 1kW of work done is all the same whether it's produced at 1 rev or 10,000.

Or if I'm wrong -- I'm not engineer -- I would sure be grateful to be enlightened.
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Old 23-02-2015, 15:05   #125
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Re: Using electric motors instead of Diesel on your cat

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Originally Posted by Dockhead View Post
This is all very well thought through and very interesting, but this bit gives me pause:

"When the 50 knot wind causes us to drag at anchor we can apply full throttle for about 30 minutes from each motor ( 30kW from 15kW battery), BUT and this is the point I want to make, it will not be necessary to use full throttle because the thrust developed by the high torque electric motor and bigger higher pitched prop will push the boat against the wind without needing to use full throttle."

This does not sound right to me -- power -- the ability to do work -- is power. If you need x kW of power, you need x kW of power, not y amount of torque. If it would take 30kW of diesel power to do the job, why should an electric motor be magically able to do it on 15kW? I've heard this before, but it doesn't sound right to me. Work is work, and power is power. Torque is the ability to apply force, but force without more is not work -- these are different things. Electric motors are different from IC -- they have max torque at 0 revs, so they can swing a bigger prop. But 1kW of work done is all the same whether it's produced at 1 rev or 10,000.

Or if I'm wrong -- I'm not engineer -- I would sure be grateful to be enlightened.
Dockhead,

You are right. And there is a practical limitation that absent major refit to the boat you just can't add a much larger prop than what diesel boats are already using. Almost every boat is already using a prop at maximum anyway, so the notion of installing a larger prop is just silly.

it might be possible to redesign a keel so the motor is in the bow, and the prop shaft travels thru the keel. Which would allow a larger prop, but absent something like this there just isn't room. or you could use a more substantial down angle, but that would greatly reduce efficiency and increase prop walk so there is a trade off there are well.
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Old 23-02-2015, 15:13   #126
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Re: Using electric motors instead of Diesel on your cat

When we think of e power cats, one naturally thinks of the failed Lagoon. However, there is a new example with current technology. I'm curious to see how it proved successful.

Do you know the Gunboat "Moonwave"?
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Old 23-02-2015, 15:14   #127
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Re: Using electric motors instead of Diesel on your cat

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Originally Posted by Ulstue View Post
When we think of e power cats, one naturally thinks of the failed Lagoon. However, there is a new example with current technology. I'm curious to see how it proved successful.

Do you know the Gunboat "Moonwave"?

Oh, let me run out and buy two of em with my millions.

The future is bright though.
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Old 23-02-2015, 15:33   #128
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Re: Using electric motors instead of Diesel on your cat

When we think of e power cats, one naturally thinks of the failed Lagoon.
Quote:
However, there is a new example with current technology. I'm curious to see how it proved successful.

Do you know the Gunboat "Moonwave"?
Sorry for the hiccup there.

Moonwave is an example of the future. i.e. hybrid technology.

It features 23KW generators on each hull together with electric motors, a 23KWh Li-ion battery bank and a 5KW Li-ion house battery bank. This is all integrated with extensive solar and a control system that allows the drive prop to rotate in order to recharge batteries due to the motion of water, and control the boat.

This has two main benefits from an electrical point of view.

(1) Motor free usage for a certain time (around 2 hours in this case). This will allow the owners to pick up people and motor around for a time sipping champagne without the troublesome issue of noise or fumes.

(2) It ensures that invariably on anchorage there is no need of running a generator as the batteries will have reasonable charge given reasonable use.

The problem is that the system still relies heavily on diesel motors in each hull. The saving in terms of diesel in general cruising will depend on the size of the solar array and the degree to which the reversing props provide charge but compared to the cost the payback will be a hundred years or so.

The fact of the matter is that this rig will cost somewhere between $200K and $300K installed which is of no consequence to a boat worth $3-$4 million maybe saving a couple of thousand in diesel as compared to conventional motors given decent cruising use.

If I was worth $100 million + I would definitely go for a system such as this, remembering that I am paying ridiculous money to get these luxuries and not be deluded into thinking there was some logic behind it.

This is definitely Torqueedo's market for Deep Blue systems as there is plenty of people who have sufficient funds to afford a system like this. It is after all a point of difference and reflects status in a boat.

As to environmental issues the cost to the environment in manufacturing such a beast far outweighs any environmental savings so this argument is again illogical.

The other issue of course is that with all of this weight sailing ability will be compromised. To what degree this happens is unknown but I suspect the owners of Moonwave are not overly concerned. As I understand it this boat spends more time in charter than actually sailed by the owners.

Having said all that this is the way of the future for sure, but the manufacturing costs and technologies related to hybrid motors need to improve significantly, and the energy density of batteries need to increase tenfold for this to be a viable financial proposition for the average cruiser who does not have the available funds to spend on such a proposition.
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Old 24-02-2015, 04:52   #129
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Re: Using electric motors instead of Diesel on your cat

The Gunboat 55 is now standard with electric drives with one DC genorator. The Yanmar Diesels are now a $75,000 option.

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Old 24-02-2015, 06:23   #130
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Re: Using electric motors instead of Diesel on your cat

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This is all very well thought through and very interesting, but this bit gives me pause:

"When the 50 knot wind causes us to drag at anchor we can apply full throttle for about 30 minutes from each motor ( 30kW from 15kW battery), BUT and this is the point I want to make, it will not be necessary to use full throttle because the thrust developed by the high torque electric motor and bigger higher pitched prop will push the boat against the wind without needing to use full throttle."

This does not sound right to me -- power -- the ability to do work -- is power. If you need x kW of power, you need x kW of power, not y amount of torque. If it would take 30kW of diesel power to do the job, why should an electric motor be magically able to do it on 15kW? I've heard this before, but it doesn't sound right to me. Work is work, and power is power. Torque is the ability to apply force, but force without more is not work -- these are different things. Electric motors are different from IC -- they have max torque at 0 revs, so they can swing a bigger prop. But 1kW of work done is all the same whether it's produced at 1 rev or 10,000.

Or if I'm wrong -- I'm not engineer -- I would sure be grateful to be enlightened.
You have it correct. HP is HP. By definition, it doesn't care what the source is.

You might gain a small amount thru efficencies (electric motor may not need a reduction gear because it gets max torque from 0 rpm) but no you aren't going to cut your HP needs in half to achieve the same performance.

As I previously posted, if it was all about turning a bigger prop, they would simply install a reduction gear on the deisel transmission (which they often do) to allow it to turn a bigger more efficent prop. They have already selected a prop of appropriate size to the task.

The example he provided of holding back a large boat is a misunderstanding of mechanical advanage vs HP. If you put a 100hp 4banger in a semi and give it a low enough gear ratio, it will happily pull 80tons up a 8% grade. While it won't be stopped, it will have a drastically lower speed up that grade compared to the standard engine. Holding back a larger prop is effectively the same situation.
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Old 24-02-2015, 06:25   #131
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Re: Using electric motors instead of Diesel on your cat

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The Gunboat 55 is now standard with electric drives with one DC genorator. The Yanmar Diesels are now a $75,000 option.

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I couldn't find anything on the gunboat website about this. Can you provide a link?
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Old 24-02-2015, 23:33   #132
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Re: Using electric motors instead of Diesel on your cat

It's in there current specs and pricing sheet provided by the factory. Not up on site yet. It was a big part of their presentation in Miami. OceanVolt 15kw 48volt motors on saildrives, polar power 20kw 48volt DC diesel gen. 16kw lithium ion phosphate propulsion bank. Top speed 9knts. Weight savings about 2000#s.

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Old 24-02-2015, 23:39   #133
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Re: Using electric motors instead of Diesel on your cat

15 kW = about 20 hp. Can't see that setup being lighter or cheaper than a pair of 30 hp saildrives. Can't really see it being enough for a 55 foot cat' either.


And the genset wouldn't even allow them to both be run flat out.
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Old 24-02-2015, 23:42   #134
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Re: Using electric motors instead of Diesel on your cat

no one said it was cheaper! it the standard now.

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Old 25-02-2015, 00:22   #135
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Re: Using electric motors instead of Diesel on your cat

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no one said it was cheaper! it the standard now.

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If diesels cost $75,000 more doesn't that by definition make the electrics cheaper?

Although I'd like to see how they justify $75k more for a much cheaper setup.
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