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Old 17-07-2014, 10:47   #376
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Re: Electric Propulsion on Catamarans

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Originally Posted by BigBeakie View Post
In all the scenarios, the period of motoring is short term, so easily handled by battery .
Typically you can motor quite a while given range/speed tradeoff. In my older electric drive system (inefficient but free brushed motors from 1995) a few times I motored for 20 miles at 2 knots draining my flooded lead acid batteries by half.
Quote:
When the genset is required is when you need to motor for many hours such as when becalmed.
I have been becalmed for days at a time, but there was plenty of sun.
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Originally Posted by valhalla360 View Post
That was in refernce to a pure solar/electric model (ie: no genset) and without making other extreme compromises, I think it's pretty realistic.
It is unrealistic. Going without wind or sun for days at a time is incredibly unlikely. In fact on wind alone, you can normally assume you won't be becalmed for long periods with proper planning.
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If you want typical cruise speeds under power you need typical HP. There is no magic to electric motors that allows a 1hp electric to produce the forward thrust of a 50hp diesel. Assuming the exisiting direct drive diesel is appropriately sized for the boat, cruise speed should have the motor running very efficently.
The "magic" is in the reduced frictional losses (no belts alternators etc) and also by using a very large propeller spinning slowly. Typical direct drive systems convert less than 5% of the energy in the fuel into forward thrust. We can convert upwards of 70% of of the battery energy into forward thrust. Ships, and submarines already use large propellers for efficiency reasons.

This applies to any type of drive system. There is a reason my sculling oar is 2/3 the length of the boat, moves at 20 rpm, and pushes the boat 1.5 knots using 1/8th of a horsepower.

The problem is, many people are stuck in the past when they didn't care about efficiency because fuel costs were incredibly low. Because of this, the convenience of a small propeller and not needing the level of gear reductions was selected and widely adopted.

It is no longer a good design choice for cost or efficiency, but the same is true of cars on roads when we could be using cars hanging from steel cables with grass growing where pavement now exists.
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Old 17-07-2014, 12:53   #377
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Re: Electric Propulsion on Catamarans

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Originally Posted by boat_alexandra View Post
Typically you can motor quite a while given range/speed tradeoff. In my older electric drive system (inefficient but free brushed motors from 1995) a few times I motored for 20 miles at 2 knots draining my flooded lead acid batteries by half.

I have been becalmed for days at a time, but there was plenty of sun.
But the sun won't provide cruise speed.

Quote:
Originally Posted by boat_alexandra View Post
It is unrealistic. Going without wind or sun for days at a time is incredibly unlikely. In fact on wind alone, you can normally assume you won't be becalmed for long periods with proper planning.
You are capable of planning the weather? Where do you place the order?

As I stated, there are schedules to keep, however bad they conflict with weather and cruising, it does happen.


Quote:
Originally Posted by boat_alexandra View Post
The "magic" is in the reduced frictional losses (no belts alternators etc) and also by using a very large propeller spinning slowly. Typical direct drive systems convert less than 5% of the energy in the fuel into forward thrust. We can convert upwards of 70% of of the battery energy into forward thrust.
Now, tell the 'real' efficiency when charging the battery using diesel. That's what cruisers are interested in.


Quote:
Originally Posted by boat_alexandra View Post
Ships, and submarines already use large propellers for efficiency reasons.

This applies to any type of drive system. There is a reason my sculling oar is 2/3 the length of the boat, moves at 20 rpm, and pushes the boat 1.5 knots using 1/8th of a horsepower.

The problem is, many people are stuck in the past when they didn't care about efficiency because fuel costs were incredibly low. Because of this, the convenience of a small propeller and not needing the level of gear reductions was selected and widely adopted.

It is no longer a good design choice for cost or efficiency, but the same is true of cars on roads when we could be using cars hanging from steel cables with grass growing where pavement now exists.
And Betamax was better than VHS.....
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Old 17-07-2014, 12:58   #378
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Re: Electric Propulsion on Catamarans

Compare Diesel vs Gasoline Side-by-Side

Check out the turbo diesel vs gasoline..

In my view, one can take a prius drivetrain and put it in each hull of cat,
and now you have two generators, two engine driven props, and two electric driven props. The electric motors outlast the gasoline engines by far,
a recent one for sale had 300,000 miles and finally the engine was going bad.

These cars can be bought for under $10,000 each, that is $20,000 for two.

Parts and service can't get any easier when over a million have been put in service on the road.
I'd be glad to setup anyone's cat with this setup, $50,000 should be no problem, would love to drop all my other projects and get to this one.
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Old 17-07-2014, 13:16   #379
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Re: Electric Propulsion on Catamarans

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But the sun won't provide cruise speed.
1 knot less than hull speed is possible.
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You are capable of planning the weather? Where do you place the order?
I wrote the climatology plugin for opencpn. You can download it here: http://opencpn.org/ocpn/downloadplugins
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Originally Posted by nimblemotors View Post
oline..

In my view, one can take a prius drivetrain and put it in each hull of cat,
and now you have two generators, two engine driven props, and two electric driven props. The electric motors outlast the gasoline engines by far,
a recent one for sale had 300,000 miles and finally the engine was going bad.
I think potentially a good option for someone
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Old 17-07-2014, 14:09   #380
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Re: Electric Propulsion on Catamarans

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Originally Posted by boat_alexandra View Post
It is unrealistic. Going without wind or sun for days at a time is incredibly unlikely. In fact on wind alone, you can normally assume you won't be becalmed for long periods with proper planning.


The "magic" is in the reduced frictional losses (no belts alternators etc) and also by using a very large propeller spinning slowly. Typical direct drive systems convert less than 5% of the energy in the fuel into forward thrust. We can convert upwards of 70% of of the battery energy into forward thrust. Ships, and submarines already use large propellers for efficiency reasons.

This applies to any type of drive system. There is a reason my sculling oar is 2/3 the length of the boat, moves at 20 rpm, and pushes the boat 1.5 knots using 1/8th of a horsepower.

The problem is, many people are stuck in the past when they didn't care about efficiency because fuel costs were incredibly low. Because of this, the convenience of a small propeller and not needing the level of gear reductions was selected and widely adopted.

It is no longer a good design choice for cost or efficiency, but the same is true of cars on roads when we could be using cars hanging from steel cables with grass growing where pavement now exists.
You glossed over a key point. I was talking about typical cruisers of which the vast majority are coastal and the vast majority aren't going to turn a 40 mile run into a 3 days of contious travel just to claim they didn't crank up the diesel.

You are talking about a very specific subset of cruisers who simply don't care when they get there. Thats fine but setting the bar based on this niche won't result in mainstream commercial applications.

Your 5% statement is misleading at best. Those batteries that get 70% efficency hold a tiny fraction of the power of a single gallon of diesel. Then you overlook the costs associated with generating the power. Even with solar, there is the cost of producing the panels which drastically reduces your 70% number. More importantly, there isn't enough room to put on enough solar to maintain solar for any reasonable time period.

Reality is we were talking about available power. Someone a while back was claiming a 10hp electic motor was equivilent to a 30hp diesel and that is patently false. I believe the claim was you could pump more electricity thru the motor to put out more HP. Well you can monkey with the diesel and increase the turbo to have it put out more HP also. No manufacturer is going to rate the motor at 10hp if you can really get 30hp out of it (look at generator ratings which are always rated based on peak output)

The big prop (or sculling oar) isn't why you need very little power to go 1.5kts. You need very little power to go 1.5kts because it takes very little power (electic or diesel) to go 1.5kts. If you put the 30hp diesel in gear at idle, it's putting out no where close to 30hp. Since no one travels long distances at 1.5kts, it's not really relevant but it shows the problem with a solar/electric system, to work it requires compromises that the vast majority of cruisers won't make when they are already drastically more efficent than anyone else.
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Old 17-07-2014, 15:26   #381
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Re: Electric Propulsion on Catamarans

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Originally Posted by BigBeakie View Post
343

Mate, you are all over the shop. In your post #326 you said there were 5 failures , then in your post #343 you said there were 7 replacements, now you are back to 5 failures.

Claude at Torqeedo has records of all of this, on paper in black & white. But regardless of the exact number of failures vs replacements, what you are asking us to believe is that 1 customer has the statistically improbable event that 3, 5 or 7 (whatever) Cruise 4 are faulty in a row. Nothing to do with what the owner is doing, of course. Of course not

So by that reasoning, there should lots of Torqeedo users with units failing all over the place. Right? Because obviously the quality control and/or the design of Torqeedo's must be awful, right? Why would Brian be singled out to get so many faulty units, time after time, unless everybody else was having the same experience? Right?

I put it to you, that is not the case. If you have any meaningful evidence to the contrary, lets hear it.

But really, I would be genuinely interested to learn that all the users I checked that are happy with their one time Torqeedo purchase ( no replacements ever) are among those rare Torqeedo customers who have NOT had a problem. Who woulda figured that could happen?
Obviously your powers of comprehension are lacking. Or you argue with other people without even reading their posts. Or you can't count.

Try this: 2 e-pod failures + 5 Torqeedo failures. 2+5.

Hint: it comes to 7.

Why would they fail on that particular boat? Pretty simple - it was very probably the first and at the time only instance where they had been used on a big cruising boat, operating at near full power for long periods in salt water.

Anyway, forget about School's Out. Never happened right? I made it all up. Bryan probably just got rid of them, and went to the expense and hassle of slipping his boat and retrofitting an outboard motor, because he didn't like the colour.

Buy them.

Those Deep Blues look awesome! 40 hp, enough batteries to motor maybe 100 miles, and only 800 lbs! And at only $36500 (US) (plus installation) an absolute STEAL.

Go for it! Please, buy them.
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Old 17-07-2014, 15:34   #382
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Re: Electric Propulsion on Catamarans

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Originally Posted by boat_alexandra View Post
1 knot less than hull speed is possible.
On my boat, I figure that takes ~26hp. How many watts from solar panels would that be?

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Originally Posted by boat_alexandra View Post
I wrote the climatology plugin for opencpn. You can download it here: PlugIns | Official OpenCPN Homepage
You missed my point....unless you can use your plugin to order the kind of weather you want. To a cruiser, weather planning equates to staying put until the weather is conducive to a "nice" passage. With diesel, I have the option of going when the weather is conducive to a "lesser than nice" passage.

So, I'm back to the question you seem to be side-stepping. What is the comparison of efficiency between direct diesel drive vs. diesel generated electric drive?

Then the follow-on questions....

Cost
Simplicity
Reliability
Longevity of the system
Redundancy
Availability of parts
Availability of technical expertise
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Old 17-07-2014, 16:42   #383
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Re: Electric Propulsion on Catamarans

This thread drifts all over the place because at any given time people are talking about different subjects viz a viz

(a) Solar powered boats - these exist and if the boat is light enough and the solar large enough can be made to work, but is not practical for normal cruising

(b) Those that want to put electric motors on with standard equipment as exists today

(c) Those that think electric motors will be viable in boats in the future e.g. the two prius motors example

There is no doubt in my mind that when one looks at the calculations an electric motor system that is fully integrated is more efficient than diesels. The prius motors are a good example. We are only lacking about $100 mill of R&D to design a specially created marine system. With respect to nimble he aint going any where near a boat I own.

So in ten years I have no doubt the majority of new boats will be electric, but now we are talking about using standard parts to form a system, and I see too many problems with this approach. It is not only "schools out" that had a problem. The original Corsair 50's were equipped with electric motors and had to be changed out. Various production suppliers have tried and failed.

This will not work until someone designs a system with a fully integrated approach.
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Old 17-07-2014, 17:43   #384
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Re: Electric Propulsion on Catamarans

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1 knot less than hull speed is possible.

)
Agreed.

I don't have to guess. Even with my heavy 13 ton boat and a somewhat inefficient hull design (semi-displacement ) We are talking a 1972 41 foot Chris-craft Commander, one of the heaver fiberglass boats ever built, I can cruise at 4 knots on a sunny day with my 3kw array with no draw on the battery bank. But even with no sun my range with my 48kw battery bank would be around 100 miles at the before noted 4 knots.

I still have room to improve my numbers. But given that my boat is kind of a worst case as far as boats to convert, almost anyone else should get much better numbers. The Cats we are talking about could have 5kw or even 6kw solar arrays. I would expect there solar cruise speed to be 5-6 knots.
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Old 17-07-2014, 17:55   #385
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Re: Electric Propulsion on Catamarans

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Can you show me where I have said anything you claim I've said?
That diesels are more reliable than industrial electric motors.

"No boat owner should rely on electric drive with current technology, as there are times you need your engines when things go bad out there. "
I guess someone else posted the above message using your account? Or you might want to see a doctor about being tested for dementia, because the post is not far enough back that you should have already forgotten it.
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Old 17-07-2014, 17:55   #386
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Re: Electric Propulsion on Catamarans

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Originally Posted by valhalla360 View Post
Reality is we were talking about available power. Someone a while back was claiming a 10hp electic motor was equivilent to a 30hp diesel and that is patently false. I believe the claim was you could pump more electricity thru the motor to put out more HP. Well you can monkey with the diesel and increase the turbo to have it put out more HP also. No manufacturer is going to rate the motor at 10hp if you can really get 30hp out of it (look at generator ratings which are always rated based on peak output)
No one has claimed a 10HP electric motor is equivalent to a 30HP diesel motor. Quite the opposite in fact. In my experience this sort of misunderstanding crops up a lot in these discussions.

Electric motors are typically rated at continuous power. Diesel engines are typically rated at peak power.

If your boat needs 10HP to move at cruise speed in normal conditions, then a 30HP peak rated diesel or a 10HP continuous rated electric motor will do the same job (leaving aside efficiency differences for now). What people forget is that the 30HP diesel won't be producing 30HP at cruise speed - only 10HP. There is no mystery, or free power - it's basic maths.

Electric motor have a peak power rating too (whether it is given or not), but it's not a continuous rating. Many can exceed the continuous rating for a certain period of time but the peak power rating is time constrained, usually from overheating. A diesel engine can output peak power for a lot longer than an electric motor. If you need 30HP continuous, then you need an electric motor rated at 30HP continuous. A 10HP electric motor will not replace a 30HP diesel engine that is actually producing 30HP.

Electric motor manufactures generally give continuous rating on the motors because they are mostly used in applications where only the continuous operation is needed. For some applications, peak power (and how long it can deliver it) is important to know and will be given.


There is no magic, or false claims or free power involved. It is basic maths and understanding the difference of how power is rated depending on use.
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Old 17-07-2014, 19:38   #387
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Re: Electric Propulsion on Catamarans

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There is no doubt in my mind that when one looks at the calculations an electric motor system that is fully integrated is more efficient than diesels. The prius motors are a good example. We are only lacking about $100 mill of R&D to design a specially created marine system.
There are a few factors that I think are often overlooked that make hybrid electric cars and hybrid electric boats a very different proposition.

Cars spend a large portion of their use accelerating, cruising for a short while then braking. Each time they brake, energy is lost as heat. A hybrid system can instead capture some of that braking energy and store it for the next acceleration. By re-using some of the energy, less fuel needs to be burnt, offering significant efficiency improvements.

On a boat under power, typically you cruise at a constant speed and no regenerative braking style system is possible. This means boats can't really take advantage of one of the major efficiency improvements that cars can.


Hybrid systems have other advantages too - such as being able to run the motor at it's most efficient speed, instead of having to vary the speed. In cars, the engine speed varies at a lot, so this makes a decent improvement to efficiency. In a boat, engines will often run for long periods at a specific speed for cruising. If the engine is well matched to the boat, then it can run at it's most efficient speed most of the time anyway.


For boat use electric drive systems can improve efficiency in a number of areas. Electric motors are better suited to spin a large, slow turning propeller without needing a reduction gearbox (or only a very simple one). With the right setup, more of your motor power can be turned into thrust.

The problem is that even with an efficient generator, you get losses through the system which work to cancel our the efficiency gains. Once you start factoring in charging and discharging batteries, the efficiency is further lowered. New technologies are reducing these losses along the way, but a hybrid system does not give the same efficiency improvements in a boat as it does in a car.



I think electric motor use in boats will become increasingly common for the other benefits it gives.

Electric motors make for good manoeuvring - they can reverse very easily and give very precisely controllable and instant thrust.

Electric motors are compact, making them easy to install in areas not possible with a ICE engine. They can also be pod installed. With a small footprint it is easy to have more than one for manoeuvring and redundancy.

With a hybrid system, your ICE engines don't need to be mounted near the propellers. One or more generators can be mounted wherever suits best for layout and balance. It is also easy to soundproof them to a high degree or make them easily removable for servicing.

Electric motors can run near silently with no fumes. With a battery storage system you can cruise without needing to use your generators all the time.

With a large solar array plus wind and hydro power generation, you can constantly refill your batteries without needing to fire up the generator. These "Free" top ups greatly increase how far each litre of fuel takes you.

A boat set up for electric motor drive is also well set up for large electric house loads. That might equal more creature comforts or just replacing other fuel sources, such as propane.

While the overall system may be complex, an electric motor itself is simple and has a long life. For total price of mind you could carry a spare easily. With the right system, overall redundancy can be quite good too.

Electric motors combine very well with motor sailing. In light winds a small amount of thrust from the electric motors can boost speeds silently. With the right system you can easily do this from solar power alone.



There are many other advantages too, for both systems. Electric are not without issues though. They are new technology, expensive, can be complex, harder to get repaired or serviced, needs large expanses of solar panels. For fuel savings alone, it would take a long time to pay back the extra cost.

If I was heading off to sail around the world tomorrow, I would not want an electric system. If I was coastal hopping, or cruising around islands etc, then the advantages would be pretty appealing.
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Old 17-07-2014, 20:08   #388
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Re: Electric Propulsion on Catamarans

Thanks handmer for persisting with clearly expressed explanations.

It can be confusing when trying to understand how people get away with smaller electric motors compared to diesel counterparts. Lots of misconceptions crop up.

What I am looking into right now is,

How do you size the prop on an electric motor? How do you actually do it?

The prop companies have the sizing of diesels well understood it seems, because of experience and they know what works. You tell them the type of hull, max displacement, diesel engine HP, gear reduction or rpm of shaft at max engine rpm...and they can tell you the diameter and pitch you will need.
But they will recommend the same prop on an electric motor given the same rpm AT THE PROPSHAFT as the equivalent diesel HP engine. This seems wrong to me. it seems that the prop on the EM should be bigger than the equivalent diesel because the EM can spin a larger prop at lower rpm because of its greater torque capability, and so give more propulsive thrust.

Am I wrong on this? If so, why? And if not, then how do you come up with what size propeller to use?

Sorry for the newbie question, but this one has me head scratching.

The specific example I'm looking at is comparing the prop on the 42HP Yanmar which takes a 17.5 x 11, 3 bladed feathering Autostream prop. The shaft rpm at WOT is 1, 150 rpm.
Comparing to the Torqeedo Deep Blue 40i 40 HP (30kW) shaft drive electric with max shaft rpm at 1,200 rpm. The Torqeedo site lists the propulsive power of that motor at 16.2kW

So use same prop as the Yanmar diesel or a bigger one? If a bigger one, how big and how did you come up with the calculation?

Thanks guys
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Old 17-07-2014, 21:15   #389
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Re: Electric Propulsion on Catamarans

Is there a reason not to use the existing prop from Torqeedo?

I imagine it is not the most efficient design possible, but I also suspect their engineers will have put a fair bit of effort into selecting a good all round prop. If you need to run at speeds outside of what the prop is optimised for, Torqeedo themselves would be my first port of call in asking for recommendations on changing prop. There would be calculations you could do yourself, but I don't know what they are.

I have read about people going for maximum prop efficiency for things like human powered speed records. They seem to go for very long skinny props - much like those used on model aircraft (in some cases actual model aircraft props). The problem with these is stuff getting caught on the props - an all purpose design needs to be able to shed weed etc, not just give the best efficiency.

Some of the more exotic semi surfacing props used on the bigger solar boats are probably a good mix of efficiency and real world usability, but then I would think they are fairly specific to their exact application.


You are correct though in that ideally you need to size your prop for torque at a given RPM, not just RPM. The shape of the prop will vary too, depending on what speed you want (with the resistance of your hull) at what RPM.
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Old 17-07-2014, 21:30   #390
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Re: Electric Propulsion on Catamarans

I do not know if Torqeedo supplies a "one size fits all" prop for the shaft drive. I doubt it because there would be a wide variety of boat parameters to consider such as single hull or multi, DWL displacement etc.

Basically I'm wondering how anyone who has EM's on their cat sized the propeller? I hope there is some rationale to it other than guesswork.
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