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Old 16-07-2014, 22:21   #361
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Re: Electric Propulsion on Catamarans

Torqeedo had nothing bigger back then. And the e-pods were just junk.
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Old 16-07-2014, 22:36   #362
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Re: Electric Propulsion on Catamarans

Could I please clarify. It appears to me the bottom line here is that electric motors are more efficient that diesels, but assuming a reasonable size solar bank on a cruising yacht, a generator is still required, the generator using considerably less fuel than equivalent diesels.

So does this not mean that we go from the backup redundancy of two diesels on a cat to a single point of failure in regards to the generator. Surely, murphy's law will dictate that at the crucial time when power is needed to get out of a sticky situation, will be the time when the generator needed to cut in to replenish battery power and generator failure at that time could be catastrophic.

What am I missing?
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Old 16-07-2014, 22:46   #363
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Re: Electric Propulsion on Catamarans

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No, it was a statement of FACT. There were FIVE failures of the Torqeedos. You seem to have been given the impression there were three.

I have no axe to grind. I've never owned a Torqeedo, and I'm not likely to,
so it's no problem to me.

In fact I'll even encourage you to go ahead with them. Go for it.
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?
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Old 16-07-2014, 23:09   #364
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Re: Electric Propulsion on Catamarans

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Originally Posted by cwjohm View Post
Could I please clarify. It appears to me the bottom line here is that electric motors are more efficient that diesels,
Can be more efficient, and usually are, but there are plenty of ways to make them inefficient.

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but assuming a reasonable size solar bank on a cruising yacht, a generator is still required, the generator using considerably less fuel than equivalent diesels.
Considering the fact that the motors are not required in the first place, no.

As a general calculation, with an efficient drive system (ie: not torqeedo) and enough solar panels to cover the entire deck area, you can achieve 1 knot below hull speed in full sun on typical cruising boat (with clean bottom). It takes substantially less power to go slower, so with a much smaller array, it is possible to continuously move at 2 and 3 knots, and of course, much faster when draining the battery. This performance is convenient for a wide range of situations. Most places you aren't going to be becalmed for long enough to drain the battery, and then you are off again recharging from hydro.
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Old 16-07-2014, 23:11   #365
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Re: Electric Propulsion on Catamarans

cwjohn,

Sort of but not really. How's that for clarity

Getting out of "sticky situations" sort of implies that you need max power. But for how long will you need it? That power will come from the motor batteries if it isn't a long time (several hours) at max power, so no problem as long as batteries are faithfully topped up after they've been used.

What I've been considering that looks good is having a Watt&Sea Hydrogenerator as a reasonable redundancy solution. So if the gennie quits and you've still got wind, you can get 48amps back in the batteries at 9 knots boatspeed.

If the genset quits and you are becalmed, get the fishing rods out and relax for awhile
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Old 16-07-2014, 23:19   #366
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Re: Electric Propulsion on Catamarans

So single diesel engine monohulls are deathtraps?

Quote:
Originally Posted by cwjohm View Post
Could I please clarify. It appears to me the bottom line here is that electric motors are more efficient that diesels, but assuming a reasonable size solar bank on a cruising yacht, a generator is still required, the generator using considerably less fuel than equivalent diesels.

So does this not mean that we go from the backup redundancy of two diesels on a cat to a single point of failure in regards to the generator. Surely, murphy's law will dictate that at the crucial time when power is needed to get out of a sticky situation, will be the time when the generator needed to cut in to replenish battery power and generator failure at that time could be catastrophic.

What am I missing?
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Old 17-07-2014, 00:24   #367
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Re: Electric Propulsion on Catamarans

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If the genset quits and you are becalmed, get the fishing rods out and relax for awhile
And the sun isn't shining, and your batteries are completely drained. That's the idea
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Old 17-07-2014, 03:34   #368
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Re: Electric Propulsion on Catamarans

Alexandra

I accept for a light enough boat and a big enough solar array what you say is correct. This is a far cry from the typical cruising boat.

nimble

I do not know by what sort of contorted logic you would make such a statement so I have no comment. Suffice it to say one of the advantages of catamarans is the redundancy of propulsion. It is reasonable to question whether that advantage disappears with electric motors.

Rob

The problem is in your definition of "faithfully topped up". In the scenario I described the Voltage Sensitive Relay or computer or whatever is just at the point where it is about to energise the generator. If you set this level to an amount which allows for plenty of battery capacity to get you out of difficult situations then that generator is going to energise regularly including the middle of the night. If you set it at a lower setting then you may not have the capacity to get you out of trouble.
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Old 17-07-2014, 07:14   #369
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Re: Electric Propulsion on Catamarans

Hi Chris,

Not really following your train of thought. Are you saying you would want to run the motors off the genset when you really needed max propulsion? If so, why?

I would think you'd want to draw from the battery for full power as long as it was for a period where the battery wouldn't be drained. A previous post I asked for feedback on what scenarios would you want WOT power. In all the scenarios, the period of motoring is short term, so easily handled by battery .

When the genset is required is when you need to motor for many hours such as when becalmed.

Am I mis-understanding you?
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Old 17-07-2014, 07:20   #370
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Re: Electric Propulsion on Catamarans

This is all about Torqueedo. This is what I am currently lusting after: http://www.elcomotoryachts.com/electric-or-hybrid.shtml

I use elco industrial motors as an engineer. They are a good product. This marine thing appears to be something they pioneered decades ago. Today's battery advancements brought it off the back burner.

Sent from my SM-N900V using Cruisers Sailing Forum mobile app
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Old 17-07-2014, 07:56   #371
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Re: Electric Propulsion on Catamarans

OK, only looking at this thread on an adhoc basis....I'm trying to get a feel for any consensus...

Am I to believe it's more efficient (as in fuel economy) to cruise with an electric motor powered by a diesel generator than to propel a boat with a direct diesel drive?

I don't subscribe to the notion that large battery banks and solar panels will be enough for propulsion. Due to schedules, I've motored at 90% hull speed for 60+ hours, hence that is a benchmark my propulsion system must meet. I know how much fuel I would burn with my direct diesel drive, my question is, what would the difference be powering electric motors to do the same?
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Old 17-07-2014, 09:07   #372
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Re: Electric Propulsion on Catamarans

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OK, only looking at this thread on an adhoc basis....I'm trying to get a feel for any consensus...

Am I to believe it's more efficient (as in fuel economy) to cruise with an electric motor powered by a diesel generator than to propel a boat with a direct diesel drive?

I don't subscribe to the notion that large battery banks and solar panels will be enough for propulsion. Due to schedules, I've motored at 90% hull speed for 60+ hours, hence that is a benchmark my propulsion system must meet. I know how much fuel I would burn with my direct diesel drive, my question is, what would the difference be powering electric motors to do the same?
No a diesel driving a generator to produce electricity run an eletcric motor to power the prop is not more efficent for a small pleasure boat drivetrain and it introduces additional complexity, so reliability is likely lower.

Your usage schedule is much closer to the typical cruiser and is likely the reason why solar/battery systems haven't left the experimental (or those who do it on principal) niche.

Solar/Electric can work fine if:
- You just need it to get away from dock/anchorage and back in. Of course, if that's your only use, you aren't cutting your fuel usage by more than a gallon or two per year and you are probably sacraficing resale value as it's a one-off system.
- You don't mind drifting at 1-3kts for hours or days at a time. Keep in mind this forum/thread is probably heavy on these types of cruisers so don't consider it typical.
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Old 17-07-2014, 09:30   #373
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Re: Electric Propulsion on Catamarans

I think your statement that you will drift around for days at 1 to 3 knots is a bit pessimistic. A fixed rpm DC diesel genset is quite efficient in fuel usage for the kW it produces and if you have correctly sized EM and prop efficiency, you can make much better numbers than those.

valhalla, But you won't get 90% of hull speed unless it is a seriously big genset. If that is your performance requirement, I don't think EM is the way to go. I am prepared to be corrected though.
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Old 17-07-2014, 09:46   #374
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Re: Electric Propulsion on Catamarans

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No a diesel driving a generator to produce electricity run an eletcric motor to power the prop is not more efficent for a small pleasure boat drivetrain and it introduces additional complexity, so reliability is likely lower.

Your usage schedule is much closer to the typical cruiser and is likely the reason why solar/battery systems haven't left the experimental (or those who do it on principal) niche.

Solar/Electric can work fine if:
- You just need it to get away from dock/anchorage and back in. Of course, if that's your only use, you aren't cutting your fuel usage by more than a gallon or two per year and you are probably sacraficing resale value as it's a one-off system.
- You don't mind drifting at 1-3kts for hours or days at a time. Keep in mind this forum/thread is probably heavy on these types of cruisers so don't consider it typical.
I obviously have other criteria, but range at reasonable speed shares #1 spot on the list.

Other criteria include:

Cost
Simplicity
Reliability
Longevity of the system
Redundancy
Availability of parts
Availability of technical expertise
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Old 17-07-2014, 09:48   #375
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Re: Electric Propulsion on Catamarans

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I think your statement that you will drift around for days at 1 to 3 knots is a bit pessimistic. A fixed rpm DC diesel genset is quite efficient in fuel usage for the kW it produces and if you have correctly sized EM and prop efficiency, you can make much better numbers than those.

valhalla, But you won't get 90% of hull speed unless it is a seriously big genset. If that is your performance requirement, I don't think EM is the way to go. I am prepared to be corrected though.
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.

Yes, you can run a big genset and power electric motors but that defeats the idea of making an efficent drivetrain. The only advantage I see is you can run A/C, electric stove, electric fridge and just about anything else you can think of while at anchor (assuming you have a big enough fuel tank)

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.
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