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Old 01-10-2017, 03:36 PM   #21
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You could go AC, but would either need a controller or it would have massive start amps. DC motor I think is what would be easiest.

I think motor tech now favors AC using a controller to shape waveform, but at 10hp that is a pretty expensive. DC might be easier.

Regarding the volts, most motors are presently lower volts as they are designed to run on batt banks. To run directly off the gen output it probably would be easier to set up motor for higher volts. Thinking less processing would be needed.

Not sure what would be best. That's for motor engineers to figure out.

I think I've seen AC thrusters refed in some on-line reading? Said to be a good thing?

Our 8 kW genset can run two chargers (40A and 70A) plus two 1600 BTU ACs, water heater, plus cooktop, microwave, etc. -- start-up loads semi-simultaneously, as far as I know -- all at once. Boatload of amps; maybe if all (or most of) that current was channeled into a pod drive instead, it'd be more better (the scientific term, I bet) than a 48V DC pod drive? At least for get-home or emergency steerageway?

Just speculating, without many actual factoids on hand...

-Chris
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Old 01-10-2017, 05:59 PM   #22
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I'm far from an expert, but my understanding is that most large variable speed electric motors are AC, controlled by variable frequency drives. They are essentially inverters where you can control the frequency and voltage to control the speed of an AC motor. Large thrusters, propulsion motors, trains, and electric cars all work this way, as I understand.
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Old 01-20-2017, 10:01 PM   #23
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Electric seems right?

Hello everyone, first post. I have looked at a few options for a get-home system with limited space. So far, an electric (48/72 VDC) driven saildrive seems the best option (but lots of research to do yet). The Oceanvolt unit seems the best do far - simple and enough to push me along at a knot or two. It is not really designed as a get-home, more as power for a sail boat (large battery bank, etc.) What I need is a drive system that will operate off the genset and provide limited forward progress. If anyone has ever installed an Oceanvolt system (or other) in a displacement boat as an aux drive I would really like to hear about it.
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Old 01-21-2017, 02:04 AM   #24
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Hello everyone, first post. I have looked at a few options for a get-home system with limited space. So far, an electric (48/72 VDC) driven saildrive seems the best option (but lots of research to do yet). The Oceanvolt unit seems the best do far - simple and enough to push me along at a knot or two. It is not really designed as a get-home, more as power for a sail boat (large battery bank, etc.) What I need is a drive system that will operate off the genset and provide limited forward progress. If anyone has ever installed an Oceanvolt system (or other) in a displacement boat as an aux drive I would really like to hear about it.
would certainly be a coincidence that here in the TF would be someone with first-hand experience oceanvolt. You can look at their references 14 pages of their web link below. I believe that you can ask the user experience them. there are charter companies and yksityisijä cause the users to be found in the website, FB, twiter, etc. I think you'll want to be contacted by e-mail oceanvolt and chat about your case, you can also ask for references from whom to ask

Oceanvolt blog - Customer stories & events
top right of the page catecories red text you will find installed on your system
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Old 01-21-2017, 07:07 AM   #25
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The electronic alternative to emergency Engine

North Baltic, Our boat is one of the afore mentioned twin engined 55's. A sister ship to Peter's with about 6 fewer feet of waterline and 10 less tons of displacement.

I feel the current problem and why an electric drive for our boat's makes no sense is because diesel fuel and even gasoline for that matter are an order of magnitude higher in energy density than the current state of the art lithium battery systems. A single gallon of diesel weighs only 7 pounds but contains over 40kw of energy. Fully fueled, our boat's carry megawatts of energy onboard ready to use. Even considering the efficiency losses in diesel propulsion and adding the efficiency gains from D.C. motors in electric propulsion, we still need more kw of electricity than battery banks can carry. Any efficiency gained via the D.C. motor slowly disappears once you start replenishing it with a diesel generator/shore power.

It's all in the numbers.

1hp is still about 750 watts and yes that means your wife's hair dryer is 2 hp.

Hydraulics, 1 GPM at 1500 psi also equals 1 hp.

1gal of diesel contains about 40,400 watts of energy.

Current state of the art electric propulsion motors might be 3 times more efficient per kw than diesel, but those kw also come out of a battery bank faster than sun wind or even diesel generators can replace them.

For some boat's and owners like Donald Street and Iolaire it might work. Note, Street did take the engine out and sailed her over 200,000 before going back to a diesel electric auxiliary in 2007.

The Russians use nukes and steam turbines powering dynamos outputting 10,000 VDC. to turn the props on their arktika class ice breakers. .2kg of uranium per day when breaking 3 meters of ice gives them 13 years of stored energy to use during their voyages. A kilowatt is still a kilowatt, no matter the source.

Selene48 welcome to the forum, you might try a google search for iolaire or Donald Street for some info. He has had a love hate relationship with auxiliary power his whole life.
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Old 01-21-2017, 09:21 PM   #26
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I'm far from an expert, but my understanding is that most large variable speed electric motors are AC, controlled by variable frequency drives. They are essentially inverters where you can control the frequency and voltage to control the speed of an AC motor. Large thrusters, propulsion motors, trains, and electric cars all work this way, as I understand.
I think you are right, but in all my searching I have not been able to find a variable speed/frequency AC motor in the size I need (say 10 to 15 kW). The only motors I have found are DC driven indirectly by a genset via a battery bank/controller. Some have been adapted to saildrives (Elco) and some are complete units (Oceanvolt). There may be an obvious reason a variable speed drive cannot be connected to the genset (via a controller) but I have not been able to find anyone that can tell me why this wont work. I have also not been able to find anyone that can tell me why a DC saildrive unit could not (or should not) be used as an after-market aux drive system. Guess I'm hoping someone on the forum has already worked through this.
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Old 01-22-2017, 09:09 AM   #27
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North Baltic, Our boat is one of the afore mentioned twin engined 55's. A sister ship to Peter's with about 6 fewer feet of waterline and 10 less tons of displacement.

I feel the current problem and why an electric drive for our boat's makes no sense is because diesel fuel and even gasoline for that matter are an order of magnitude higher in energy density than the current state of the art lithium battery systems. A single gallon of diesel weighs only 7 pounds but contains over 40kw of energy. Fully fueled, our boat's carry megawatts of energy onboard ready to use. Even considering the efficiency losses in diesel propulsion and adding the efficiency gains from D.C. motors in electric propulsion, we still need more kw of electricity than battery banks can carry. Any efficiency gained via the D.C. motor slowly disappears once you start replenishing it with a diesel generator/shore power.

It's all in the numbers.

1hp is still about 750 watts and yes that means your wife's hair dryer is 2 hp.

Hydraulics, 1 GPM at 1500 psi also equals 1 hp.

1gal of diesel contains about 40,400 watts of energy.

Current state of the art electric propulsion motors might be 3 times more efficient per kw than diesel, but those kw also come out of a battery bank faster than sun wind or even diesel generators can replace them.

For some boat's and owners like Donald Street and Iolaire it might work. Note, Street did take the engine out and sailed her over 200,000 before going back to a diesel electric auxiliary in 2007.

The Russians use nukes and steam turbines powering dynamos outputting 10,000 VDC. to turn the props on their arktika class ice breakers. .2kg of uranium per day when breaking 3 meters of ice gives them 13 years of stored energy to use during their voyages. A kilowatt is still a kilowatt, no matter the source.

Selene48 welcome to the forum, you might try a google search for iolaire or Donald Street for some info. He has had a love hate relationship with auxiliary power his whole life.

hey, I do not know the issue in depth, and is not intended to Ridella matter that I do not feel better.

I know that the big cruise ships such as the allure of the Seas and Oasis of the Seas, the world's bigest cruisers moving electric motors. 4 big ship Wärtsilä diesel generators rotate only generators. The ship moves three AAB Azipod 20mW electric motor with propellers. fuel savings of 10-15% in a traditional shaft propulsion. If the ships are OK to make electricity from a diesel generator and electric motor to drive, so you would think this concludes the financial smaller scale?

I know these ships quite well because I have been provided by a large Turn Key project for these ships.

http://www.abb.fi/cawp/seitp202/33b3...10035b74f.aspx



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Old 01-22-2017, 09:30 AM   #28
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No doubt that the fundamental engineering for an electric get-home system is well established.

Two issues exist, sort of related: First is whether anything already out there on the market can be readily adapted. Looks like the sailboat pods would be ready to bolt on. It would not be practical to design something from scratch considering the cost of such and the small market.

Second is power. For this to work, batteries will not store enough power without being a huge and expensive bank. It will need to be diesel powered in order get the capability to run days on end. Some batteries may be needed for power conditioning for machine startup, etc, but that can be a small bank.

To size a generator large enough to support the get-home, it may be too large to efficiently power normal ship's load.

If you size the generator for the ship's load, it may only be able to power something like a 5hp thruster. That will certainly move a boat in good conditions, but will not be enough to move it against any decent sea or wind. Is that "good enough"? You might be able to choose a downwind course. Maybe.
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Old 01-22-2017, 12:01 PM   #29
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To size a generator large enough to support the get-home, it may be too large to efficiently power normal ship's load.

Another pointer to considering multiple generators, maybe? Each sized for normal ship's load, normally alternate days on each, bring all on line for emergency get-home? Or at least steerage-way?

Would need a boat large enough to accommodate...

Maybe feathering props on the sailboat pod?

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Old 01-24-2017, 11:27 AM   #30
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Just received a set of photos of a Torquedo electric drive installed in a 52'trawler - in the lazarette. Looks like a nice/simple way to add an aux drive. Very few details yet - but will post when I get them. And if I could just figure out how to paste one of the pictures I would.....
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Old 01-24-2017, 11:52 AM   #31
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risk management

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I'm far from an expert, but my understanding is that most large variable speed electric motors are AC, controlled by variable frequency drives. They are essentially inverters where you can control the frequency and voltage to control the speed of an AC motor. Large thrusters, propulsion motors, trains, and electric cars all work this way, as I understand.
The installed base of railed traction motors are primarily DC. Series wound DC motors, not requiring electronics for control. More modern implementations (hi-speed rail, etc) are AC motors driven by IGBT semiconductors; ie, variable frequency drives. AC motors enjoy brushless, no commutators, lower MOTOR maintenance. At the risk of lower control reliability.

I'm a newcomer to this thread; but it would seem reasonable to someone in the know to list the primary faults one is trying to mitigate with this emergency get-home system.

A list like this:

1) out of fuel
2) prop/shaft fouled
3) loss of controls
4) fused semiconductors in the prime mover due to lightning
5) loss of lube oil in the prime mover
6) shaft breakage
7) contaminated fuel
8) grounding damage
9) transmission clutch damage/slipping


If done in a top to bottom order of likelihood, I do believe this would help on choosing a get-home solution.

I'm been aboard some very large vessels, operating with risky cargo, far from port, with just one prime mover and no secondary. It comes down to acceptable reliability. Two engines, a generator can and do die simultaneously with one lightning hit. A single steam engine won't.
Maybe this is generally an unsolvable equation for a sub 100' boat, not sure.
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