Diesel/Electric Propulsion for Sailboats

Discussion in 'Hybrid' started by westsail42, Nov 3, 2005.

  1. SFcruiser
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    SFcruiser Junior Member

    Make sense for daysailers or club racer at local

    Considering the price/performance, it make sense for day-sailers or club racers to installer a small 48V DC motor to get in and out of the harbor when they need to re-power their old diesel engine. They need only four 12V batteries (50 A-hr each; just need it for a while). Batteries can be charged at the dock power - usually its free. For a longer distance trip, just carry a Honda gas generator for safety.

    The overall price is half of a diesel installation and it can be done in an afternoon w/o professional help. It also cut the weight by more than 50%. Guess the competition is a outboard motor setup - its cheaper, light weight but noisy.

    For cruisers, I still don't see a viable solution yet - the overall cost is more than double of a diesel installation. Advantages are not very significant at the current setting (except for big cat).

    From the engineering point of view, the bottleneck of the D/E system efficiency is mainly on the battery technology. All the lead acid batteries, including AGM, are poor on the recharging efficiency. Unless we see the Lithium battery price dropped to a reasonable level (might happen in a couple years due to the development of EV), it is not a good option at this time for cruiser with big demand.

    However, this is not 100% true. There are still cruisers circumnavigating w/o an engine....:p :D

    Cheer!

    SFcruiser
     
  2. SFcruiser
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    SFcruiser Junior Member

    More on efficiency

    Here is more:

    For those cruisers really concern about the fuel consumption to the level of considering D/E system (its possible for a long distance trip and the fuel tank capacity is limited - more important than money saving):

    Option 1: go for the D/E system but consider to install Lithium battery instead. There are package available for the EV. Check: http://www.everspring.net/product-battery.htm. It will be more expensive but its light-weighted and a lot more efficient. You need to change it every 3-4 years no matter your use it or not.

    Option 2: Just put a prop 1-2 inch bigger in diameter and 1-2" larger in pitch. It will move the max output of your diesel to 2000-2500 rpm from 3600 rpm and provide a lot better efficiency at your cruising speed. I bet it can save 30% of the fuel. However, you will lost your engine's max output (you hardly use it but once a while use it in bad situation. You lost that on those P/E system too; for some people, this is more on your skill to avoid troubles instead of an defect). It will create a bigger drag while sailing so you might want to install a one-size bigger 3-blade folding prop (like Max prop). It will cost you $4000-5000 but it is more reliable than those D/E system at this time. Still cheaper!

    SFCruiser
     
  3. FAST FRED
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    FAST FRED Senior Member

    "Option 2: Just put a prop 1-2 inch bigger in diameter and 1-2" larger in pitch. It will move the max output of your diesel to 2000-2500 rpm from 3600 rpm and provide a lot better efficiency at your cruising speed. I bet it can save 30% of the fuel. However, you will lost your engine's max output (you hardly use it but once a while use it in bad situation."

    This is known as a cruising prop and for my bucks is the best way to gain HUGE efficiency on most cruisers.

    Far longer service life , quieter , no wet stacking ,less blowby, less noise and vibration.

    A diesel MUST be loaded to produce good efficiency so pulling back a 100hp unit to 2gph 35 hp does not work as well as reproping to a lower cruise rpm.

    For best results an exhaust gas temp pickup should be installed (about $100 + drilling and tapping) .

    A simple rule of thumb is to operate at full throttle and pull back 10% of the observed RPM.

    Pace a red line at the 10% down rpm and ALWAYS OBSERVE THE LIMIT!!!

    FF
     
  4. thudpucker
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    thudpucker Senior Member

    WOW! I'm impressed with facts. I love to dream and wish, but Facts will bring you back to the four grey walls. You guys are impressive!

    At any rate, at our present state of engineering and technology, a fossil fuel engine and a mechanical reduction gear/Prop are the most efficient means of propulsion we have. If you dont include sails! Even that aint free!
     
  5. marshmat
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    marshmat Senior Member

    Fred,

    If I read correctly, you're advocating the use of a larger prop at lower RPM, but rather than gearing the engine down, you're suggesting that its redline should be detuned slightly?

    Seems to make sense; after all, a prop sized to absorb the full power of the engine at WOT will usually be underloading it by a fair bit at 2/3 throttle. Provided, that is, you don't need WOT.... but with the more efficient large-diameter prop, one should be able to maintain thrust reasonably well when beating into the wind.

    With a modern computerized engine I would think some tweaking of the computer would be called for, even if just to change the rev limiter....

    Kind of makes me wonder about truckers. At the rest stations along Hwy. 401, they're always griping about the high cost of diesel. Then they park in the back and leave their 400-hp Cummins running for nine hours, spinning a pair of alternators and an A/C unit that draw maybe 15 hp combined. Then they complain about the dismal fuel economy their rig is showing and how often it has to go to the shop.
     
  6. SFcruiser
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    SFcruiser Junior Member

    DC safety - all-in-one myth

    Back to the DC system, high voltage DC is very deadly - 140VDC is more dangerous than 240VAC. I just don't like the idea of pushing all of these high voltage wires around my cruising boat to achieve a goal of "all-in-one". Bad idea!

    Safety standard, such as IEC60950, regulates DC voltage lower than 60V as "separated extra low voltage (SELV)" and subject with less regulations. Telephone system or Golf car has been using 48VDC for many years. If its for the after-market re-power usage, 48V or 60V DC motor is good target. If we consider 100 amp of current as upper limit due to the size/cost of wires and motor, these motors will have a power less than 10-15hp so the targeted market will be limited - again, this is the safety consideration for the after market installation.

    If its a well-thought-off arrangement such as a motor/generator set-up, I would consider 140VDC but still put a big dangerous / expert only sign on it. If the goal is using 140VDC on all the appliances, I will throw the plan out of the window today and say "Bad idea!". Who want to own a boat with expert-access-only sign everywhere? Remember these set-up should be use for 10-20 years - following the life span of a diesel engine. Would you put your life on the chance of a puddle of 10-years-old epoxy barrier coating? :mad:

    140VDC refrigerator/stove/winch/windlass/water-maker are expensive or not-readily-available. As a result, you still need a big DC-DC converter or DC-AC inverter to achieve the goal - which kill your efficiency. From economic / availability point of view, a 24VDC / 120VAC system is probably still a better choice, cheaper generator and plenty of appliances to choice from - then, we are talking about a separate generator again ... :confused:

    So, again, I found its very attractive to install a electric motor on daysailor / club racer up to about 36' - at least that is a viable option. Grid power is cheap and clean. Honda portable generator is quite and efficient - I need it at home too. For other applications, there are still a long way to go.

    SF cruiser
     
  7. masalai
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    masalai masalai

    SFcruiser - All high vlotage stuff can be dangerous if one foolishly sticks ones finger or other things where they should not be.... Choices remain restricted to available technology - - I would regard 240v ac as less dangerous than the US system using 110 volts AC as the amperage and evidence of showering sparks in "colliding overhead wiring is quite alarming to view - - - mostly here in OZ (I am not an electrician but observe stuff) the supply shuts off when there is a short detected (live wires may fall down and not short sufficiently to cause auto-shut-off)....

    It is not difficult to convert 240 v AC to DC and vice versa as can also be done with 120 or 140 volts and a knowledgeable and competent QUALIFIED electrician should be able to design and build such a device and put it in a box for "safety".... from stupidity - but none can protect the ignorant stupidity of some.... 24 V or 48 V power leads are very thick and heavy and expensive.....
     
  8. SFcruiser
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    SFcruiser Junior Member

    Yes, DC at higher voltage IS more dangerous than AC at the same voltage: I am not an electrician but I am a PhD EE with many many years of experience in the lab. The reason is: DC voltage is more efficient to penetrate the body and give it a shock. It also delivery higher energy to create damage than a AC current at the same voltage.

    AC can be converted to DC - same as the other way around. However, you will loss about 10-20% of energy. Its OK if its a low wattage application. It is bad if its a high-output application - create lots of heat.

    Marine environment is bad for this kind of set-up. You have condensation at cold area; you might have a leaking sea water tube. These recreational boat usually have a life longer than 20 years and boaters like to do stupid things on their boat..... If anything happen to create a path for the 140VDC, you might get a shock at some unexpected places - might not need to stick your finger to the electrode. This is more dangerous than carrying gas tank on board which many people say No.

    On the other hand, if the 140VDC leak thru the sea water, you might get some salmon belly up around your boat ready to be served as dinner! :p Just a joke.
     
  9. Ratch
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    Ratch Junior Member

    Hi SF,

    My understanding is a little bit different. I was taught that electricity causes muscles to contract so there is a real danger that you get a death grip on the live object and cannot let go. The advantage with AC over DC is that because AC changes polarity your muscles will spasm rather than just contract so there is a chance you may be thrown free of the live area.
     
    Last edited: Dec 12, 2008
  10. thudpucker
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    thudpucker Senior Member

    Back in the 60's somebody realized this Electricity/Wet wood/metal/etc was dangerous to the casual dummy who just might touch something hot(live)

    I went around to customer sites for a year installing the Cord with the third (green) wire in it and advised the customer to get the 3-pronged sockets etc. You guys all know about that stuff now, but then, only a few did.

    I'd get calls from my customers saying "your Till shockes me" and invariably it'd be something else sitting on the Stainless bar, or the wet Wooden bar.
    The Till is grounded, the 'other' device was leaking to a ground.
    When the Customer leaned against the bar and touched my grounded Till, she became a path to ground.
    Whoo hoo! What the hell was that? And all of a sudden nobody wanted to work the Till. Ignorance yes, but deadly too.

    So we are talking about installing some AC generators to provide some big Black Rats to run a treadmill. Whatever we have that uses the Electrical power can also leak.
    I think its foolish for a non-EE to even discuss this option. It's absolutly dangerous, and you just cannot ever tell in advance when something is going to use you as a 'third path to ground' and when you notice, its often too late.

    SFcruiser is the PHD, I'm just an AA, so he's gonna have the last word.
    But before any of you actually try this in a boat, a wet conductive enviroment, you better make sure your work is reviewd by an experienced EE.
    A failure could be a downright shocking experience!
     
  11. SFcruiser
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    SFcruiser Junior Member

    I should say that there is no perfect way to build a perfect boat - its all trade-off. Although I do not like the idea of using high voltage DC in the marine environment, this is actually "my preference". People would push the way they like. This is also the drive of new technology. I am in general very interested about all the development on P/E but I do worry about the safety factor for a cruising boat.

    The new Lithium technology is there but its still very expensive. I found that many of these advanced battery factories is at China instead of in the US. This is really strange since US usually is the technology leader till volume production.

    I found and watched a DVD named "Who killed the electric car". It is a great documentary to tell the story behind the secne. Might provide some suggestions on the above question.
     
  12. FAST FRED
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    FAST FRED Senior Member

    "you're suggesting that the diesel redline should be detuned slightly?"

    No, All diesels are most efficient at HEAVY load , the problem is when set to mfg spec say 125hp at full tilt , the engine is severly underloaded at a 1600 rpm cruise of 2 gph , perhaps 35hp.

    So a larger diameter prop is used to ask 35 hp at an rpm that can create 45 or so. THis may cut the fuel consumption in half.

    The truckers using the 550hp to keep warm is now illegal in most states , and APU (what we call gensets) is used to keep cool or warm. Uncle Sam gives them an uncounted 400lbs on the max truck weight.

    If battery tech ever gets 1000% better the electric boat dream , might become more than mental ************ , for folks with almost no hotel loads.

    FF
     
  13. SFcruiser
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    SFcruiser Junior Member

    Lithium Battery (LFPO) comparison

    I collected some data about Lithium batteries. Batteries with LiFePO4 chemistry seems promising - longer lasting without fire danger. You must have a battery management system (BMS) to handle charging / discharging to extend the battery life.

    Here is a bulk-park comparison with the normal AGM battery:

    Price: ~ 2.5-3 times higher than AGM (BMS included)
    Weight: ~ half of the weight of AGM
    Volume: ~ 40% saving in volume.
    Cycle life: ~ 2-3 times longer if managed properly
    (>2000 cycles at 80% discharge)
    Comparable cranking amp and capacity.

    It might make sense to use this system for certain P/E applications. Expect a 144VDC 200ah battery set costs $18-20k (weighted at ~ 600lb)

    :)

    SFcruiser
     
  14. masalai
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    masalai masalai

    I'd rather a mast and sail at this point in time:D:D:D
     

  15. brian eiland
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    brian eiland Senior Member

    Perhaps you would like to make some contributions to this subject thread??
    http://www.boatdesign.net/forums/boat-design/batteries-new-battery-technologies-21869.html
     
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