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Thread: Electric inboard for 7 ton boat

  1. #1
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    Default Electric inboard for 7 ton boat

    Anyone had any experience building up an electric inboard kit for their boats without using a kit from someone like Electric Yacht, or Thunderstruck?

  2. #2
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    Default Re: Electric inboard for 7 ton boat

    Well, WB magazine once had an article touting the benefits of an electric inboard installed on a classic boat. I corresponded with the author who conceded that it wasn't good for much more than maneuvering in and out of the slip in the harbor. It didn't have the power, nor the battery capacity, to really serve as an internal combustion engine would in open water and for any distance. Your mileage may vary, but they seem a lot of money for not a lot of bang for your buck. It's not just the size of the boat that determines how much electric motor you need, but also the nature of the water you are going to be using it in. If you are going to run on a calm lake, that's one thing. If you are going to be bucking six knot tides or thirty-five knot winds trying to get out of the way of that super tanker that's continuously sounding its horn and bearing down on you in the shipping lanes (as on SF Bay, for example,) you're going to need a whole lot of electric motor! The highly efficient motors used in the commercially sold set ups aren't cheap, nor are the battery systems. I don't know that you'd save much trying to do it yourself. A hybrid may be do-able, (Think a "lunch box" generator with a table saw motor plugged into it?) but you're right back where you started from with an internal combustion generator. That system works well with big diesel engines and electric motors on tug boats, but on a seven ton sailboat, you'd probably be better off going with a standard internal combustion kicker like everybody else has. There's usually a reason when everybody is doing something the same way, ya know?
    Last edited by Bob Cleek; 03-09-2017 at 04:19 PM.

  3. #3
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    Default Re: Electric inboard for 7 ton boat

    I saw that article. I am not surprised that he had limited usage. One of the things that really struck me is that his battery bank is really small. Less than half the usable capacity of what most folks who put the kits together suggest. Thankfully I don't sail in SF Bay anymore, and anyone bucking a 6 knot tide in a 30 foot sailboat needs to read the tide tables more carefully.
    I've been using a 7 hp outboard since I pulled the fickle diesel, and its fine so long as there's not big chop.

  4. #4
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    Default Re: Electric inboard for 7 ton boat

    Check out some of the hobbie electric car magazines. That area of electrification is more popular and so there tend to be more options.

    All electric can make sense in a boat in calm waters (SF bay and central pacific are my home waters and I agree with all the above) especially when the batteries double as ballast. Motors and controllers are easy to come by and not all that expensive, but it's the batteries that have a long way to go.

    The other thing to keep in mind is that depending on the battery technology you use, it is not a low maintenance solution. If you use lead acid batteries (still the best bang for the buck) you have to stay on top of them to get the longest life. The so called zero maintanance chargers are anything but that, not to mention adding water, keeping them clean, and maintaining low resistance connections.

    When I last did the math the electric solution never broke even with the diesel. For a J24 it was looking like $20k to get something equivalent to an inboard.

  5. #5
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    Post Re: Electric inboard for 7 ton boat

    If I bought a pre-built kit it would be more expensive than have a new diesel installed at a yard. However, I am a pretty handy guy and my dad has built an electric car from scratch so I think I may be able to save on labor and parts.

    Prebuilt kit $6k
    Lipo battery pack + charger $4-8k
    Fancy charger & monitoring system $2-3k

    DIY kit with similar specs, but no polish $3k
    Battery bank price cost is basically the same

    We will see what I am able to work up from whats on hand.

  6. #6
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    Default Re: Electric inboard for 7 ton boat

    I recently did a feasability study on an electric powered boat. All of the companies i spoke to were adamant that there systems were the best, but could not back up any of their claims to endurance under use, maybe like a car manufacturer giving expected mpg figures being different in real use. The conclusion for this particular boat and its use was a hybrid unit, smaller battery bank than all electric, but with a small diesel as generator AND propulsion. Not a cheap package, but did allow for a projected low speed cruising of around 6 hours out of 24. Service life of the Li-Po batteries were around 18months in a continous duty cycle, and given the cost of the battery bank, did not provide a benefit over running the diesel for the same amount of hours.
    For still waters, or getting in and out of a harbour in areas of reliable wind, it can be an option, but in areas of strong tidal streams and variable weather, not what i would call a reliable form of back up power, the same could be said the same of a craft fitted with an inboard diesel, but with only a tiny tank to give a few hours power. May suit some users, certainly not all.
    I also get a bit miffed that a lot of these suppliers sell their project as being "green", when they dont seem to accept the damage done mining for rare earth metals for modern battery systems. I would certainly like to put a hybrid package through long term use, i expect the time spent maintaining the battery packs in good order, even if done through smart -chargers, would require more observation and control than regular fuel filter swaps to keep a diesel running.

  7. #7
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    Default Re: Electric inboard for 7 ton boat

    Looked at electric for my Rambler. With the 8' tides and currents we have wasn't practical. You can make the power no problem. Endurance is an issue.
    The tech works great in cars where the continuous power requirements are lower.
    For in and out of the slip on a sailboat it works well.
    Fight Entropy, build a wooden boat!

  8. #8
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    Default Re: Electric inboard for 7 ton boat

    Yes, it all comes down to the batteries. I have a friend that worked in design at Tesla motors. He Said the majority of those R&D dollars were spent trying to design a system that would not damage the batteries or let them catch on fire.

    Contrary to popular belief Boeing still has not solved the fire problems on the dreamliner.

    Lithium-|fill in the blank| has the potential to make this practical technology for boats, but understanding of the batteries is still very low. As a result Tesla charges and triple monitors every single cell! What's not going to be practical for most diy projects.

  9. #9
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    Default Re: Electric inboard for 7 ton boat

    Yes, it all comes down to the batteries. I have a friend that worked in design at Tesla motors. He said the majority (70%) of their R&D dollars were spent trying to design a system that would not damage the batteries or let them catch on fire. The rest of the car was designed using the final 30% .

    Contrary to popular belief Boeing still has not solved the fire problems on the Dreamliner.

    Lithium-|fill in the blank| has the potential to make this practical technology for boats, but understanding of the batteries is still very low. As a result Tesla charges and monitors every single cell! That's not going to be practical for most diy projects.

    I wonder what the car conversion kits do to keep the batteries safe?
    Last edited by leop; 03-10-2017 at 06:03 PM.

  10. #10
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    Default Re: Electric inboard for 7 ton boat

    Quote Originally Posted by McKee View Post
    If I bought a pre-built kit it would be more expensive than have a new diesel installed at a yard. However, I am a pretty handy guy and my dad has built an electric car from scratch so I think I may be able to save on labor and parts.

    Prebuilt kit $6k
    Lipo battery pack + charger $4-8k
    Fancy charger & monitoring system $2-3k

    DIY kit with similar specs, but no polish $3k
    Battery bank price cost is basically the same

    We will see what I am able to work up from whats on hand.
    Well then yes, you could do it much cheaper.

    Don't underestimate the work involved in keeping the lipos safe.
    Many a camper has been burned down charging a few AAs too fast. You would have a lot more potential energy than that aboard, and the pounding that boats take makes the chance of a lipo meltdown that much more likely. You don't even need to be charging them to have go off.

    So are you going to try? Sounds like a fun project.

  11. #11
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    Default Re: Electric inboard for 7 ton boat

    If something for quiet maneuvering in and out of a slip or small harbor is all that's wanted, I think a Torqueedo Cruise outboard would be a good solution. If being green is what's desired, I think a small diesel auxiliary or outboard would be the better way to go. Reclaiming all the embedded energy costs for an electric drive system would require a ton of use over a consistent distance. Might work for a water taxi with charging between runs, but not much else with current tech. If quiet motoring is wanted and cost and being "green" don't matter, electric inboard might make sense, but will still be $. Another exception I can imagine would be a solar catamaran, light and covered in solar panels. Wouldn't need many batteries because they'd just be a capacitor, effectively. Speed would be dependent on sun. Of course, the greenest thing would be an oar or yuloh or tow.

  12. #12
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    Default Re: Electric inboard for 7 ton boat

    Ian McCoglin, did you once state the equivalence between a gallon of gas and a pound of lead acid battery? Or another way, for one hp-hour of power, how many gallons of gas would be needed vs how many pounds of lead acid battery?

  13. #13
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    Default Re: Electric inboard for 7 ton boat

    I'm using LiFePO4 batteries in a small setup for a 20' Elver. The set consists of 8 100ah CALB cells. They power an 80 lb thrust trolling motor. LiFePO4 is much safer than most other flavors of lithium in that it won't catch fire when the cells are damaged. There's plenty of Youtubes showing destructive testing of these cells. As for monitoring each cell it is absolutely necessary since lithium cells don't tolerate over discharge and they don't self balance like a lead acid battery does. My setup has solar cells so it should be good for general use in calm waters. Testing will tell.

    My understanding is that the Tesla has about 8000 of the little 18650 cells. They can catch fire.


    For my larger boat I briefly thought about replacing the dead diesel with electric but I knew it would not work for anything like cruising to Chattanooga so I decided on a new diesel. In the past I looked at steam but realized that it is much less efficient than diesels. I also looked at stirling but realized that there just aren't that many useful stirling engines in the size that I needed on the market. Each year I use maybe $50 worth of diesel. The maintenance spares cost more than that each year.

    As for making diesel green I could plant a grove of olive trees and press olives for the olive oil. Then I would have to transform it into bio diesel. I would be green though.
    Will

  14. #14
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    Default Re: Electric inboard for 7 ton boat

    Glad I found this thread... I've been looking at an all electric or hybrid-electric drive on a St Pierre dory. Was going to base it off the Elco system or kit it out myself with solar and a 2kw jenny for backup power. After seeing the cost analysis I'll probably just kit it out myself... Fortunately the Navy has taught me all that electronical stuff so figuring it out should be easy. (enter Murphy...)

  15. #15
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    Default Re: Electric inboard for 7 ton boat

    Well, I've built my 7.75 ton Kahuna cutter http://www.smaalders.net/yacht_design/ and installed the kit from Electric Yacht http://electricyacht.com/product/ele...ug-n-play-2-2/ . Unfortunately, I haven't been able to test the system yet. Outfitting the boat has been a bigger drain on the wallet in a shorter amount of time than building it was. Because of that, Susan and I are currently away from the boat rebuilding our kitty. In addition to paying off some bills that allow us to be free for cruising, we are saving up for the batteries. I do not plan to use Lithium for now, instead out intent is to use AGMs... 8 6vt, 400mah for the 48 volt system.
    I don't have any illusion about the capability of this system (I hope). When I first started building, my intent was to go engineless. To get Susan onboard, she wanted an engine. I put my foot down on the washer and dryer combo. I definitely didn't want a deisel due to the odor and oil since we live aboard. I plan to use the system minimally for maneuvering around an anchorage or in and out of marinas. I'll be happy if I can get 40 miles or so motoring down the ICW between charges. Along with shore-power, I have a Honda eu-2000. Solar or wind are potentials. I've taken a few sails on a converted friendship sloop using the same system http://www.sailmuscongus.com/

    Should have answers by august.
    Last edited by scottmacc; 03-15-2017 at 01:16 PM.

  16. #16
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    Default Re: Electric inboard for 7 ton boat

    Beautiful boat, congrats on getting into the water. What part of outfitting are you stalled at?
    Given the similarities in our boats I look forward to hearing how the system does once you get a change to use it.

  17. #17
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    Default Re: Electric inboard for 7 ton boat

    The Batteries are the biggest item.... roughly $5,000 if I go AGM. This break we took was mostly to pay-off the credit cards. Mast and boom are built but un-stepped. I do have all the standing rigging. I need the running rigging. I'm hoping to do that during a two-week vacation I have scheduled in April. Working sails are made. I brought my sewing machine on this job with me so sail covers are completed. Need to purchase anchors and rode but with everyone switching over to the latest and greatest, CQRs and Bruces can be found relatively cheaply for now. That's really all I need to go sailing, but there's always another list...pressurized hot water system and A/C for when at the dock to keep Susan comfortable.

  18. #18
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    Default Re: Electric inboard for 7 ton boat

    Batteries are pricey. I am planning 3 years out for my re-power so I can afford the lithium battery pack. I'd go AGMs but I can't afford the weight. I've been looking at all the electric inboard kits out there and they are nearly identical component wise. I am planning of building it up piece by piece which helps make the price tag of the battery pack easier to stomach.

  19. #19
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    Default Re: Electric inboard for 7 ton boat

    I'll be very interested to see how your system works out. 40 miles sounds awfully optimistic to me. I'd baby those AGM batteries. Our house bank averaged about 3 years on our Lifeline AGMs living aboard. We usually had no solar or shore power, so they only got a full charge 1-2 times a month and equalization was almost unheard of. Even with our starter battery (also a Concorde AGM,) 5-6 years has been the max despite staying almost fully charged and having yearly equalizations. 3-5 years on AGM batteries seems a fairly average lifespan talking to other cruisers. Alas, almost all the battery tech available on a sailboat comes with drawbacks, whether it be Flooded LA, AGM, Gel, Carbon Foam AGM, or LiFePO4. I don't think there's a best solution, but do baby those AGM's if you can. They'll love marina stays more than you do.

  20. #20
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    Default Re: Electric inboard for 7 ton boat

    Battery tech is moving forward. Not as fast as we'd like but it is now recognized as a major hurdle to technological and environmental progress. That means resources are being put into solving the problems associated with it. I don't anticipate needing to buy batteries for my build for another 20 years or so. Retirement project. I am cautiously optimistic that there will be a suitable solution at a reasonable cost by the time I anticipate needing them. In the meantime, I plan to put two externally mounted fixed thrusters to have a twin screw sailing vessel with large slow turning screws. Most of the regenerative crowd have trouble getting their regenerative systems to regenerate under sail. I believe this is due to the small screw size. And the screws used are optimized for propulsion. I intend on using large screws and optimize them to be more balanced between propulsion and regeneration. 20 years is lots of time for the tech to catch up to what I want and really, the only part missing at this point is decent batteries. Here's to hoping. Good luck solving your issues today, I know it will be challenging.
    If one advances confidently in the direction of his dreams, and endeavors to live the life which he has imagined, he will meet with a success unexpected in common hours.
    -Henry David Thoreau-

  21. #21
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    Default Re: Electric inboard for 7 ton boat

    Quote Originally Posted by scottmacc View Post
    Well, I've built my 7.75 ton Kahuna cutter http://www.smaalders.net/yacht_design/ and installed the kit from Electric Yacht http://electricyacht.com/product/ele...ug-n-play-2-2/ . Unfortunately, I haven't been able to test the system yet. Outfitting the boat has been a bigger drain on the wallet in a shorter amount of time than building it was. Because of that, Susan and I are currently away from the boat rebuilding our kitty. In addition to paying off some bills that allow us to be free for cruising, we are saving up for the batteries. I do not plan to use Lithium for now, instead out intent is to use AGMs... 8 6vt, 400mah for the 48 volt system.
    I don't have any illusion about the capability of this system (I hope). When I first started building, my intent was to go engineless. To get Susan onboard, she wanted an engine. I put my foot down on the washer and dryer combo. I definitely didn't want a deisel due to the odor and oil since we live aboard. I plan to use the system minimally for maneuvering around an anchorage or in and out of marinas. I'll be happy if I can get 40 miles or so motoring down the ICW between charges. Along with shore-power, I have a Honda eu-2000. Solar or wind are potentials. I've taken a few sails on a converted friendship sloop using the same system http://www.sailmuscongus.com/

    Should have answers by august.

    Hopefully that is a typo and you meant 400 AmpHour, rather than 400 milliAmpHour. The first is an L16 sized battery while the other is about the right size to go in a pocket camera :-)

    The AGM 400Ahr rating is based on a 10 hour discharge rate, which means you need to limit your sustained load to 40 Amps. If you can actually maintain hull speed at 40 Amps load, then yes you can expect to get 40 miles in about 5 hours between recharges, while draining the battery bank to around 50%. You don't want to be discharging the batteries any deeper than that when they are new. As the batteries age, the depth of discharge will naturally increase for the same load and duration. If 40 Amps will only sustain 4 knots, then trying to go any farther than about 20 miles between recharges will result in a reduced life for your batteries.

    regards,
    Joe
    These days, everything I do is just "puttering around"

  22. #22
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    Default Re: Electric inboard for 7 ton boat

    I agree that the electric boat industry is growing amazingly fast. Having spent time in the US Submarine Service has made me wonder why it has taken so long to make electric power for boat owners an affordable and efficent choice in lieu of a reciprocating engine. I just watched an ad for a rudder mounted motor that is available from Duffy Marine. It will allow a vessel to turn so tight as to chase it's own tail!
    Jay
    http://www.duffyboats.com/power-rudder/

  23. #23
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    Default Re: Electric inboard for 7 ton boat

    Well, 20 years will do a lot for battery tech, no doubt. The economics may be quite different then. The idea of having 2 large screws on a sailing boat would probably cripple it's sailing performance, though, no? Much like a prop cage. Also, would catch lobster pots real good. When it comes to generation, I've always thought that a removable system had some real pluses. The towed generators make pretty good power (roughly 12W per knot,) and perhaps a transom mounted cross between a torqueedo and sail-gen (http://eclectic-energy.co.uk/product-category/sailgen/) could give the best of all worlds. Directional thrust, generation when sailing near hull speed, zero drag in light airs, etc. Likely 20 years will do a lot for propulsion and generation options too.

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