Need help with electric boat modification planning, rough estimation on engine and battery capacity

Discussion in 'Boat Design' started by xellz, Jul 2, 2017.

  1. xellz
    Joined: Jul 2017
    Posts: 19
    Likes: 2, Points: 3
    Location: Japan

    xellz Junior Member

    First short introduction. I'm currently living in Japan on a small island of volcanic origin with amazing fishing grounds around. Recently i got boat license, so now i'm looking for options. Main purpose for boat will be fishing, i.e. need efficient vessel, speed isn't priority. I read quite a bit about downsides and benefits of electric boats and if possible i would really like to go with fully electric.

    What i can't do right now is roughly estimate the cost to move forward with planning, there is some financial help from local fisherman association and i need numbers to show. My budget also has a limit.

    Boat type and size, hull will be from one of old boats that can be bought here fairly cheaply. Smallest boat that is still comfortable to navigate around island is something like Yamaha DX-27 (if google for images add boat or ship :)) Dimensions of yamaha DX-27 are 8.23m*2.15m*0.99m, tonnage 1.5t
    With 103kw engine cruising speed supposed to be around 25knots, i'm aiming for about 10knots cruising and top speed about 13-15knots for emergency. I once saw this boat with 42hp engine which stated exactly this speed. And similar output electric engine would be around 15kw?

    I really need rough estimation on engine power and if possible some links to recommended companies. I did search, but price variation and parameters vary quite a bit.

    For now i need to answer this:

    1. Electric engine power and rough pricing on it
    2. Battery capacity needed for full day out. I.e. top speed for 5-6h (i certainly understand, that most likely won't be using that much due to really slow speeds during fishing, but extra juice is necessary for safety). This including capacity drop during years of use, i think drop in capacity to 80% from new would be good start.
    3. Control box, here simply no clue on where to start.


    I won't be assembling or repairing it myself, helping or which is most likely, stay away and don't get in the way of more skilled people :)
     
    Heimfried likes this.
  2. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    I guess this points will not fit in a viable solution. The crucial issue is the battery. To feed a 15 kW electric motor a day long including emergency reserve means a very expensive lithium batterie bank. If you go for cheaper lead batteries instead, the increased displacement will eat up the advantages, because you need more power.
    I've started to build a electric motor kat right now and decided only to go slowly with that boat because of this reasons.

    May be, someone else will open a more optimistic view for your plans..
     
  3. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Unfortunately, I agree with Heimfried. The only way, you may have a chance to move your 1500kg motorboat is with lots of flexible solar panels on a very light roof construction. Something like 18 x panels of 250 watt Swiss or Dutch made panels. (reasonable expensive) Then a cheap hobby type Lithium battery 20.000 mAh and 14.8 Volt @ 105 Dollar ex China placed parallel and in serial to obtain the correct voltage. A company in the far East is also considering making a similar boat, but they are at present evaluating the risk. They working at 72 Volt (6 x 12 Volt panels and batteries) and that means the open voltage of their solar panels is 6 x 30 = 180 Volt. In Direct Current, it means instantaneous dead , if you like to work in seawater environment when you have a problem. You heart can only handle 20 mA and then it is good bay to you. O.K , O.K you may have insulated every connection, but one day you have a problem you have to solve and most people are not qualified or has the knowledge to take special precaution.

    My advice is for you not to go over 36 Volt motor. This means you cannot go over the 6 to 8 Kw motor, otherwise your copper becomes so heavy and not practical. You could use thick copper welding cable, but you need to tin the ends and afterwards seal it with liquid insulation. The reason why you should not go over the 36 Volt is a simple one. explained in the previous sentence.

    6 Kw at 36 Volt means 170 Ampere and 8 KW , 220 Ampere. Your switching becomes a nightmare, you fuse will be a problem. But it can be done, if you have some knowledgeable people helping you. Cost ??

    Your Lead acid batteries are at least 600 Kg, goodbye to your speed you are hoping for. No 6 x 20.000 mAh Lithium cheap hobby batteries parallel and 3 x in series (total 18 batteries) = 44 Volt and 5.280 Kwh at a cost of ex China 1890 USA dollars. Then 18 flexible solar panels at Euro 400 each = Euro 7200, maybe you can negotiate a better price from the Swiss manufacturer. Just google "flexible solar panels" .

    Your motor, if you are lucky maybe you can find a 6 kw , 40 Volt for USA 500 dollar, and your MPPT regulator from a company in Port Elisabeth< South Africa and a controller to regulate your speed for 300 USA dollar , but you real problem will be to make or find a battery charger to charge your Lithium batteries when you were unlucky to have your batteries depleted.

    Yes, it can be done, but it will not be easy. With a 6 Kw motor you will only be able to do 6,5 knots with a 8.23 meter , 1500 kg boat like you have in mind.
    Good luck
    Bert
     
  4. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    15kw is not equivalent of 40+ hp. That lie comes from faulty marketing of e-motor manufacturers.
    15kw e-motor is 20hp gas equivalent assuming that the kW for e-motor is shaft power. Often it is actually the power intake which means that the actual shaft power is fair bit (15-20%?) less.

    With e-power you have to be very optimal in setup. That means that your battery capacity needs to match typical need and ample reserve just can't be had (pointless to carry great amount of extra weight, just in case).
    Same for speed, pick speed that is lowest you can live with and accept that you cannot go much beyond it.

    Power and boat shape (and weight) requirements are drastically different at 10 knotts and 20. In fact drop a few knotts and the plan will be much more feasible.
     
  5. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

  6. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    I agree with your statement that 1 horse power shaft power is one electric horse shaft power and nothing more. The funny thing is that your countryman at OceanVolt publicly has it on their website. They should actual say it different. A Brushless motor has basically the full torque at a few revolutions. With a diesel or petrol, it has to be achieved with reductions or slip clutches. That means efficiency is better with electric motors. (If 10 Hp electric is compared with 10 Hp diesel/petrol) Bert
     
  7. kerosene
    Joined: Jul 2006
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    Location: finland

    kerosene Senior Member

    At what boat speed? When does a prop shaft require high torque at low rpm? What is the efficiency of electric drivelune at lets say 100 rpm? 500 rpm?
     
  8. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Electric is a desirable option but the reality of current (no pun intended) equipment makes the prospect of using electric systems for such a boat, more than merely problematic.

    A more practical solution is to use a nice little Kubota or Isuzu diesel or Subaru gas engine. Pound for pound either is more powerful than an electric system, and also quite reliable.
     
  9. xellz
    Joined: Jul 2017
    Posts: 19
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    Location: Japan

    xellz Junior Member

    Thanks for replies, especially about hp conversion myth, this changes things quite a bit. But still idea doesn't look hopeless yet.

    Budget for battery pack alone would be around 30.000-40.000$, depends on total package and advantages of electric might can push little bit more. Maybe lower cruise speed or something else can help achieve goal. I saw first fully electric fishing boat news from Norway and that it can operate full working day (10h) on single charge, i.e. energy density does allow this. Aside from money side, it's not impossible.

    There are 2 main reasons i'm looking for electric conversion. First one is maintenance and exploitation costs, i'm living on island and ferry comes 2-4 times a week only. Repair costs if anything happens, are more than double the usual and Japan pricing to begin with is rather high, fuel has to be carried in drum cans and costs extra. Majority of time boat will be in idle, i.e. diesel engine would consume fair bit more. New, not used boat from Yamaha is rather expensive, used one can come with various surprises that for a beginner can cost a lot.
    Second reason, uniqueness of this boat can help achieve higher profits. It will be used for commercial fishing and small, 1-3 ppl group sports fishing. Fully electric certainly will stand out above the rest. Inconvenient place for fishermen, but expensive types of fish more or less cancel it out, main target species sold for ~20$ per kg and usual size is 5-10kg. And something like a single fish sold for 5000$ also exist, jackpot, but last active fisherman (main income, not for fun or food only) does catch at least 1-3 per year, not as big, but close.
     
    Last edited: Jul 3, 2017
  10. xellz
    Joined: Jul 2017
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    Location: Japan

    xellz Junior Member

    Ok, good advice for max voltage, i will try to plan without going over 36v. When i was looking for engine options i saw somewhere an option where up to 3 engines could be joined in parallel, almost like lego piece. I.e. 2x 6kw units could output 12kw in total to main shaft. Right now i can't find the link. Low speed isn't a problem here most of the time, fishing location, scenery viwing is rather close. Trip around the island would be about 17-18km, most fishing locations are within 10-12km from port. Extra torque is for sudden weather changes and strong current locations. Less than 1km, but in high tide current speed can reach up to 5knots. Most locations i was fine even in a pedal driven hobbie kayak, but had to avoid most interesting places exactly because of too strong tide current and if wind changes direction, waves would become really nasty.
     
  11. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    As most motors in the 6-8kw range have shaft ends on both sides it is very easy to construct a power unit with two motors. For normal operation either one can do the job, in bad weather and high seas you use both. An advantage is that you can switch over to a fully charged battery bank when the one in use gets tired.
    I once had a sports car with two equal fuel tanks. When the low fuel warning light came on, a flip of the switch enabled the other tank and the gauge showed full again.
     
    BertKu likes this.
  12. xellz
    Joined: Jul 2017
    Posts: 19
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    Location: Japan

    xellz Junior Member

    Thanks for input, this might be a good idea actually, as it adds extra level of safety too. Compared to a combustion engine electric motor might be more simple and less chance of failure, but it still can break. With second motor it would be possible to return without much trouble.
     
  13. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Junior Member

    Xellz, what you want might be possible under the conditions described, but not how you imagine it.

    First and most important thing is the boat. Forget about any planing hulls (the yamaha type) what you need is a displacement hull optimised for low power operation. This means something long and skinny with a round bottom and not immersed stern. 15kn top speed is out of the question for a monohull, plan for something like 9kn for a 15m hull or use a catamaran. So basicly it boils down to low speed monohull or catamaran.

    For a motor, controller and charger you need to speak to someone that sells and repairs electric forklifts. 48V instalations are common, you can use their expertise and second hand parts.

    Batteries and pricing are a local thing. In the EU, 4000 USD would buy you around 9kW of chinese prismatic LiFePo4, or 38kW flooded lead acid (nominal power not usable). You need to research japanese prices, there is no other way. For flooded lead acid ask the forklift guy. Lithium will need a BMS and both systems will need a dedicated charger. Your dock will also need an electrical connection big enough to recharge overnight. Another option would be to find a battery from a wrecked electric car like the Nissan Leaf. Go to DIY Electric Car Forums Site Home http://www.diyelectriccar.com to learn about that option (not plug and play, not easy) and related topics.
    How much battery you need and what type is highly dependent on chosen hull, power installed, duration of the desired top speed and average consumption.

    If I were in your place with your problems I would look at the sail option. A traditional fishing type sailboat with a small diesel, gas outboard or electric for manoevering and motorsailing will probably cover all of your problems. So the question is what was used for fishing in your area 70 years ago, and are there any of those hulls still around? If not you may have to look for a suitable conversion candidate or building a new one.
     
  14. xellz
    Joined: Jul 2017
    Posts: 19
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    Location: Japan

    xellz Junior Member

    My bad, i missed one zero in usd. I got used to yen already too much :) 30.000-40.000 usd for battery pack at most. I see one of local sources has 3.8kw, 40kg and 3000 cycle units for ~3000usd. If search a bit more or try to get a discount for "bulk" order, perhaps can aim for ~50kw LiFePo4.

    Yamaha boat was a bad example indeed, but size is about what i would like to use myself. Also thought that deep v might be better for high waves that are fairly common here. I'm still not too used to speed on boats so might actually wanted too much from the beginning. 7-8knots might be more than enough.

    It will take quite a while to take off this project, that's why preparing early and searching for points missed. Already learned quite a lot of new useful information. For at least half a year i will be practicing on one of local boats, to get used to operating 8-10m long ships.
     

  15. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    If you can show me a diesel or petrol engine which can run at 10 rpm and supply the full power to the propeller, without reduction boxes or slipping clutch, I will come to Finland and buy you a beer. What about that one. Bert
     
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