Choice of electric motors as inboards for a catamaran

Discussion in 'Electric Propulsion' started by xellz, Jul 16, 2017.

  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Electric fencing is not a relevant, nor precise example, and the sarcasm was from the other fellow.
     
  2. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi fallguy , I am inclined to agree with you, except on one point. It all started when I gave the warning, that should people go for electrics and special with higher powers, using for that reason probably exceeding 50 Volt DC power source, that it is extreme dangerous on a boat with salt water and bare wet hands, without removing the plus from the battery bank, or having warnings labels at critical points. Unfortunately that is my professional opinion for people who like to start playing with electric motors. Bert
     
  3. xellz
    Joined: Jul 2017
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    xellz Senior Member

    I didn't give up idea of electric propulsion, however i need to do it right or i will end up with an expensive toy. Funds and lack of skills main problem now. This idea started with partial funding in mind, up to half of total cost with some additional help. I don't have sufficient skills to design and safely assemble electric propulsion for a large boat on my own, so i rather go with ice outboards than risk failing entire project or even endangering my own or someones life. Right now i will focus on getting catamaran on the water with minimal required equipment. After boat on the water can be certain on how much money left and continue from there. But at the very least i think this system has to be professionally designed.
     
  4. dsigned
    Joined: Aug 2017
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    dsigned O.R.C. Hunter

    Not sure if this has been mentioned yet, but here's a guy who is refitting an old Wharram with solar/electric as the non-wind propulsion.



    I believe that's the link to where he discusses power options. I think he wound up going with something along the lines of 20kw brushless motors. He's not up and running yet, so his opinion may need to be taken with a grain of salt.
     
  5. gzs
    Joined: May 2018
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    Location: Germany

    gzs Junior Member

    Xellz, I'm very much intereted in an electric catamaran aswell. I would use it for commercial purposes. Because of the battery prices such boats are usually operated commercially. And I totally agree, there is a bright future for electric boats in the commercial sector. On popular beach destinations, all the snorkeling tours will be operated with an electric boat pretty soon.

    I did my part of research... boats, batteries, electric motors...

    First, I couldn't agree more with fallguy saying "I'd plan the boat build for electric."
    Transforming an existing boat into electric makes sense in about less than 1% of cases. Center of gravity, bouyancy, stability...etc
    You need a hull with minimal drag, with a very good prismatic coefficient.

    Have a look at this guy's project:
    Blue Planet 32E - Blue Planet Catamarans - Setting the Environmental Standard - Powered by Torqeedo electric outboard motors http://www.blueplanetcatamarans.com/32E.html

    Have a look at this, solar-electric catamaran:
    Solar electric catamaran | Soel Yachts http://soelyachts.com/soelcat12-solar-electric-catamaran/

    Since I would use a catamaran like this for commercial purposes, I did my research focusing on durability and safety. (higher price range equipments)

    As for the solar panel: currently Sunpower (USA) has the best flexible cells on the market with around 22% efficiency.
    Even if you cover 40m2 of the roof with a 8-9 kWp system, the max daily kWh generated will be around 6 (depends on location, insolation, etc). A solar roof on a commercially operated catamaran is a nice feature, good for advertisement and PR, but not really practical, and costs around 30-40k USD. I would rather glue realistic looking toy solar-panels on the roof for PR... much cheaper.

    For a commercial operation (let's say snorkeling tours, 2-3 hours per tour, 3-4 tours per day) you will want to determine the speed and range you want.
    I'd say a cruise speed of 7-9 knots is good enough. The distance you want to cover per tour you can calculate easily, but always add an extra 20% (wind, currents, etc)
    Now based on the total daily planned distance you can calculate the electrical motor and battery pack size.
    I was calculating with 20-22km / tour and 3-4 tours per day. Two 30kW motors could do the trick.

    Regarding the batteries: this is the most important part of your system. You are planning a commercial operation, you want a reliable system.
    Using cheaper batteries might be tempting, especially if you see conversions like this:
    Converting A Speedboat To 100% Electricity https://evobsession.com/converting-speedboat-electric/

    What you don't want is overheating. That is dangerous and not so good for battery life. Using cylindrical cells won't make sense. There is also a huge difference between the price&weight&efficiency of these batteries, I have compared the 18650 (tesla) cells to the Torqeedo (BMW) cells, different weight, price, cooling system.

    The best there is on the market currently is Kokam. Have a look at their cells:
    Lithium Ion Polymer Cells - High Energy High PowerㅣKokam Battery Cells http://kokam.com/cell/

    to be continued...
     
  6. gzs
    Joined: May 2018
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    gzs Junior Member

    These batteries are very efficient (96% @ 0,5C, 94% @ 1C). You can decide which cell to use. For two 30kW motors I would use 2x60 kWh battery packs.
    Why? Because I need the extra power. I'm planning a commercial operation. If there is any kind of emergency, and I have to return to shore, there has to be a healthy reserve to reach the shore at a greater speed than 7-8 knots. Also, 60 kW motors, 120 kWh battery pack means 0,5 C discharge rate.. no overheating, no battery cooling system needed. Also, keep in mind that you won't want to discharge your batteries under 25-30% SOC. That is again bad for life span.

    The price is high, yes, I know, these cells cost 1-1,5 USD/Wh. But I'm planning a commercial operation. These batteries last more than 9 years (and they will be around 90% of original capacity). Refueling would cost around 20 USD per day. Maintenance is around 3% of the boat's value per year (that's around 10% for ICE engines). The boat's capacity would be around 15 persons. If you do the math for 10 years, you'll see that such an investment makes totally sense.

    With such a boat, you could operate anywhere, even in protected marine zones. No emission, almost silent. On high-end tropical islands with many wealthy tourists you can easily get 60 passengers per day, for an eco-friendly zero emission snorkeling tour. There are a lot of people who would prefer this option even at a higher price.

    I'm not an engineer, nor a mechanic. I'm doing continuous research because I think there is a huge potential in electric. Anything that is zero emission and eco-friendly would be welcomed anywhere. You cannot find that many professional commercial operations based on electric marine vehicles.

    So I would be very much interested in such a project. I believe that 2x30kW motors and a 120 kWh battery pack would be ideal. The price of the whole electric system with BMS, charger etc would be around 200k USD.

    To be continued..
     
  7. gzs
    Joined: May 2018
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    gzs Junior Member

    What I don't know however, how much a catamaran hull would cost, or how much it would cost to desing a new hull.
    There are a lot of naval architects here, maybe somebody already has done something similar.
    Let's say 14m LOA, width 5-6 meters, comfy for 15 passengers + 2 crew.
    If anybody has a CAD file of a similar catamaran hull, using Maxsurf or any other marine software it would be possible to add the electric system components and see what happens to center of gravity, etc..
    I would be very much interested to find out how much such a hull would cost.
    I did my calculations and ROI is 1 year in case of a high-end location. I would be ready to seriously consider investing in such a business. It depends on the hull price.
    Lots of builders and architects here.. so I hope someone could give an estimate. Maybe someone has already built a hull ideal for such a venture.
    Let's just wait for the reactions :)
     
  8. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    I would write a summary to the ”boat design” section with a link to these messages.

    I believe the electric plarforms (and sub forums) are ignored as the typical case is utterly unrealistic. It was really refreshing to read your candid estimates.

    It is more typical to read about using crashed tesla batteries, ebay controllers, or rc-plane motors...
     
  9. gzs
    Joined: May 2018
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    gzs Junior Member

    Will do, since I'm looking for

    a) a 14m x 6/7m catamaran hull design for electric propulsion

    b) a max 6m LOA 2 person powerboat (tunnel hull or catamaran) hull design for electric propulsion
     
  10. xellz
    Joined: Jul 2017
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    Location: Japan

    xellz Senior Member

    Really nice to see someone with similar way of thinking. Only recently i got my hands on full plans for catamaran from Woods Design (due to incident, had to re-draw missing data) and with those plans i went on my quest to get necessary permits for commercial operation. But since it's rather unusual idea in Japan, paperwork going to take a while. I'm also short on funds now to go fully electric right from the star, no clear price tag on electric propulsion either. So i just bought used 28ft mono with diesel inboard for quite low price, about 12000$ for a boat in decent working condition with fishfinder/gps/radar and massive dolly for hauling out.

    Will be working on permits and start building when i can. Without any extra funding i have to do everything myself to be able to afford it. So as of now idea is, work with mono when weather allows, start building once permits are cleared and in meantime study electric systems so i can assemble and operate safely. Sadly this way it's going to take no less than 2-3 years to finish and i still think on hiring professional to at least design electric propulsion system.

    I spoke a bit with Richard before buying his design and it's really close to what i'm looking for. Custom design will cost a whole lot more. Efficient enough, quite light and relatively easy to build. Sailing Catamarans - Jazz 30 fishing, day charter or cruising http://www.sailingcatamarans.com/index.php/designs-2/6-powercats/438-jazz-30-fishing-power-catamaran
    As of now i'm think about 2x 15-20kW AC motors, inboard only, 60kW battery pack. LiFePO4 is a bit too heavy for my project and after some research i also ended up with Kokam Battery Cells. Since need high energy density, high cycle life and safety... will cost quite a bit more than i hoped at the beginning.
    No large solar array is planned for same reasons, it's not really practical for the price. But it is tempting. Majority of time speed will be low, there is no need to go above hull speed for sightseeing tours and most fishing locations are also relatively close. And will be slow trolling at 4-5knots anyway. Extra power for sudden weather changes or go against tide currents occasionally. With this kind of use solar array is not useless, good investment? Probably not.


    I'm considering moving to more tourist friendly location, like few popular islands in Okinawa. Japanese are fairly wealthy and multihulls are rare, electric is almost non-existent. Catching attention won't be a difficult task. Although current location has some good points. Unique scenery with active volcano, hotpsring by the sea and no competition nearby. Every year at least 2-3 tv shows come, for example in 3 days 1.5h special will be aired. 「滝沢秀明の火山探検紀行~巨大カルデラの謎に迫る」2018年5月30日 夜9時~ │ NHK http://www.nhk.or.jp/darwin/special/volcano.html I actually climbed volcano with NHK crew, so might appear somewhere :) Was great chance to climb, since can't go without permission, guide and special equipment.
     
  11. gzs
    Joined: May 2018
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    gzs Junior Member

    Well, what would be your operational profile? What is the planned daily cruising distance and what is the required cruising speed? What are the typical sea conditions in the area?

    Regarding the permits for commercial operation... Most certainly there will be a post construction assessment. I would make sure that I'm using equipment which is certified (example: Echandia Marine - Leaders in electric ferry propulsion systems and marine consultancy | Products http://www.echandiamarine.com/products.html , their equipment is DNV certified, the Kokam batteries are aswell).

    A good place to start getting familiar with the rules and standards might be:
    https://rules.dnvgl.com/ServiceDocu...DNV GL rules for classification: General (RU)
    Just download the whole package "download for offline use", over 300MB, but then you have everything you need. Start reading the file "DNVGL-RU-SHIP-Pt1.pdf". As a matter of fact, read it from the beginning to the end. It will clear a lot of things.
    Regarding the electric propulsion & battery system.. have a look at file "DNVGL-RU-SHIP-Pt6.pdf" see pages 194-213. That should give you a pretty good idea about the required standards.

    If you can elaborate the planned operational profile, I might be able to tell what I'd do... like I said, required range, cruising speed, sea conditions, max capacity, etc..
     
  12. xellz
    Joined: Jul 2017
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    Location: Japan

    xellz Senior Member

    Sightseeing tour mostly around the island, circum navigation around the island is roughly 18km, 2-3h with some stops. Drop off lightweight kayaks or sup board to enter hot spring which is accessible only from sea, only 3km from dock. At most 12ppl including me and helper.
    Recreational fishing around the island, full day. There is no need for long trips at high speeds, island is located on the edge of gigantic ancient caldera and that's exactly where most sweet spots are. I.e. short sprints of 5-15min at 12-13knots, depends on conditions spend 30min-2-3h at location, no anchor, re-position at slow speeds. Reasonable limit would be 5ppl.
    Commercial fishing, mainly single line fishing from various locations, trolling at 4-5 knots. No anchor, slow maneuvering almost at all times. Alone.

    Thanks for the link, have to add a whole bunch more for Japan. At least it's a lot easier for boats under 12m LOA and 12 passengers or less.

    Catamaran i'm planning to build is most efficient up to 6-7knots or 12+ knots. My rough estimation based on Richard's Skoota28 and his fuel consumption/rpm data would be 3-5kw/h at 6-7knots, 18-22kw/h 12-13knots depends on load. Jazz30 is 2ft longer, lighter and with less windage, in addition i saw few examples with not so efficient solutions consume even less power. But i rather plan on most highest estimation than be sorry latter.

    Sea conditions a bit difficult for me to explain, don't have videos. Random video from youtube, something like this is more or less the usual sea condition During summer can enjoy some days of almost completely flat seas.
     
  13. gzs
    Joined: May 2018
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    gzs Junior Member

    If you plan 1 trip/day, 18km.. I woul calculate with 22-25km, just to be safe..
    You're right about consumption, it's only a rough estimate but 5kWh for 7 knots sounds about right.
    I wouldn't do any kind of short sprints @ 12-13 knots, to be honest. It would eat up the battery so fast... which is not good for the life span. Well, maybe at the end of the trip, I would cruise at a bit higher speed.
    If you want your batteries to last long, you don't want the discharge rate (C) to be high. That means, for example, for a 30 kW motor you'll want 60kWh battery pack. Kokam can easily help you determining which cell to use, I can give you a rough example for a 150 Wh/kg cell: at 1C discharge rate 2000 cycles until you reach 80% DOD. That's 2000 operational days. At C/2 discharge 3000 cycles. C/6 discharge: 4500 cycles. C/12 discharge: 6000 cycles. You have to do your best to determine the speed (discharge rate) during your trip, but in my opinion, even if you charge/discharge with 1C, 2000 cycles mean over 5 years. But if you go at max speed, that means 2C discharge rate or more... the batteries won't last 2000 cycles.

    So if you want to cover 25 km, that's roughly 2 hours cruising @ 7 knots speed. Let's say your consumption will be 5kWh @ 7 knots. You'll need 10kWh for 2 hours, but we don't want the SOC go below 30% so that means you need 15kWh. Another question is the battery efficiency at your C rate and ambient operating temperature. Kokam's are really good in terms of efficiency, but let's say they'll be 90% efficient. That means you'll need a 17kWh battery pack.

    If you're running a commercial operation, always prepare for the worst case scenario (volcanic eruption, etc), and focus on safety. You want a healthy power reserve for emergencies. Instead of mounting more batteries, which is expensive, the best solution would be to have a reserve petrol outboard on board. The authorities will probably tell you the same, for emergency purposes.

    If I would want to do the conversion quickly, I would probably consider Torqeedo. Approx. 2x22.400USD (net) for the 2 outboards (Electric powered outboards for boats - Torqeedo https://www.torqeedo.com/en/products/outboards/deep-blue/deep-blue-40-t/M-3207-00.html), continuous 27,6kW. Handle the range details on their site with reservation. As for their batteries... they are cooperating with BMW, using their cells.. I don't have any information about the cell's cycle life at various C rates, their energy density is 1,5x lower than Kokam, I suspect that is because of the built-in battery cooling system, that explains their high weight aswell. They have a very efficient cooling system, no wonder that they give you a warranty for 4,5 years even when using their battery for commercial operations. I wouldn't go for the 30kWh battery as it is 1 piece and heavy... I'd go for 6 of the 48-5000 batteries, for easy weight distribution (5200 USD net x 6). Add a couple of thousands for throttle, BMS, wires, propellers... and 10k for the reserve outboard. That's around 100k USD net. A good thing to do would be to determine if this setup would pass a survey. Those Torqeedo batteries are waterproof, the whole system is very professional, and obviously we can't stress enough the importance of safety regarding salt water+high voltage electric system+lithium batteries. The extra weight of the 2 outboards+battery packs + BMS would be around 500-550 kgs. You should focus on distributing the weight in a way that your center of gravity remains more or less the same. Draft will increase. Passenger capacity will probably be lower. There are so many determinants, that I would just hire a marine surveyor, mount weights according to the proposed electric installations (2x145kg dummy weight for the outboards, 6x37kg dummy weight accross the hull, etc) and see what happens to bouyancy, center of gravity, draft, etc.. I would let the surveyor do a survey according to japanese standards... and if the boat succeeds with those weights, you could start ordering the electric parts.
     
  14. xellz
    Joined: Jul 2017
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    Location: Japan

    xellz Senior Member

    I don't want outboards, especially torqeedo. Use high end liquid cooled AC motors, more freedom with battery location, at 15-20kw per motor can easily avoid saltwater cooling. Total price should be noticeably lower than PMDC motor solution, safety should be better too. Absence of noise is biggest part of why i'm going through all the trouble, electric outboards while not really loud, can be annoying to some even more than conventional ICE outboard. Inboard solution is more quiet to begin with and in addition can add extra noise isolation without too much trouble. Space that could be taken by outboards can be used for kayak/sup board launching or nice fishing spot, easier to fight large fish too.

    I'm not going over 1C, to reach 12-13knots need roughly 20kW. General use will be way below 0.5C. From what i found, Kokam cells can be discharged up to 10-15% without any ill effects. I.e. there won't be noticeable difference in lifespan if i use 50kw in one go and charge once or use 25kw, charge, use 25kw more and charge again. But either way, there should be back-up power, need small generator that can keep the boat at least at 4-5knots. Small 9.9hp outboard can also work for this. So what i ended up is, i need current NMC tech to make this project practical. At around 140-150wh/kg it looks fairly good, at least on paper. Suitable LiFePO4 batteries that i could find are at best 90-95wh/kg, too much of a compromise to continue with this expensive idea. No doubt will be fun, but i can't spend so much to just have fun myself.
     

  15. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Electric is still a rabbit hole unless you are going from dock A to dock B half mile; despite all the efforts; costs are just too high. And battery life will get more $$.

    Put a couple of Yamaha 70s on the boat. They cost under 10k each. You can get the boat up above 20kts and sip fuel at 8-10kt cruise.
     
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