Choice of electric motors as inboards for a catamaran

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

  1. xellz
    Joined: Jul 2017
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    xellz Senior Member

    Idea started with misleading 1kw electric = 3hp diesel. But with advice here i actually could put together more or less realistic project. Turned out a lot more complicated, but also quite a bit more interesting too, fun to learn about hulls, materials, propulsion etc.. My entire life was a headache for anyone involved with me, since i almost never go the usual convenient way :D Batteries were first, have several options with bms and various pack sizes available. If will try to ask if something like Tesla or Leaf packs can be used, but from recent info seems it's way too much trouble and most likely not worth it. Once i learn enough about inboard installation and requirements i'll go for consultation regarding propulsion system. I.e. battery, controller, charger, motor. This part i don't want to do myself, don't have the confidence that i can put together reliable and long lasting system.
     
  2. BertKu
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    BertKu Senior Member

    I fully agree with you. The problem with those statements, you might take OceanVolt for granted, because maybe they worked something out versus the worse scenario for a diesel versus the same speed of the brushless motor and that maybe true for that particular speed of propellers. But then one gets into a situation that one needs more power, which you don't have ( because you calculated the power on their marketing story) and you will be in deep trouble. I still haven't heard on my request to explain under what conditions they can make that statement. One thing is for sure for brushless motors, the power to your motor is quite linear. i.e. 1000 watt from the battery = particular speed 2000 watt from the battery will give double speed. The reason is that the torque is nearly linear from 1 rpm to 3120 rpm for a 130 KV motor ( 130 x 24 Volt = 3120 rpm) at 6 Volt it will be 130 x 6 = 780 rpm. At half speed 1560 rpm, you consume basically 50 % power. If you have a 8000 KV , (used in a aircraft) you will probably only work with a 6 Volt Lithium battery ( 48.000 revolutions for the propeller) Well we will be looking forward to your experience. Good luck. Bert
     
  3. iskip
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    iskip Junior Member

    Hi xellz and all others
    I'm in the same situation and I would like to build a full electric catamaran. I understand with"Full": 100% without petrol. I dont like to use a petrol genereater, I would like to use a recuperation system with my both electric motors. My cat is a 44ft bluewater crusing alumium catamaran with 9-10t, but it is not finish builded (i hope it is finisch in 2021).

    Here my datas (I think, this is a good solution):
    2x 10kW(maybe 15kW) Electric Engine inboard with shaft
    3 or 4 blade propeller, 17"
    recupration over the electric engines under sailing
    45kW battery bank (48V), Lithium
    1-2kW solar panel
    self-sufficient system

    Why I would like to use a recuperation?
    The most output of energy is, when i go sailing. In harbor, storm, windless time, rescue, .... The waterpower is so much stronger then the windpower. For charging is it necessary to have 2-5kW/h. A wind gerenator give only 0.5kW/h. Solarpanel give energy only at the day and only when it is sunny. To use more time or lose speed is not important, then I'm a blue water sailer.

    My big question/problem:
    - Which electric engine is good for to use as motor and as gerenator? Brushless? AC/DC?
    - recuperation: When i use a DC Engine, and go sailing, then i become different Volt. How can I transfer this in my batterybank with a good efficiency? With a AC/DC/AC transformer with different input settings (AC/DC)?
    - They are brushless engines more silent then normal electric engines? The engine is unter the floor of a sleeping room.
    - Is it bether/easyer to have 2 engines, a power-enging and a generator-engine on the same shaft?


    What do your think about my idees/wish/questions?
    Iskip


    (Sorry for my bad/simple english. My mother tongue is german)
     
  4. BertKu
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    BertKu Senior Member

    Gruss Gott Iskip,
    With that kind of power in mind, I would strongly suggest you consider to look at "www.Oceanvolt.com" and select the correct drive. The motor is at the same time the re-generation of energy to your battery. Please buy a more expensive solar panel which also charges the battery during the night. Also the open Voltage of a solar panel is important when you use a MPPT controller, as by low light and sun ray angle the battery gets still charged somewhat. The Chinese claimed to have plans to produce them. Do some Google searching. Bert
     
  5. iskip
    Joined: Jan 2014
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    iskip Junior Member

    Thanks Bert.
    Oceanvolt offer only up to 8.3kW, and the price is very high. only the Saildrive have 15kW, but i use a Shaft.
    I prefer standard elektro engine from business. 1 Engine cost 900 - 1'500€, and this price is far away from oceanvolt, mastervolt, torquejet, Kräutler, and others. Its is cheaper to buy 3 engines between 15 years than 1 from a boat company. The system is the same.
    On bluewater you have also to us standard parts. KISS princip (Keep it simple, stupid) is importend on board.

    It is impossible that solarpanel can charge battery in the Night. Sunpower is 1000W/m2 and full moon power only 0.003W/m2.
    I try to buy my solar panels in the last moment (maybe 2021) in the hope, they are better and cheaper. The problem with the shadow on a boat (lines, stacks, mast, bom, ...) is a bigger problem, than the effectivity. I hope for better solution in the next 5 years.
     
  6. iskip
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    iskip Junior Member

    Have you got pictures from that, or a webpage? That sound very clever!
     
  7. BertKu
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    BertKu Senior Member

    O.K. Iskip, that make sense. What do you mean with "standard elektro motor" Do you mean a 20 Kw brush less motor like they use for your German helicopters? Or a 230 Volt AC motor? If you use a AC motor you need to consider a forward and backwards system and you cannot generate electricity easy by sailing. If you use a brush less motor , you need a 75KV per volt. i.e. 75 turn of the motor coil winding gives you 1 Volt. If your battery bank is 48 Volt, your sailing system must gear it up so that you get at least 57 - 60 Volt to charge the batteries. Although your lithium batteries are charging already at 2 Volts per cell. This is much lower than a lead acid battery. I use 130 KV brush less motors and am struggling to make a decent current regeneration system. It also means that at 75 KV, your motor runs at 75 x 48 = 3600 rpm only, thus a large blade. Which when sailing maybe of a disadvantage. Secondly normally the propeller does not turns as fast as being driven by the batteries. I.e. you need to build or buy a voltage doubler or tripler. Your prop during sailing, may only turn 1200 - 2000 rpm and it produces only 16 Volt - 26 Volt. Or you must make a system whereby the brush less motor get geared up when sailing.
    With respect to solar panels generating electricity during the night, the cells are producing at a different wavelength the energy. But it is still very expensive and in the "baby" shoes. You could consider to buy solar sails from contact@solarclothsystem.com, then your problem with shadow maybe solved. I haven't contact them and does not know what they are costing.
    Bert




     
    Last edited: Aug 27, 2017
  8. BertKu
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    BertKu Senior Member

    Iskip, I posted a brush less motor in transformer oil in thread "props" refer
    Is there a systematic way to balance a prop It works extremely well for 6 years already. Bert
     
  9. gonzo
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    gonzo Senior Member

    Have you consider a variable pitch propeller to optimize charging?
     
  10. iskip
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    iskip Junior Member

    This would be the perfect solution, but where can I find one with 17"? I like the idee, because, when I dont use the charge or power, I can set the propeller neutral. Do you know a company?
     
  11. gonzo
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    gonzo Senior Member

  12. iskip
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    Location: Switzerland

    iskip Junior Member

  13. Rumars
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    Rumars Senior Member

    Regeneration is possible but to get to your stated amounts of 2-5kWh your boat either has a lot of sail or there is a storm. You are braking the boat while regenerating. And it will work only above a certain speed.

    The motor you select has to be able to regenerate. This usually means either permanent magnet synchronous motor (brushless AC) or a asynchronous motor (AC induction motor). Other motors are also capable to regenerate (separatly excited brushed DC or brushless DC are the easiest to use). The regeneration part like the driving part is done by the electronic motor controller. You don't have to worry about what voltage your motor produces, you just select a controller capable of regeneration appropiate for the selected motor. This is actually the expensive part of the setup, the motor is cheap.

    The hard part is you wanting to regenerate at high rates. To produce the needed power the propeller has to spin at a certain speed. Since a propellor is optimised for driving and not braking the only way to transform it into a repeller is a CPP (controlable pitch propeller). West Mekan and Sabb make what you want. To use the CPP efficiently you would have to have a dedicated control unit that varied the pitch acording to rpm in order to produce the most current. Even with such a control unit (that you would have to make and calibrate yourself, there is none for sale) the rpm's available at the shaft are limited by boat speed. To produce high power the generator either has to be compatible with that speed or you have to make it compatible by gearing it up. And your sails must be able to provide the power needed without the generator slowing the boat down significanly because if the speed drops the shaft rpm drop.

    If I would do it, I would forget generating with the main engines. I would install a complete separate generating unit between the hulls either on a pivoting shaft or on a folding outboard bracket, with a windmill generator head and charging unit and a repeller. Why do you want such high generation anyway? Are you planing on electric cooking?
     
  14. gonzo
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    gonzo Senior Member


  15. iskip
    Joined: Jan 2014
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    iskip Junior Member

    Thank all for all the precious information. :))

    My consideration is follow, why i would like a recuperation (I'm not a electrician, I'm a mechanical engineer):
    When i look the Cruising hydro generator http://www.wattandsea.com/en/cruising-hydrogenerator they build 600Watt with a propeller of 240mm and 9kt. Yes, i would like 2kW/h, and so i could buy 3 of them, and i hav it. But why i sould invest this money, when I have 2 electric engines? I my brain is it only a resetting of the contacts, and a elektric engine is a electric generator.

    Why 2kW/h?
    I beleve 2 times a hard storm, and they take us over houres. On a catamaran is it importand that we hav'nt a capsize, so we have alltime to look, where the waves come from and sail in the waves. So, the engine is alltime in work/use. A batterybank of 45kW is fast used. More than 45kW make no sense, because the weights is to heavy (a catamaran is very weight sensitive) and it is more expensive. with 2kW/h is the batterybank (from 40% to 100%) in 14h full (99% of live you never go lower than 40% and the livetime of cells is higher).

    My vision is it, to have a boat without pollution of oil, a boat for the future, sail around the world without pollution but with modern comfort. I think, it is possible today. The only other energy source that I can accept is gas (propan/butan).

    This discussion here bring me to other ideas and bring me step by step forwand. Very thanks for your help.

    Thanks, very interesting approach, but I have to go through the head first.


    Thanks, a lot of good facts. I like mathematics. It give me other view of electric. rpm over 2000 make no sense, because then I have a lot of vibration and sound on the hull. A good range is 1050-1500 rpm and that produces 14 - 20 Volt, simular to solar power or wind power. Now I unterstand also, why it is so difficult to have a 24 Volt DC system on board, because a genereator have to work with 2100 - 3000 rpm.
    Of course, a batterybank with 96 Volt or 134 Volt is better for the engine, but a electricion told me, it is saver to build a system under 50Volt DC, for that I would like to have a 48 Volt batterybank.
     
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