Choosing the best marine hull for an autonomous boat

Discussion in 'Boat Design' started by Anelito, Aug 6, 2018.

  1. Anelito
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    Anelito Junior Member

    67W considering motor always on
    10 average full sun hours
     
  2. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    If 10 full-sun hours then you could get 11 - 12 full charging hours from your MPPT at 100W
    That would support a 45-50W average draw, 24/7, not 67 though.
    So, you'll draw your battery down until the LVC (Low Voltage Cutoff) disconnects everything.
    Reconnect will not occur until sufficient battery voltage is achieved.

    You may want to run your electronics on a separate battery, diode protected, even though you'll
    have a motor controller throttling back at diminishing battery voltages in order to avoid the above situation.
     
  3. portacruise
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    portacruise Senior Member

    You might need to add enough battery storage (or a lighter back up system) to allow for a run of consecutive days without sunlight during Rain, storms, clouds, Etc.

    PC
     
  4. BlueBell
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    BlueBell Ahhhhh...

    Like I said before, I don't think the OP is very sincere about this project.
     
  5. Anelito
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    Anelito Junior Member

    I made rough estimations about solar panels, that is true, because until I have a prototype to test with I stick to the (fairly inaccurate) power graphs of solar cells producers.
    If you see any chance of exploiting the project in other areas than pure research you are welcome to, as long as you comply to the GPL licence on the GitHub repository of the project.

    Some interesting data I found on a forum, following one of the SeaCharger guys reply:
    SeaCharger did about 3 knots in calm water on about 20 watts and weighed 60 lb. The average speed from California to Hawaii was 2.1 knots.

    Now I was wondering how can a 20W motor drive such a heavy boat when RC boats use up to 1kW motors and are less than a metre in length.
     
    Last edited: Aug 22, 2018
  6. Anelito
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    Anelito Junior Member

    So I've come to the conclusion I will need either to consider running the motor only half of the day or to include an extra power-harvesting system as it is extremely difficult to find good brushless motors with enough torque to run a big propeller under 100W. I am now considering adding a micro turbine. Wings can be set to different angles of attack so it should be able to withstand strong winds.

    [​IMG]

    For the hull, I have been suggested to look at those (paid) vintage class M designs:
    Water Baby 'A' - Plan - Sarik Hobbies - for the Model Builder https://www.sarikhobbies.com/product/water-baby-a-plan/
    Duckling RC1344 - Sarik Hobbies - for the Model Builder https://www.sarikhobbies.com/product/duckling-rc1344/
     
  7. JamesG123
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    JamesG123 Senior Member

    I LOLed.

    Sorry. Its like you are in a hurry to do nothing or something.

    What about when they get knocked down into a wave while they are spinning around in that strong wind?
     
  8. portacruise
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    portacruise Senior Member

  9. Anelito
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    Anelito Junior Member

    Well I'd like to start testing in October, during winter it will be difficult due to bad weather.

    That's an interesting question. The boat can sense wave movements using an accelerometer, so I could set the turbine blades to go in neutral mode and stay still. During a storm almost all the systems go in stand by to avoid wasting energy and causing damage.
     
  10. JamesG123
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    JamesG123 Senior Member

    That's not likely if you keep creeping the scope out of your project...


    Yeah... um no. You really don't know what the open sea is like do ya?
     
  11. Anelito
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    Anelito Junior Member

    What's your suggestion in that case?

    I've been in the open sea in several occasions and experienced winds up to 7 on the Beaufort scale, that's nothing compared to a real storm but up to now solar panels calculations clearly show there are high chances of prolonged power loss, a cloudy day can be fatal.
     
  12. JamesG123
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    JamesG123 Senior Member

    You should be designing your system to deal with reduced charging and power loss anyway.

    You are designing some thing closer to a free floating buoy than a boat. You can have steerage and be able to make way, but to think that a solar powered craft can make steady hull speed is not very realistic. PV conversion (or any other generation means) and battery technology just isn't efficient enough, no matter what scale. Even sailboats with electric drive and large multi-generation systems (PV, screw regeneration, windmills, etc.) are more constrained than conventional diesel power. But they can stay out longer and of course do not need to refuel.

    Likewise, the primary advantage of an unmanned (anything) is its endurance, esp. if its solar powered. You have not said you are trying to break a record or race, only something about testing an "anti-collision system". Its not in any hurry, since you've (hopefully) engineer it to have the ability to remain at sea nearly indefinitely, it can ideally move with currents and winds or slowly beat against them to methodically go about whatever task its little robot brain has been set to. So you have to consider that, your limited power budget, and what objective you are trying to achieve.

    So focus on simplicity and robustness. A VAWT is neither of those things.
     
  13. BlueBell
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    BlueBell Ahhhhh...

    VWAT - Vertical Axis Wind Turbine
    13kg for 400 Watts, maximum, when it's blowing.
    On a tower, obstructing your solar panels.
    Really...? <wince>
    Even flush mounted ( no tower ), more than 60cm protruding.
    And what are the wind statistics for your area of operation?
    Like the "Sun Hour" statistics ( not guesses ), you don't know.
    Your vehicle is too small to support such a rig.

    400 W in flex PV is ~1/2 the weight.

    Perhaps you want to consider eliminating the propulsion battery
    and design your motor around PV only.
    This would allow for more panels while reducing over-all weight.
    Weight is the enemy of velocity.
    If you want collision avoidance at night, a small reserve battery
    could be programmed to kick-in when under threat of being hit.

    Although, battery keel-bulb weight is a nice optimization of evil.
    Combined with bang-for-your-buck on lifepo4's.
    A pro/con analysis would be prudent.
    Ah, the design spiral...
     
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  14. portacruise
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    portacruise Senior Member

    Solar Surfer made good progress, but we don't hear about all of the failures, it may have been a lucky lucky shot, out of a thousand others have tried! I believe the SS had periods where forward progress was reversed or stopped, and was thought to be dead, maybe the batteries went dead. The top speed will probably be during storms, as the autonomous may become airborne over hundreds of yards. The design should include considerations for maximum g -shock. Wind power probably has more usable energy than anything solar, but how to design a robot sailor control that pulls down sails as needed, makes adjustments to stay on course, etc?

    PC
     

  15. Anelito
    Joined: Aug 2018
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    Anelito Junior Member

    Bluebell
    I have a colleague who makes VAWTs with adjustable pitch and can lend me one of their prototypes, 50W at max, three-bladed and 60cm, doesn't need to be placed on a tower.
    I can't fit more than 90W worth of solar cells, I have to consider some space for lamination.
    Wind statistics aren't readily available like Sun radiation index, as they depend on the current weather. But if I make the blades lightweight enough, marine breeze can trigger the turbine too.

    For the batteries, I can fit 14 16850 Li-ion batteries in a tube of 6cm diameter, could be the bulb or the keel itself. Putting 7 in series and 7 in parallel I can get 15Ah and 26V for 600g. A metal enclosure will help with heat dissipation.

    portacruise
    I have contacted the OpenTransat team asking about their solution and the small free-rotating wingsail seems a good solution to back up the motor when the power harvested from solar panels is not enough.
    [​IMG]
     
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