Solar catamaran

Discussion in 'Multihulls' started by guzzis3, May 20, 2021.

  1. SolGato
    Joined: May 2019
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    SolGato Junior Member

    Here is an example of a basic electric powered Catamaran in the size range Guzzi originally proposed.

    This is a good example of what you would get if you took a modern lightweight hull and added a pair of electric outboards to it.

    Even without a big hardtop covered in solar, I think a setup like this is only good for Bays, Coastal cruising, etc..

    Get a boat this big with a top on it out in some swell and wind, and you aren’t likely to make much headway without running out of juice.

    One option would be to have a big centrally mounted ICE motor that you use in the rough stuff, then when you are close to shore or in calmer waters you can cruise around comfortable and quietly on electric propulsion.

     
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  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The cat may not be the ideal candidate for the slow-poke solar boat, it has more wetted area per unit of displacement, and at crawl speeds it is skin friction that constitutes the main retarding factor, neglecting wind.
     
  3. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    I can't see as well as I used to but I think that boat was using the 2kW input 1150w output torquedo C2.0. The motors I linked to are 2200w input 1430 output so potentially a bit better performance, but a very helpful link. I couldn't see the speed they got and of course you don't know how fat the hulls are or how heavy it is. But imagine that boat with a flat thin roof over. Shade, you could even fit gutters and collect rainwater for washing etc.

    I don't understand the concerns about windage. A 32' sailing cat would typically carry maybe 42sqm of sail presented directly to the wind. Why would a thin horizontal roof structure present a windage issue ? Likewise consider the weight aloft of a rig.

    Some of the comments seen to indicate I was proposing this alongside a sailing rig. I was actually suggesting a pure electric motor boat. Obviously it would not motor 24 hours a day. Also like any boat that size you'd need to pick your weather. By my calculations it should be able to cruise at hull speed, around 6 1/2 knots, up to 10 hours a day. As a coastal cruiser that is pretty tolerable. Remember there would be no beating. Conditions permitting you just plot the shortest distance between 2 points and go. Chop and currents would slow you down but they do anyway.

    And when your at anchor that roof will recharge batteries then run a watermaker. And the rig would cost similar money to a sail rig, auxiliary and batteries.
     
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  4. guzzis3
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    guzzis3 Senior Member

    That was my concern with the extremely long and presumably thin hull boats mentioned previously. There is a sweet spot for length/beam when you have relatively little power to play with. Very long thin hulls at these low speeds would suffer from skin friction. You could of course increase beam for more roof area, say push it out to 20'. A backup generator would be a good idea. A coastal cruiser has options. I think crossing oceans is a whole other level of difficult.

    Also those motors aren't especially efficient. You might get a better output vs energy consumption with a carefully chosen inboard motor.

    Anyway, interesting stuff.
     
  5. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Can solar panels be made light enough to be the fabric in the sail?
    Is a fixed shape sail, ie lightweight composite with attached somewhat flexible solar panels feasible?
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I would look at it as an adjunct that can be used when conditions suit, and the requirements of the day fit, you could troll all day for free, for example.
     
  7. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    https://www.solarclothsystem.com/home
     
  8. SolGato
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    SolGato Junior Member

    You can’t just go by the calculations. There’s a big difference between the Torqeedos (yes they are Cruise 2.0) and the motors you linked to.

    For starters, the Torqeedos use planetary gearing whereas the others are direct Brushless.

    So some of their inefficiency is due to the gearing, but the planetary gearing allows Torqeedo to spin a much bigger more aggressively pitched prop. This is why they would be better suited for a larger boat.

    The other motors are basically just big trolling motors designed to move a heavy boat around slowly, or a small one around efficiently.

    I have seen a pair of those 160lbs 48V motors on a large cat, a Gemini I believe, and the owner had cavitation and prop slipping issues which resulted in poor top speed performance.
     
  9. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Oh sorry, I just noticed I attached the wrong PDF for the solar range previously.
    I've added Brisbane to it and set it to 34m² solar (this would be for 8.5m x 4m solar roof). Looks like Australia is a very good location for solar cruising!

    The spreadsheet takes the average solar power on a horizontal surface in kW/m²/d which includes diffuse scattered light from clouds. Then multiplies it with the efficiency of the solar panel (20%) and the size of the roof area for the daily gain. Then just calculates how long you could motor with that daily power and the resulting range. This doesn't take battery reserves into account.

    The summer is the average of the 4 summer months, spring/fall the average of each of the two spring / fall months, and winter similarly.

    So with 3kW power use from the motors at 6 knots you'd generate enough solar power over a day to cruise for about 10 h. The question is how realistic 3kW @ 6 knots is. I imagine a single center pod and larger prop could be more efficient?

    Australia Winter 8.7 h 51 M
    Australia Spring / Fall 13.5 h 79 M
    Australia Summer 17.0 h 99 M

    SolarPowerAndRangeCalculations.png

    Ideally on a boat you'd have a range calculator app that takes the current date and position and expected solar gain for the day and the battery status and calculate the expected range. Adding a route planning with expected wind and waves would be more involved.
     

    Attached Files:

  10. Dolfiman
    Joined: Aug 2017
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    Dolfiman Senior Member

  11. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Interesting point about the orientation of panels, but it adds complexity.
     
  12. SolGato
    Joined: May 2019
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    SolGato Junior Member

    If you’re going to go the route of using ridged panels, certainly it would be wise to invest in Bi-Facial panels. A Bi-Facial panel can offer as much as a 30% in power.

    For example, a 375W Bi-Facial panel can provide almost 490W of power in the same size footprint as a one sided panel.

    As stated, water is reflective and space is limited, so you might as well maximize your power capability.

    Granted you don’t get a 30% at all times, but when you do get that added power performance it can make a huge difference in bank recovery or offsetting loads like electric motors.
     
  13. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Using the sides of the hull could help but the practical efficiency per area will be quite low. So it would make sense with flexible panels. But flexible panels are like 2-4 times the cost, last only half as long and are less efficient with 15-18%.

    Overhangs that can be angled up or down could also capture light in the evening or in the winter months or when you travel east / west.

    There are also those bifacial solar panels that look quite beautiful on the energy observer as awnings. They can gather light from both sides so theoretically awesome catching the reflection off the white deck. But only up to 23% efficiency best case while the maxeon panels can reach 24% without bifacial.
    EDIT: Apparently up to 27.6% now!
     
  14. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    SolGato: Thank you for that. I understand the trolling motors have issues. For one thing they come with the wrong prop and apparently finding the right one isn't straighforward. A person on a TS forum did the experiment. Hegot it to work ok as an auxiliary but it wasn't ideal.

    But you can get efficient electric motors that could easily be rigged as inboards if the boat was electric only.

    Dejay: I haven't been able to study your calculations. One thing they might be missing. Qld gets nearly all it's rain in the wet season, september to march. It is not uncommon for us to gt pretty much no rain for 6 months. Likewise cloud cover is sparse in winter. Winter is when you go sailing. Summer we have killer jellyfish, cyclones, suffocating humidity. Our winters are probably like European summers :D 10C overnight and low 20's during the day.
     

  15. Oliver Lichtenstein
    Joined: May 2021
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    Location: Hamburg, Germany

    Oliver Lichtenstein New Member

    Happy to join the party - I'm currently working on a similar project. 11m x 4.5m catamaran that served as a tender / lifeboat on the Holland American (cruise) line.

    It's not exactly an efficient hull design, but better than a standard monohull nonetheless. We're currently running calculations / CFD to find out exact power requirements.

    The Tûranor was actually built next door (100km from Hamburg), so I'm trying to get in contact with some of the people from that project and am planning to do a sliding wing concept similar to theirs.
     

    Attached Files:

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