Help me design the "Poorqeedo", another efficient electric boat

Discussion in 'Boat Design' started by mental_boy, Jun 2, 2010.

  1. mental_boy
    Joined: Jun 2010
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    mental_boy Junior Member

    Rick, thanks again for all your time. It's really great to have your experience and skill as a resource.

    I'm thinking of abandoning the catamaran plan and going with the monohull. Not only will the hull have less hydrodynamic drag, I also believe the boat will weigh quite a bit less and have significantly lower windage. The only disadvantage is the weight of the hull when broken down for transport. I may end up needing some kind of aid for loading it on my vehicle.

    I attached some quick sketches of possible seating arrangements for the monohull. I like the wider arrangement for comfort, but I am leaning toward the narrow arrangement for lower weight and ease of paddling.

    Some questions remain. How would the outrigger(s) be constructed? Should I have one like a outrigger canoe? Or two? What would they look like? If I am motoring across the wind and one is always in the water, how will that affect performance?

    I bought another motor, shown in the attached picture. I got lucky and no one bid, so it was only $0.99 plus $16 shipping. It's new, 24V, 550w, 220 rpm. Not sure how suitable it is for this application, but at 36v with the same amperage the motor will do 825w at 330rpm (assuming it holds).
     

    Attached Files:

  2. Guest625101138

    Guest625101138 Previous Member

    Go for twin outriggers. They are set just on the waterline so you have a stabilised monohull. This is less draggy than a single outrigger, which will be twitchy - easy to roll unless it is heavy.

    The motor looks good. Do the measurements so we can determine efficiency. The scooter stuff is better sealed so you need to keep this one out of salt water.

    Suggest you get a copy of the free version of Delftship. It is not real hard to use and allows you to make more realistic images - I can send you a file of the starter hull that you can play with. It also allows you to produce images and cut files for developable shapes. I can then talk to you in more detail about the shape.

    With the 7m/400kg hull you should see 8kts (9mph) with 825W on the prop shaft.

    Rick
     
  3. Guest625101138

    Guest625101138 Previous Member

    I like the slightly wider of the two hulls. I think it will be a more sociable seating arrangement if you intend to carry four people. The batteries could be under the middle seat. You could make it a tabletop. It is best to have the batteries low and in the middle of the boat.

    The wider boat allows you ti shift the crew weight off centre to avoid a list in wind. Having an outrigger loaded will add drag. It will not be huge - a speed reduction of 5% to maintain the same range. Windage on the nose will be much more significant in terms of added drag. Could slow you down by more than 10% for the same power. So aerodynamics of deck and beams are important.

    Rick
     
  4. mental_boy
    Joined: Jun 2010
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    mental_boy Junior Member

    Thanks, I'll go with twin outriggers.

    I just purchased the motor this afternoon, so I'll take measurements as soon as it comes in the mail.

    Ok, will do. The images weren't meant to be realistic, I just drew them quickly to show the configurations. The proportions were just a guess, no measurements were made.

    8 kts is excellent. The only thing I'm concerned about is the low 330 rpm which means a high prop pitch. If my calculation is correct, the pitch would need to be 29 inches or 75 cm. Obviously it would need to be hand made, but is this an appropriate pitch?

    You're right, the wider configuration is better since it would be more sociable and it allows for balance adjustment. It wouldn't add much weight and paddling would be ok with a crew of 2 or more.

    The table is also a great idea.

    Again, I'm curious to know what you think would be appropriate dimensions for the outrigger pontoons, especially the length. The length dictates the location of the crossbeams and affects the seating arrangement. I'm also curious to know what you would think is a good beam for the boat overall.
     
  5. Guest625101138

    Guest625101138 Previous Member

    You can use a single outrigger beam but for your case I would go with two Aluminium tubes. You can slide these into tubes fixed in the hull. The sterns of the outriggers should not be very far forward of the stern of the main hull. You can get a bit of lift from the bow wave of the main hull if you set the width so the stern of the outriggers ride the divergent wave produced from the bow of the main hull.

    You do not need a huge amount of buoyancy to keep upright but the smaller you make the outriggers the more sensitive it becomes to weight movement.

    One of the potential issues is how you board from a dock. If you are coming alongside then you need to cross the outrigger to board. In this case the outrigger needs to be able to support at least one person. This may be a reason to make a more solid single crossbeam so it can be used as a gangplank.

    For outriggers my thoughts would be 3m long, 150mm wide and about 300mm high. This should give say 80kg if fully submerged. If you or crew are heavy then you might need a bit bigger. To stand on the deck of the outrigger they need to be 4-ply. If glassed inside and out you could go to 3-ply. The sides 3-ply is OK. Also 3-ply on the bottoms. Use blue or pink polystyrene foam or polyurethane foam for bulkheads. Polystyrene is stiffer but you cannot use with cheaper polyester resin. I prefer epoxy resin and polystyrene.

    The only problem with the large pitch prop is that this limits the minimum diameter. You do not want to go more than 2 for the P/D. Hence you need about 15" pitch. Most of my props have P/D of about 2.

    Rick
     
  6. mental_boy
    Joined: Jun 2010
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    mental_boy Junior Member

    I'll have to think about how I'll board the boat. I was originally thinking from the bow since I like the simplicity of aluminum tube. From the side could be more convenient in many situations. If I board from the side the pontoons will need to be significantly more buoyant since I weigh 105kg (This is how I am able to easily put out 750W).

    what kind of reduction in performance would there be if the pontoons were placed amidships, rather than toward the stern? I'm not opposed to putting them toward the stern, but I believe the boat would be less likely to capsize in rough weather if they are placed midway. I also prefer the appearance. Is positioning of the outriggers something that can be resolved with the model in delftship? i.e. can the divergent wave be modeled in software?

    Can you post the 3d hull model so I can begin making modifications in delftship?

    15" is fine, especially since the prop will fold. I need to think about where the motor will go with the new configuration since the footwells now interfere.
     
  7. mental_boy
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    mental_boy Junior Member

    Neat mill, Jeremy. I'm still very impressed that you're running it with a turnigy motor.

     
  8. mental_boy
    Joined: Jun 2010
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    mental_boy Junior Member

    Found this in another forum, seems worth reposting:

    "A single outriggers on a canoe is quite different to twin outriggers on a trimaran. With the later they should be set just on the water so there is no appreciable contact in calm water. Ideally they could be height adjustable to be set for the conditions.

    With sailing the outriggers can be set to carry the entire displacement when heeled and they should be as long as the main hull and slender for fastest performance.

    For a stabilised monohull you want iutriggers that generate a lot of lift with little immersion but will also easily punch through waves.

    Rick W."
     
  9. Guest625101138

    Guest625101138 Previous Member

    Extend the stabilisers out to about 4m so they will cater for your weight.

    If you mount the stabilisers too far forward the boat will flop-roll when you are running with the waves. The centre of the main hull gets suspended over the trough. This can mean the outriggers are both out of water and the boat rolls down onto one. Setting the stabilisers aft avoids this.

    You can also cater for light and heavy load cases by using boat trim. When light you trim stern down so the aft end of the stabilisers are just touching. At full load you have level trim with the stabilisers just above the water surface for their entire length.

    I have attached the .fbm file for the pq7 starter shape and a .part file for the stabilisers I use. Just scale this to suit. You can scale in Delftship different amounts on each axis. So say 240% for the length (x), 150% for the beam (y) and 220% for the height (z). Then check displacement.

    If you have a problem with Delftship just ask. It takes a while to get familiar. The main thing to remember is that it is a surface modeller. You can drag control points around and you can extend open edges. If you cut internal edges or control points you create a hole. The mouse keys have useful functions for zooming and moving. You can have four simultaneous view windows or open up to one full screen for detail.


    Rick
     

    Attached Files:

  10. mental_boy
    Joined: Jun 2010
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    mental_boy Junior Member

    Thanks.

    I'm playing with Delftship now, I'll be sure to let you know if I have any problems.

    The outriggers look nice.


     
  11. mental_boy
    Joined: Jun 2010
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    mental_boy Junior Member

    Ok, feeling pretty feeble at the moment. How do I check the displacement of the outriggers?

    So far about all I can do is move whole objects, stretch things and move individual control points. I should probably try one of their tutorials. Is there a need to actually model the deck in delftship?

    Stretching the outrigger 220% vertically seemed like a bit much, so I stretched it less....
     

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  12. mental_boy
    Joined: Jun 2010
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    Location: Oakland, CA

    mental_boy Junior Member

  13. mental_boy
    Joined: Jun 2010
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    Location: Oakland, CA

    mental_boy Junior Member

    Some random battery info.

    I've found that the deep cycle 115ah Group 27 Walmart batteries are made by Johnson Controls and are the exact same battery sold by many different retailers in the US:

    Costco/Kirkland ($69)
    Walmart ($70)
    Interstate ($75, wholesale)
    Sears Die Hard Gold ($99)
    Kragen auto parts ($99)
    Autozone Duralast ($?)

    The only different lead acid batteries I've found locally:

    Optima 55ah bluetop ( $150, also made by johnson controls)
    Sears Die Hard Platinum 85ah AGM (~$200, made by enersys)
     
  14. Guest625101138

    Guest625101138 Previous Member

    The value of doing it in Delftship is that you can get all the hydrostatic information.

    You can also produce developable pieces so it gives you the cutting files.

    Look at the layer properties to turn the hydrostatic data off and on. If you set the draft so the stabilisers are fully immersed and turn off the hydrostatic switch for the main hull you can see what the stabilisers displace fully immersered. If you need to board from the side then they need to displace your weight. If they do not then you will roll it when you board.

    It takes a bit of time to learn how to use it proficiently. But it is rewarding once you get a handle on it.

    Rick
     

  15. Guest625101138

    Guest625101138 Previous Member

    I extended the sides and fiddled with them to create something like the cockpit you drew by hand.

    Rick
     

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