Dan-O's first boat build. Small 8' Solar/Electric Cat!

Discussion in 'Boat Design' started by ElectroDanO, Sep 13, 2019.

  1. thepelell
    Joined: Oct 2019
    Posts: 8
    Likes: 4, Points: 3
    Location: italy

    thepelell Junior Member

    here is the unhappy foam guy :)
    the foam had several design flaws, so you could learn from my mistakes:
    - weight. being solid xps foam with plywood inside andtop/bottom + complete glass , they ended up heavier than an equivalent 4mm ply construction.
    - no rocker at all. Bottom was straight from bow to stern. Add that my bow was not really hydrodynamic and i had full stern,I guess I was dragging too much.
    - too narrow hulls for the weight. at only 15cm wide hull, my draft was around 12cm , and I guess that its useless to go long and narrow if you then go too deep.. better to be wider and shallower (think about SUP boards.. they are not narrow and long, yet you can paddly them with ease).
    I don't think that wave interference will be a problem at 4-5 mph, and from my experience with a 55lbs trolling motor, that is the absolute maximum you can achieve with those motors on any boat.
     
  2. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    On Post Number 252, here are some ways to squeeze more speed out of a trolling motor

    Efficient electric boat https://www.boatdesign.net/threads/efficient-electric-boat.27996/page-17

    Also, I have been able to double the power of an existing trolling motor by running it at double the voltage, way back when I first started my electric boats Hobby. The motor will not burn out if you keep the amps draw below the maximum rated and this is done by substituting a propeller of lower pitch and/or diameter. I ran a 12 volt Minn Kota for many years at 24 volts bypassing the five speed resistor speed switch with an external speed control and it showed no damage when I disassembled it for inspection. But that might only give you a a little bit more speed ( I got 6 mph with a 12-foot streamlined cat hull) if you are already at Hull speed.
     
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  3. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Here is a link to the fastest cat hull that I converted for one man seating and powered by a troll motor, at 12 volts I got six knots:

    Supcat - The innovative stand up paddle board https://www.boatdesign.net/threads/supcat-the-innovative-stand-up-paddle-board.54982/

    Descriptions on posts 11 and 17. I never saw any evidence of wave interference between the Hulls, but it might have been because the Troll Motor pushed water from between the two hulls which had a straight line shape on their inside surface.
     
  4. ElectroDanO
    Joined: Jul 2019
    Posts: 12
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    Location: Smyrna TN

    ElectroDanO Junior Member

    Man, I didn't know there was going to be this much to figure out on this project. Yikes! Since my paddle boat works so well, I wanted to stay with that basic design but make the entry and exit smoother, better length to beam ratio, ditch the dragging paddle wheel and have a center mounted motor. I would think doing those things would bump the performance up quite a bit without giving up stability. The measurements on the paddle boat hulls are 14" waterline beam by 8' long and the boat is 5' wide. That little boat is rock solid in the water and I do not want to lose that. That's where I came up with the measurements of 12" water line beam by 12' long and 5' wide. My thinking is, if I give up a little water line beam and gain four feet of length/displacement, draft and stability should still be as good(or better) and performance will improve. I guess I should do the math instead of just guessing. Sorry, I don't mean to sound stubborn. Maybe I am...o_O

    Again, I'm not fully against a mono hull. It just seems to me that a displacement mono's wetted surface and stability would be horrible compared to a cat. I've tried to research "trapeze bottom" but haven't been able to come up with much info. I'll keep looking.

    I've had a blast reading about and playing with with this trolling motor stuff! So much more to do but this paddle boat is a brick wall at the moment. Got to get past it!:)
    [​IMG]
     
  5. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Have you had any speed improvement with your modified motor? If you need more power, you might consider going to 24 volts on your motor, with a different prop.

    It might be a good idea to Mount the motor in a position where the prop can be reached for clearing weeds. Model airplane propellers are not weed-free and you may have more frequent weed clearing stops than before when you were operating with the stock propeller.

    Myself likes steering by turning the motor, rather than using a rudder. But I have situations when running River Rapids where precise steering at low speed is necessary- to avoid fast approaching rocks and overhanging tree limbs. A Rudder will just not work well enough while drifting in River current especially in situations where you have to spin around in only a little more than a boat's length.
     
  6. ElectroDanO
    Joined: Jul 2019
    Posts: 12
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    Location: Smyrna TN

    ElectroDanO Junior Member

    Oh man, once I started plying with this motor, I was hooked! I bought a ton of different props and have tried them all. Yeah, I gained a little bit of speed and a LOT of efficiency. Fun stuff! I'm not stopping now!

    I run in a good sized lake and haven't had any trouble with weeds. I'll keep that in mind though.

    Yeah, I would love to build a nice looking deck and set it up with a steering wheel and just use the motor to steer. How cool would that be!
     
  7. ElectroDanO
    Joined: Jul 2019
    Posts: 12
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    Location: Smyrna TN

    ElectroDanO Junior Member

    Got any pictures or info on this boat?:D
     

  8. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Dano, I disassembled the boat for transport and is in storage and for sale to anyone that wants to come and get it, the shell picture was previously linked. The specifications and pictures including cross section are on the page below, for XS speed at 40 lb and 10 ft length epoxy Hull ( error listing it as 12 foot, but that was sometime around 1995 as I recall).

    The XS SPEED SurfCat: A catamaran-styled windsurfer http://cctexan.tripod.com/xsspeed/index.html

    A low-slung beach chair was fastened on top for seating, and a standard 12 v Minn Kota 40 lb thrust with stock propeller was used, speed was checked with a sailboat knot meter. Too small for your project, but there may be some ideas that could be used for your bigger boat.

    Only used it a few times, it was meant to be used for competition in an Electric Boat speed and range event, but it never happened. After the event I had intended to cut the two hulls apart, and make a wider and more practical passenger collapsible hull, which could be adjusted to different widths for studying and tuning to Hull interference and stability effects vs. width. Never got around to that part, as got busy at work and lost interest, then I went into some other hobby projects.

    Current fishing boat trolling motors have the motor in front of the prop, causing turbulence and blocking free flow of water to that prop, which really degrades efficiency and speed. I experimented with Electric Power using long tail Motors of the type used for racing in Asia, and found them to be much better at efficiency and speed, for same power input. I have one of those in storage that is for sale also, for anyone who wants to come and get it.

    That tinkering brought me to the very efficient flex shaft design similar to The link in my post number 7 above, with almost no blocking interference to the propeller, which is what I use now.
     
    Last edited: Jan 23, 2020
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