Adding an inboard to kayak?

Discussion in 'Boat Design' started by FishinCary, Dec 31, 2019.

  1. FishinCary
    Joined: Dec 2019
    Posts: 16
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    Location: US

    FishinCary Junior Member

    FD3A5204-1FD3-4D78-9362-FB5018A6873D.jpeg Hello,

    What an active resource. Hoping to leverage your expertise to save myself mistakes that cannot be undone. For example, ruining a classic boat. You’ll find I’m perfectly okay with you telling me my ideas are horrendous. No offense taken, as I know they are likely stupid. I’m here to learn and then actually implement a feasible build - which I promise to report back on. That said, I’d appreciate suggestions on alternatives if the inboard idea is just too insane.

    I am interested in advice on adding a gas motor to my 17’ kayak. It’s an Eddyline Orca 17. A fiberglass/Kevlar kayak from the early 80s that is my pride and joy for striped bass fishing. I already have a stern mounted electric pod drive (Bixpy) on the rudder that pushes the boat 1.5 mph (14 mile range) up to 5.5 mph (7 mile range). I’d just like a gas motor to get more range. I don’t care about speed as much. It’s a 17’ displacement hull with a keel. The stern is a good 7’ behind where the rider sits. This boat isn’t gonna get onto plane regardless of how much power I stick on it (I think). When I paddle as hard as I can, with the motor on, I can get it up to 7mph. So I am hopeful that it may do 8-10 without even getting on plane. That said, I’d be happy even with just extended range at 5mph. Buying more batteries is an obvious option. But at $570 per battery and 75 minutes at top (5.5mph) speed... I do not want to go this route.

    Boats got a 400 pound weight cap. I plus my gear am 225 tops. So we have about 125 pounds to work with.

    Regardless of what design I go with. I won’t be making it steerable. The rudder will serve as steering. The motor is just a drive.

    Side mounted outboard is the default option. Also looking at longtail and inboard but no sure if these are realistic.

    Side mounted outboard
    Pros:
    No holes below water line.
    Prop and shaft can be tilted up and out of water meaning I can launch without a ramp. Modular assembly keeps transport simple (can still stick kayak on top of car).
    Cons:
    I’m just not at all excited about this solution
    Gets in the way of fishing - since it will likely require some sort of outrigger arm to mount the motor on.

    Longtail motor
    Pros:
    No holes below water line
    Prop and shaft can be tilted up
    Modular
    Cons:
    Since the motor sits up high above the yak’s center of mass, I imagine there will be trade offs between power and stability.
    May not be possible for reasons of angles and mounting. The cockpit is a good 7’ in front of the stern. Then the drive shaft still has to clear the rudder which protrudes another 1’ from the stern. Would be a REALLY long shaft I imagine.

    So that bring me to an inboard. The main concerns being 1) can I reinforce a fiberglass kayak hull enough to take the forces involved 2) is it possible to have a modular drive and motor assembly (for transport). I know Mokai has a modular drive, but I’m an idiot in a suburban garage not an actual watercraft builder. So not so sure if this is a fantasy or something that could be done. If the motor wasn’t modular, then I think it defeats the purpose of a yak. Not being able to remove the motor introduces a tradeoff between power and weight that I’m uninterested in optimizing. I don’t want a yak I have to trailer. I also don’t want a motor so small that it barely pushes the boat (but is light enough to cartop).

    I want the inboard if it can be made modular. Just not sure whether this dream is possible or not.

    Best regards and thanks in advance for any advice
     
  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Considere a hybrid system. A small gas generator powering your existing electric motor. It could still be modularly portable.
     
    clmanges and Barry like this.
  3. Squidly-Diddly
    Joined: Sep 2007
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    Location: SF bay

    Squidly-Diddly Senior Member

    as a Prius Prime owner, I couldn't agree more. You seem happy with performance of existing electric setup, so if it ain't broke don't fix it. You can get little 20lb gas gen-sets for about $200, or Honda or Yamaha 30lb units for about $900.https://www.amazon.com/dp/B00P9ONS7...804088195be2d1c96ae2868be475de&language=en_US
    They look a bit tall, but IIRC most of weight is down low to prevent tip-overs, so shouldn't hurt your stability if you can place on floor of Sit-In "real" kayak. Maybe put little rubber feet onto 1/2 sliced pool-noodle to protect hull.

    If you just add a small generator, you can always go back to pure electric and use in restricted waters (and you wouldn't butcher your legacy boat). IMO even a cheap-0 off-the-shelf generator will be much safer than any home-made ICE installation. Plug-In Hybrid seems like better idea for recreational boating that cars, because with boating it would be really nice to be able to troll at low speed without any ICE noise (or smell). With road noise, its really not much diff in a Prius if you are in MV or EV mode.

    Since its not my money, I'd go for the Honda, because it will be so much nicer to be close to for hours, and probably less chance of it hurting your existing battery due to its "clean" power. Plus when you explain to your wife that your latest Big Ticket item isn't JUST for boating, but can also be used to power TV, cell phones, refrigerator and even small hair dryer in emergency and "its a Honda".
     
  4. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    You might be able to easily alter the Bixby design to give you efficiency and speed, seems like the least fuss and expense, if it can be done. Removing the existing cage around the propeller and substituting a more efficient propeller for the existing one might get you to your goals. A chap on this Blog has done something like that with a regular trolling motor.

    The most efficient system capable of high speeds and long range is probably a do it yourself long tail, a chap on this blog has built one that gets 3 miles per hour with only 30 Watts, for a very long range capability!

    Myself wouldn't like the noise or complications of a gas motor for my fishing endeavors.

    Torquedo probably has the range and you're looking for, but it would be very costly to switch over to that.
     
  5. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    It would be a crime against nature to add any sort of internal combustion power source. An inboard installation would be a PITA. It would add unwanted weight, necessitate having a prop shaft and exposed prop, would hamper the shallow water ability that the kayak is so good at. It would also stink and make noise.

    I have successfully driven my 16 foot sharpie with a 28 pound thrust troller. It would drive the 320 pound boat a bit more than 4 mph. (320 pounds included the skipper and fishing gear) I used a small battery like the one used for riding lawn mowers, snowmobiles, etc. A good battery of that kind costs about $70. My little battery was good for about 45 minutes at three quarter throttle. Two of those batteries were more than enough cruise time before I became tired of failing to catch fish. The trick is to use a smaller electric troller not a big one. Your 17 footer will have a hull speed of something like 5.5 mph and trying to drive it faster will suck the available amperage out of your battery in a hurry. If you must go faster, then the best deal is to get a different boat and put up with the noise and smell of a gas engine.

    You could even consider a tiny sail for down wind work while the electric motor rested. Not much more than a large umbrella will drive the kayak at a pretty good clip if there is some wind at your back. The umbrella also doubles as a shade making device when you are still fishing. It is also a silent propulsion device. Yes I have done that with my 15 foot kayak. It is even fun to play with.
     
  6. FishinCary
    Joined: Dec 2019
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    FishinCary Junior Member

    Thanks to everyone for the advice. I have removed inboard from the list of options. While it would be cool to build, I agree that it’s just not the right solution here.

    I really like the idea of the Honda inverter generator. Just need to talk to Bixpy and see if they think it’s better to have a single battery connected to the motor and generator (option 1). Or to have one battery charging and another to the motor (option 2).

    Fingers crossed they OK option 1. Total investment would be $900 for the generator. But not so sure the lithium battery will charge properly if there is a parasitic load. See How to Charge Li-ion with a Parasitic Load – Battery University https://batteryuniversity.com/learn/article/how_to_charge_li_ion_with_a_parasitic_load

    Option 2 isn’t ideal either. Though the generator produces enough current to theoretically charge the battery in 2-2.5 hours (20-40% ineffiency) the battery charger actually regulates the current such that it takes 4.5-5h to charge. So maybe I get 2 additional batteries and the generator. 2 batteries charge while I run one. 75 minute run time at full speed (5.5 mph), so I figure I could run them at like 4mph for 3h a piece and never run out of charge. Total investment $900+570+570.

    I agree with the final recommendation. For that kind of money (option 2) ima just save up to build a different hull shape. But if option 1 is possible I will report back on how that goes.

    Y’all are great. Thanks a bunch :)
     
  7. FishinCary
    Joined: Dec 2019
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    FishinCary Junior Member

    :D Brilliance haha
     
  8. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Will a dirty output from the generator affect the battery charging system in independent mode or speed control if used in float mode? Some of these generators may have a distorted shape and frequency for wave output rather than sine wave.
     
  9. FishinCary
    Joined: Dec 2019
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    FishinCary Junior Member

    Help me understand some of these terms. What does independent, speed control, and float mode refer to? The generator? The motor? The battery? Sorry I am just not that familiar with these things. I want to understand what you’re saying though.

    Regarding the imperfect sinusoidal current it’ll produce. Yeah it won’t be perfect but I am unsure how to tell what is “good enough” without just trying it and seeing if it degrades battery life. I reached out to the company for their input but they haven’t responded yet.
     
  10. portacruise
    Joined: Jun 2009
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    portacruise Senior Member

    Sorry, Independent mode equals option 2 where the spare batteries are charged separately from the battery driving the bixby motor. Float mode equals option 1 ie. Like the parasitic link you posted. Generator equals Honda inverter generator. Gas motor equals the Honda generator at this point, or maybe a small outboard motor before you had made the decision for a Honda generator.

    The imperfect sinusoidal electricity created by the Honda may not be compatible with sensitive electronic devices ( such as Maybe the bixpy lithium battery charger separate and not related to the parasitic load link issues?) as you have pointed out. Before using trial and error, it might be possible to check the ratings of the Honda to see if anyone had issues with running sensitive devices with the Honda, which might have detrimental effects anywhere between did not work to ruined equipment.

    In option 1, the speed control of the Bixby would draw Power from the Bixby charger first, before using battery energy and that might overload that Bixby charger, especially when traveling at high speed power demand. As an example, some of my unrelated battery devices recommend that they should not be operated while connected to the charger ie. Unplug before using.

    Excuse the revisions, difficult to put into written words.
     
    Last edited: Dec 31, 2019
  11. FishinCary
    Joined: Dec 2019
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    Location: US

    FishinCary Junior Member

    @portacruise yeah those would be my concerns too. My guess would be if charging in float mode (one battery connected to both generator and motor) works... then charging in independent (one battery for generator and one battery for motor) would too. Dunno if either will work though. Bixpy (company that makes the electric motor) used to respond to my questions quickly. They read my questions but haven’t responded yet. Maybe they’re consulting the engineers. Maybe they’re tired of my questions haha.

    Anyways I appreciate your suggestion to look for reviews of the generator as applied to charging other devices with a parasitic load. Maybe from those reviews I can infer whether it’s likely it would work with this Bixpy battery (a lithium battery). If the battery was just a regular lead acid deep cycle battery.... I’d have little doubt either setup would work. In that case the battery would charge if the current delivered to the battery exceeds the current drawn by the load, and vice versa. However given how finicky lithium batteries are with parasitic loads I’m not so sure it’ll work out with a single battery. Waiting on a response from the company that makes the motor and battery (Bixpy).

    Regarding this, I think you’re spot on. Wiring up the generator and load (motor) in parallel with the battery will likely produce this problem. After all the charger takes 5 hours to charge the battery. And the motor can drain the battery in 75 minutes. Likely something bad gonna happen if I set the motor to max while the generators going.

    It’s not looking too promising that either option involving generators and batteries would work. But I’m gonna hold off on nixing the idea until I hear back from the company directly. They’ve been quite good about allowing me to test their products in the past. Even sent a few free accessories a couple times. Hope is my questions pique their interest and they send me a battery to test it out with (and likely destroy lol).

    Finally, thanks to everyone for the input. This forum has been immensely more helpful than the other places I’ve asked this. Might end up side mounting an outboard if I can’t get the generator idea to work. But it was helpful to bounce these alternatives off you guys to figure out the details of each.
     
  12. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Instead of an inboard, how about a long tail mounted on deck? Then you're not violating the water-tight integrity of the hull, and the motor is in the open so it can breathe and cool. Check out Longtail Mud Motor https://scavengerbackwater.com/, Long Tail & Super Long Tail Mud Motors | Mud Buddy https://www.mudbuddy.com/category/long-tails, GO-DEVIL Longtail - The Four-Wheel Drive of Marine Engines http://www.godevil.com/products/longtail-engines/

    Since your biggest problem may be finding a motor small enough to be suitable for a kayak, another possibility would be a model airplane motor with an air propeller. You might be surprised how much thrust they can produce.
     
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  13. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    120 volts in a kayak sounds risky.
     
    FishinCary likes this.
  14. FishinCary
    Joined: Dec 2019
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    FishinCary Junior Member

    Amen! :confused:
     

  15. FishinCary
    Joined: Dec 2019
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    FishinCary Junior Member

    I definitely like this idea of a longtail motor more than I like the idea of having an outboard side-mounted. This seems like the winner given the issues with the generator idea (compatibility with lithium batteries, max charge rate) or the inboard idea (cooling, ventilation, mounting).

    I appreciate the many links you provided. Those look like excellent motors.

    Vanguard 6.5 looks good. Little heavy and pricey at 109 pounds and 2075 though.

    Scavenger longtail look a bit more modestly priced and a little lighter too for the same hp. Bout 75-85 pounds and 1300-1500$.

    I found a cheapest option. Do you have any experience with this brand? “SwampRunner mud motors” sells kits compatible with 3 and 6.5hp predator motors.
    Only would be 575$ for the 6.5hp at 84 pounds
    Or
    $510 for the 3hp at 52 pounds

    Home - Swamp Runner https://www.mudmotorkit.com/

    Kayaks got 400 pound weight cap. I and my gear is only 225 max. So theoretically could slap any of these motors in. But the high COM with a longtail makes me think maybethe 3hp is the only feasible one. Not so sure I wanna stick 80 some pounds too far above the waterline.

    Don’t wanna add outriggers for stability. Would add drag and get in the way of fishing. So without outriggers, is it reasonable to mount the 52 pound 3hp longtail on this yak? Gonna be some additional weight in adding some sort of motor mount in the rear storage area of the boat... in order to mount the longtail. So thinking got to go with the 52 pound (3hp) one... and even then it could be hairy stability wise.

    Keep it coming y’all. Thanks
     
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