Advice on shaft, seal, bearings for wooden kayak

Discussion in 'Propulsion' started by xellz, Nov 26, 2017.

  1. xellz
    Joined: Jul 2017
    Posts: 79
    Likes: 3, Points: 8
    Location: Japan

    xellz Junior Member

    I got plans for Plywood Boat Plans http://www.jemwatercraft.com/proddetail.php?prod=CFSOT and planning to power it with 12v 600w, 3000rpm electric motor using shaft, i.e. keep battery, motor, cables, electronics well protected from water (but want to keep room for up to 1kw just in case). But after searching for a while i'm not sure how to accomplish it.

    What is adequate shaft diameter? Is thrust bearing necessary at such power?

    How to seal kayak from water, when i searched for smallest shaft seals all i found was up to 20mm, which feels over sized for my needs. Small parts i would prefer to buy from ebay, most likely will end up cheaper than buying from japanese shops and more easy to find.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    If you are looking for economy a trolling motor is the best option. You can extend the shaft and keep the electric motor inside. They already have all the controls in a waterproof housing. Also, there are thrust bearings installed. You could use lip seals that are made in any size you need. https://www.parker.com/literature/Engineered Polymer Systems/5350.pdf
     
  3. xellz
    Joined: Jul 2017
    Posts: 79
    Likes: 3, Points: 8
    Location: Japan

    xellz Junior Member

    Two main reasons why i'm trying to go with shaft, efficiency and i want to try installing inboard system myself. Since it's small scale, should be doable and can learn a bit from this experience. Rudder is also nice to have when drift fishing.

    From what i learned trolling motors are quite inefficient. 735w brushless trolling motor is about 750$ with shipping from China. Quite a bit more bulky compared to trolling motor, but more efficient 600w brushless motor is about 100$ with shipping. Shaft is around 200-250$, need to decide on thickness, prop something in 100-150$ range? Lip seals seem to be rather cheap. What else will i need? Shaft log, strut i'm not sure, might try to do myself. PWM controllers are cheap, but waterproofing might be a challenge.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

  5. Irie
    Joined: Jul 2016
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    Location: Usa

    Irie Junior Member

    Hi xellz, I would have to agree with gonzo that a trolling motor would be the easiest and cheapest route. You could easily fabricate a mount on the stern so the trolling motor could still tilt out of harms way when launching and landing. An inboard setup would be vulnerable in the event your "landing gear" were to fail.

    That said, I can understand the desire to build your own drive. I used a 3/4 inch shaft, 3/4 inch cutlass bearing, and 3/4 inch thrust bearing on my electric surface drive. I used shaft packing inside the torque tube and a rubber boot (for roof penetrations) to seal the hole in the transom. It worked well, but please bear in mind my boat was on a very small lake, not the ocean. As for a prop I bought a used one from eBay for $30 and modified it to suit my application.
     
  6. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    You could install the trolling motor inside the boat and add an extension to the shaft. However, the idea of a kayak with a shaft protruding off the bottom doesn't seem to make sense.
     
  7. xellz
    Joined: Jul 2017
    Posts: 79
    Likes: 3, Points: 8
    Location: Japan

    xellz Junior Member

    I tried to compare, but trolling motors are cheaper only at low power output. I'm afraid 30lb thrust brushed trolling motor will be nowhere enough. Considering efficiency, shaft with decent brushless motor should provide more range at same power used, but by how much i can't really tell. In case i'm wrong about power required, inboard motor can be exchanged to higher output at low cost. There is certainly little to no info on shaft use on kayak size/shape boats. Another problem with stern mounted trolling motor would be that prop can get out of water in some conditions. Time to time i meet such conditions that on my Hobie Revolution 13 going through waves rudder is often far out of water and i'm helping steering with paddle.

    Deep waters, no weeds should allow shaft use without any issues.

    Half the reason, why i'm attempting to build such kayak is for learning and fun. I really enjoy making something unusual and didn't have the chance to make anything interesting in quite some time. So i'm really looking forward to this project and hope to start after new year.
     
  8. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Pickup a 100(+) pounds of thrust trolling motor, instead of playing with the dinky 12 VDC versions.
     

  9. xellz
    Joined: Jul 2017
    Posts: 79
    Likes: 3, Points: 8
    Location: Japan

    xellz Junior Member

    I thought about 80lb trolling motor in case i can't find all parts for shaft installation or won't be sure i can install it properly. Shaft for practice, learning and aesthetics. Efficiency is a bit difficult question, but seems shaft should get me some extra range and speed.
     
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