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Thread: Time to start to look for a prop

  1. #1

    Time to start to look for a prop

    OK
    I would like to look for a prop
    I'm gong to use a high speed trailer hub and spindle.
    It is a 5 on 4 hub I believe
    I found out my snowmobile clutch drive starts out at 3
    to 1 reduction and goes to 1 to 1.
    It kicks in at 1700 rpm
    I think I would love to run the VW motor at 2500 to 3000 rpm
    I'm not looking for speed 15 mph would be perfect.
    I live at around 5000 feet elevation.
    Over half the time I will be running at 32* or colder .
    I think with the standard carb and all, 50 HP is as good as I can hope for, Max.
    I plan on ordering a prop from "Arrow" but would love to get something used.
    BUT have no idea what To look for.
    Length?
    Pitch?
    I think a two blade wooden prop?
    Help
    Thanks CRU

    Last edited by Coyotes-R-Us; 09-22-2016 at 07:37 PM.

  2. #2
    Administrator Papee's Avatar
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    Re: Time to start to look for a prop

    Most props are designed to work best between 2700-3000 rpm. I'm not seeing any benefit at all running a reduction drive at your targeted rpm. I have no experience in how the snowmobile drive works but thought they are progressive. Is there any way to keep it from running 1:1? Your have to run more rpms to get the prop to run at 3000 otherwise you may as well run direct drive.
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  3. #3

    Re: Time to start to look for a prop

    The way I understand the drive, As the resistance decreases, the closer it gets to 1 to 1.
    I'm hoping to be able to get a bigger prop turning up to speed as it increases to 1 to 1
    Like low gear. I hope the motor will be able to maintain the rpm once it gets spinning.
    The exact # is .69 to 1 slightly an overdrive

  4. #4
    Administrator Papee's Avatar
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    Re: Time to start to look for a prop

    If that's the case I would expect one of two things to happen. It would go pretty much 1:1 right away because of the pitch of the prop. It would turn the prop up fast then turn to 1:1 at top end but you're still turning 1:1 so there is not mechanical gain as far as reduction so you could only turn a prop the same size as direct drive. Unless I'm missing something here. ANyone else have thoughts?
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  5. #5
    Super Moderator Corky's Avatar
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    Re: Time to start to look for a prop

    50hp is still 50hp no matter how you sneak up on it..If the finished ratio is 1:1 run a direct drive and be done with it...Keep it simple...A prop that's bigger than what you would use with a direct drive won't do any good when you hit the final ratio...Spinning the prop's mass is'nt the problem..The problem is having the hp to spin the prop to a certain RPM...A big prop will make the combo act like a huge slipping clutch and when {or if} it hits the final ratio it'll bog the engine down below what's going to be acceptable...

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  6. #6

    Re: Time to start to look for a prop

    What kind of RPMs are you guys running your motors?
    To get 2500/3000 rpm on the prop you have to be going
    5000+ on our motors with a reduction. Correct?
    So aside the clutch what size pitch do I need to be looking for ?
    Like I said Speed is not the end result I'm after.

  7. #7
    Super Moderator Corky's Avatar
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    Re: Time to start to look for a prop

    What you're asking for in prop selection is'nt as easy as it appears......The bigger props that are spun with a gear reduction are designed for a lower RPM for maximum thrust...


    Here's what I'm worried about with your set-up using that clutch:

    You're not worried about maximum speed I understand that but even at low speed say running 3-1 ratio the engine is revving 3 times as fast as you'd need for the same low speed using the direct drive...You'll need to "flash the clutch" just to engage the prop for even small manouvers.
    In other words you'll be reving the engine with little gain in movement before the clutch changes the ratio for EVERY small adjustment in speed or turning at low speeds...

    You've said the clutch progresses as the torque{resistance} decreases but you'll experience the most resistance as the prop picks up RPMs correct ???

    And lastely, it's anyones guess as to what spinning mass value was used for calculating the snowmobiles movement-to-rev ratio...In any case you're now replacing all that with a prop and it's resistance to the wind...It's going to be a trial and error process so be prepared for a prop swapping event until it's figured out...

    I'm certainly not trying to talk you out of using the clutch I'm just shedding light on all aspects of getting this clutch to work reliably and effeciently if you go this route...
    Last edited by Corky; 09-25-2016 at 11:55 PM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  8. #8
    Administrator Papee's Avatar
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    Re: Time to start to look for a prop

    Choosing a prop is a tough process to begin with. If you start with a known horse power it makes it a bit easier going by what others have done. Even the same engine may give you a different result depending on engine wear. When starting with an unknown setup it is best to start off with a cheaper prop that has pitch adjustment. I have had a VW setup and going with a reduction drive on it is certainly a step in the right direction. You need something to take the pressure off the seal, they didn't do well direct drive because of the lateral pressure on the seal making the leak.

    I wouldn't give up on the clutch idea, if nothing else you could lock in a reduction setup that would work for you. Maybe put in stronger springs to lock it before it gets to 1:1.
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  9. #9

    Re: Time to start to look for a prop

    OK?
    I just don't even have a starting point .
    I know absolutely nothing , NO experience with this in any way.

    Papee
    I have had a VW setup and going with a reduction drive on it is certainly a step in the right direction.
    What did you push your motor to rpms
    I did read they top out on HP at around 3000 rpm.
    Your prop was ????
    Thanks guys

  10. #10
    Administrator Papee's Avatar
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    Re: Time to start to look for a prop

    I had that boat about 35 years ago and don't remember specifics. I wouldn't think a stock VW motor would turn much more than the 084 turns, they are about the same hp. I"m turning a 58x28 prop right now but can only spin it at 2600 rpm. That would most likely be a good start for a VW motor if it is in good condition. Now adding a reduction drive I have no idea. It all depends on the motor and redrive ratio. You are treading in unknown area so you're going to have to experiment.
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  11. #11
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    Re: Time to start to look for a prop

    I always try to keep an open mind when I read the posts on any forum as I certainly am not the all-knowing expert but I have read about trying a CVT on several different threads and I always get to thinking how it would work (human nature i guess).

    There are a couple things that aren't adding up for me with what you are proposing. As I understand things 1.the faster you spin a prop the more load it produces, 2. as you apply load to a CVT (snow machine clutch) it decreases the speed of the secondary while allowing the primary (engine side) to remain at the same speed (hopefully max HP producing rpm). 3. if you have enough HP to overcome the load the CVT will upshift to "top gear" 4. to produce max thrust (load) with a prop you must spin it to max efficient RPM (depending on diameter anywhere from 2500 to 3100 rpm)- So unless you have enough engine HP at the Max prop RPM to create the max thrust, I don't see how a CVT will cheat you into making that Prop RPM. If you don't have the HP, the prop, will just add too much load to the secondary and the CVT will "down shift" never allowing the secondary to reach "top gear" or max prop speed.

    I just don't grasp the advantage of adding this weight to the setup.

    I'm sure someone can add to this and explain it better, or correct any mistakes in my thinking. Like I mentioned at the top, I've thought about this a bit and this is kinda what i came up with..... Any help?
    Last edited by dr.peck76; 09-26-2016 at 07:02 PM. Reason: missed point

  12. #12

    Re: Time to start to look for a prop

    Kinda .
    I'm going to consult with the prop people too." Arrow"
    In my Mind I'm Looking to spin the largest Prop the Old
    VW can turn.

    Hoping to find a Used prop first to try first.
    I don't even know what I don't Know.

    SO every thing I have read here and all over the NET.
    Sounds like If I find a 2 blade wooden prop like 60" and 26 Pitch
    It would be a good starting point . Correct ?

    I talked with a guy that's has a 69" aluminum prop off a Cessna plane.
    But knew little about it. Like if it is adjustable pitch.
    The picture has the spinner cone on it...
    $300 + freight.

    Anyway to make that work ?
    THANKS
    Last edited by Coyotes-R-Us; 09-26-2016 at 07:50 PM.

  13. #13
    Administrator Papee's Avatar
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    Re: Time to start to look for a prop

    An airplane uses a tractor type prop. You would have to mount the motor backwards to use that prop. This means the engine would be at the back of the boat and the prop in front right behind you. This would take half the boat up till you get a cage around it. Then there is the position of the prop, it would be 3-4 ft away from the transom and cause all kinds of trouble with part of the air hitting and being trapped by the transom.
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  14. #14

    Re: Time to start to look for a prop

    YUP your right. Did not think of that


  15. #15

    Re: Time to start to look for a prop

    Do you think a 60" 26 prop would be a fair guess ?
    Room wise I think I can go about any size prop.

  16. #16
    Administrator Papee's Avatar
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    Re: Time to start to look for a prop

    That should be pretty close for the VW engine running direct drive. If your reduction works at all it may be a little small or under pitched. It will certainly give you an idea what you have. I think Doozit had one pretty close to that for sale. If you can find a used one cheap it would be worth a try. You can always pass it along if it doesn't work for you.
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  17. #17

    Re: Time to start to look for a prop

    Cool thanks
    I'll PM him

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