The "water bug" a work in progress...

Discussion in 'Everything Else in Montana & Beyond' started by d4570, Dec 8, 2015.

  1. d4570

    d4570 Active Member

    I'm in the beginning proses of building My Mini airboat I'm calling the "Water Bug".

    At this point I don't have a hull, but have an idea what I want. Around a 14' very flat ( mud) Bottom Jon that I would put out riggers on or Fabricate a catamaran type hull with FLAT tubes .

    Right now I have a 1971 VW Bug motor. 1600cc air cooled around 60 Hp.

    I got it running very nice, I still need to get a voltage regulator for the generator and a fuel pump.

    Right now I'm gravity feeding fuel , I'm going to go with an electric external fuel pump both on order.

    I'm in contact with a prop manufacture and am on hold .
    I am torn as to witch end of my VW motor I need to put my prop. Direct dive or reduced.

    Each would need a different prop size and direction.
    I finally got the little motor running nice, and it sounds strong, for 1600cc 50hp vw .
    .As you can see I had to put the starter on to "Back" of the motor and it sticks out about a foot.
    If I run off that end ,either direct or reduced it need to be past the end of the starter.
    The front ,belt end, I read that the bushing on the crank will not hold up to the strain of a prop.
    So I would have to reduce it Belt or chain.

    How come a person just could not add a chain Drive on to crank up to the generator and put the Prop on the generator ???
    Would a motorcycle chain hold up? Would the generator an stand holdup ?

    THOUGHTS ?





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  2. jbm

    jbm New Member

    for starters you will need to find out what prop over all diameter you have room to work with and what pitch. this will tell you how fast you can spin the center hub keeping in mind that your prop tip speed needs to stay under the speed of sound [ 340 mps ] so the prop does not tear its self up . a good area for the tip speed at wide open engine RPM is in the . 70 range. after finding all these #'s you can then see if the prop hub can turn the same RPM of the engines crank.
    most props can not turn that fast and this is where the reduction box comes into play . also like you said if you could bold the prop to the front or rear of the crank the vw crank thrust bear can not take that kind of prolonged thrust and will fair very fast. chain will work but again you will need to know what tooth upper and lower sprockets to use to get that max prop tip speed where it needs to be
    the vw engine sounds like it would be good for this type of set up with it being air cooled and such then you start to run all the specs on it and it soon starts to fade. power to weight is not very good on it when you look at so many other small high output engines that are also air cooled or running water/coolant to air heat exchanger. then you need to look at how you mount the engine high [ the cheapest ] or down low for better handling [ cost is higher ]
     
  3. jbm

    jbm New Member

    you would be much farther ahead with a set up like this with a belt and a small twin cylinder like in this pic
    much light for better power to weight ratio and they make all the parts for this type of set up so much less R&R on your part as they have already done it all and you save time and money
     

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  4. jbm

    jbm New Member

  5. d4570

    d4570 Active Member

    You are right on all points.
    BUT
    This is the motor I have.
    I have looked at the Using Glen-L plans, along with our Rear Drive System But Like most things
    It is WAY out of my price range.
    The one set up is a direct drive off the crank and I'm afraid I'd be working on thrust bearings ever season
    AND be under powered.
    I was talking with "Arrow" prop guys the will set me up with the right prop all I have to do is make a decision.
    I can get belt reducers made for just what I want to do but I'm going to have to do it red neck junkyard style.
    If it was just for water I don't think I'd have a big problem, relatively easy to push through and ice and snow
    should be about the same I would think . A smaller prop less pitch and on the front of the crank.
    I plan on using it more on half frozen and half dry rivers and lake beds a lot too.
    I need it to be able to move on mostly dry ground and gravel.
    SO I need to get every ponies and ounce of thrust I can get.
    The guys at the prop place said it would defiantly need to be reduced to be able to spin the biggest and most
    pitch the little VW will turn. A Big prop going slower is way more efficient they say.
    The bearings in the generator are very substantial and are used on many other industrial applications.
    There not what I was concerned about, Where it attaches to the top of the crank case .
    .The whole thing is made out of some kind of aluminum allow that is hard but brittle.
    I'm afraid the vibration and extra strain may brake the motor...
    Anyway
    I'm always looking for input like yours thank you.
    Still designing in my mind, what do you think about a snowmobile clutch belt drive ?
    Or using the VW clutch and a drive shaft off the flywheel end to a carrier bearing then to a reducer?
     
  6. jbm

    jbm New Member

    sometimes working with what we have because it was cheap or free can end up costing even more in the end
    your stock vw case is not aluminum even if it looks that it is magnesium and boy does that put off some very pretty colors in the flames when it takes off
    also keep in mind when you look up parts vw engine in an air boat and they list them as bolting to the front or rear of the engine make sure which side they are talking about
    on a type 1 vw engine the pulley is the rear and the clutch/flywheel is the front
    belt drive will be the easiest to install and get the reduction ratio right also the belt drive will not be loud like a chain drive will be
     
  7. d4570

    d4570 Active Member

    Thanks ,good to remember.
    I know the belt system would be best.
    What do you think of my idea of the vw clutch / drive shaft charier bearing thought ?
    If I can't get what I want with what I have, I'll get rid of it and do something else.
    Been a junk yard red neck for a LONG time.
    Some times it works great some times not so much, all part of the fun .
     
  8. jbm

    jbm New Member

    why would you run a clutch ? just more parts to add to cost and more to go wrong. you will need to run a reduction unit i am sure to keep the tip speed at WOT RPM in the sweet spot. again belt is the best for that with your set up. your air boat will be set much like a jet just moving air instead of water. the impeller tip speed on a jet boat must also be in the sweet spot at the engines WOT RPM with most inboard jets being a 1 to 1 ratio we do this by using small or larger diameter impellers. we can then also control this wot rpm with the pitch of the blades on the impeller. this is why the smaller high rpm marine engines used in jet boats will have a max OD of 155mm . we can also control slip by adding another stage from 1 to 2 or 2 to 3 stage and last we can change the nozzle size . all these have to work together or you can really end up with bad performance in a jet. the same will happen with a prop in an air boat. you will need to know your engines hp and what your max wot rpm will be. this will tell you what your reduction ratio will be. then your prop OD and blade pitch and size and how many blades
    then you can also get into counter rotating props that can give you even better trust with the same hp
    looking at your vw engine you have there it looks like it is a dual port head so that is a plus if looking to add more power. to bad it not a type 3 with EFI
    like this 68 type 3 fastback
    BTW this make model and yr was the very first mass produced auto sold in the USA to come stock EFI
     

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  9. d4570

    d4570 Active Member

    Only reason I'd use the clutch is to have a way to hook up the motor, crank shaft
    and move the prop farther away from the starter.
    These old VW motors are like an 870 or a 10/22 you can get ANY thing after market for them
    Yup the prop guys explained that to me.
    I have a jet boat and kinda under stand .
    PS the prop is going to be a two bladed wooden prop.
    A three blade carbon composite would be wonderful and I could change the pitch if I needed too.
    But there again. $1500 compared to $400 well you know...
     
  10. jbm

    jbm New Member

    you need to open that wallet up and let the moths out lol $1500 is nothing when you start to get into air boats
    the guide that runs on the river we hunt caribou on runs an air boat and last time he stopped and talk with us he had new carbon fiber counter rotating props that cost him $36,000
    if you go to that website i posted with vw air boat parts you will see you can buy the complete set up for your engine and it really is not a bad price
    and you starter will have a real mounting location that you wont have to worry about it falling off
     
  11. d4570

    d4570 Active Member

    It's open as far as it will go ....
    I wish there was more but I want to eat this week too.
    I'm glad your buddy can get a $36 grand prop .
    If I could I PROBABALY wouldn't be using an old 1971 used bug motor
    Just saying
     
  12. jbm

    jbm New Member

    not sure he is my buddy just a guide on the river making a living . he seems to know that you need to spend money to make money :)
     
  13. d4570

    d4570 Active Member

    Not trying to make $$$ just trying to have some cheap fun Man.

    I have a line on a snowmobile clutch drive ( torque converter )

    Maybe I can make it work off the Flywheel end and off set the prop to avoid the starter.

    PS
    just got the Voltage regulator and installed. Works.
    The Fuel pump came too No more gravity feed
     
  14. Firstly, i have no idea what you two are talking about, second, i wish as a fishing guide i earnt $36k per year!
    Cheers
    Richard
     
  15. jbm

    jbm New Member

    hi richard
    i think that guide made a bit more then $36k . this was up in alaska and at that time i think he was $3500 per person just to drop you off up stream closer to the caribou. he also does full guided hunts but no idea what those cost . we take our own boats to run the rivers. cant afford to pay for those trips like like
    here you go D a look at what its like to air boat on some of those braided rivers its also a pretty tricky river to jet boat

     
    devon flyfisher likes this.
  16. d4570

    d4570 Active Member

  17. d4570

    d4570 Active Member

    I just picked up an old Johnson skee horse ( Free with 2 new drive belts). It is complete with the belt drive and chain drive.
    I'm going to try to use it to drive my prop off the flywheel end of the Bug motor.

    The 2 stroke motor was really slow turning around 4000 rpm That's is near what I expect out of the VW , more like 3000/3500 rpm
    Back yard red neck mechanic
    "D"
     
  18. jbm

    jbm New Member

    if i am reading you right you plan to use a primary clutch with a belt to a secondary clutch that will then turn a sprocket that will have a chain to a bigger sprocket
    is this right ?
    if so the clutch will be nice in that the prop will stop turning at idle but not really needed if it is inside a good cage
    then you will need to break out the old slide rule to come up with you WOT RPM on the type 1 engine should be around 5000 rpm
    at the crank/primary clutch . if the clutches are set up right for the rpm you plan on running the engine it will be over driving the secondary clutch . now at wot it is pretty easy to see what rpm it is driving the secondary clutch. i would use a handheld laser tach . after you get that you can do a little math to find how fast you want to drive the smaller sprocket that is turning the prop. make sure you know what max rpm the prop that you end up getting is
    let us know when this is up and running
     
  19. d4570

    d4570 Active Member

    Yes that is the plan.
    It'll be a wail ,but of course, The pictuers will flow.
     
  20. d4570

    d4570 Active Member

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