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Thread: Fitting low water pick up to outboard engine

  1. #81
    phillnjack
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    you must have a different gear ratio to me. My engine has a 2.42 gear ratio i think !!!!
    if my engine did 7,000 rpm with a 24 inch prop with zero slip it would only run 65.7mph
    But mine im sure is limited to 6,000 revs, so that prop (if my engine could swing it)would
    give 56.34 mph with zero slip !!!!!!

    i realy dont have any low end torque problems with this engine, its like power all the way through.
    But ofcourse ive not tried to swing a bigger prop than the 19 sst that ive got on there at the moment.

    phill...........
    Last edited by phillnjack; 01-13-2013 at 04:58 PM. Reason: wrong numbers

  2. #82
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    Default help 60 70 75 hp johnson evinrude guys for phill

    Hi Phill,

    Now you will get lots of good input from lots of people I am sure!

    remember also with props that if its stamped 24 it may be actually 22,23,24,25 or 26 by some one elses pitch mesure. measuring pitch is very hard. I have bought a 19 pitch in the past that was actually more like a 24 when tested on boat taking the speed revs and gear ratio calcs. I think some of the 75hp stinger motors had a 1.86 to 1 gear ratio but I may be wrong.

    When you get that boat of yours set up and wound out you better hold on!!!

    I aggree with you in that the motor should be no set back on that hull, It will make it safer and your hull looks like it may want to porpous if set up wrong, My feeling is surface pierce but not to much.

    I would get the nose cone on, just use two part filler- forget the low pick ups. and if you can get your hands on some cleaver or chopper props to try in the 22 to 26 pitch range would be a good start. Remember you can always move the props that dont work on your hull out via ebay as I do (trial and error).

    Any 60 70 or 75 hp guys please add your info for Phill
    Glenno

  3. #83
    phillnjack
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    we are so limited in the uk as to props and finding different types etc.
    its only on ebay we find anything at all, not many race boat places and they dont seem to sell anything used.

    i keep seeing a particular prop on ebay,i missed a good one a few weeks back, and it went for silly money,
    the prop was a over hub 12.5 x23 omc stainless and made $80 us dollars.
    i could of kicked myself for missing that one, but the michigan is still on there for about $110 buy now.
    It says Michigan Part no. SS0523, but i cant find any info at all on the prop so might leave it alone,nobody
    else seems to want it and it says brand new still in box but old stock.
    when i see the props by ron hill they look so good,proper master pieces of artwork, and that raker on
    your 75hp realy look the business.

    i am going to try and see if i can get a transom lifter fabricated that only gives me about 2 - 3 inch setback to
    try and keep it close.
    I dont know what to think about a long setback as never used one at all.
    Plus the longer the setback must put more strain on the transom,especially with a lift as well ????



    phill

  4. #84
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    Your boat does'nt need a nose cone, your best max height is probably going to be 2-3 inches up and a 21 inch raker or renegade. The single cable steering and sitting on a plank is going to make it enough of a challange as it is.

  5. #85
    phillnjack
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    The engine is only being operated with single cable for now to make sure the motor was going to be ok.
    I should be picking up some hydraulic oil this week and then the hydraulic steering system is going on.
    The steering ram end is a morse C3000-OB heavy duty and the matching helm to go with it.
    I prefer to have hydraulic steering due to more precise steering, plus i like the idea of straight ahead if
    i want to let go when going slow etc.
    My hydraulic takes about 3 pints of oil to fill, so im buying a gallon of aeroshell 41 from an airport,its the
    same stuff just a lot lot cheaper than the teleflext/seastar/baystar fluid just with a red dye for aero use.

    I hope to get the hydraulic oil and give the system a test this week then if all is well i will cut the large
    hole needed in the consol to take the helm unit.
    The morse hydraulic system i have (so ive been told) is rated for upto 300hp.
    I think this steering system should be ok for my boat, i hope it is anyway.

    Name:  Helm unit teleflex.jpg
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    Name:  hyd steering  ram .jpg
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    Obviously i will be re-spraying the helm unit and ram housing before they go on the boat to
    keep the parts from getting attacked by fresh or salt water.


    The engine sitting on a plank ???????
    Oh no, if i get a jackplate fabricated it will be from stainless and will encompass the transom with
    a welded hollow block on top, it will all be made of around 3/8th thick 316 stainless steel.....



    phill..

  6. #86
    Team Member Jfarrelly's Avatar
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    Where did you get or how'd you make your nosecones/low water pickup

  7. #87
    Administrator Ron Hill's Avatar
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    Default I Have Wanted To Make A Gearcase

    Quote Originally Posted by Tim Kurcz View Post
    How about water pickup at the bottom of the skeg? This allows positioning of the gearcase bullet at/above the water, eliminating drag almost entirely without risking loss of cooling water. From that position, all prop theories can be safely tested.

    Tim
    My dad made my brother a gearcase for his "A" Hydro in 1949 and my brother beat 32 "A" Hydros in the Hearst Regatta.

    Because gearcases are in my DNA, I have wanted to make a stainless steel gearcase and part of that concept was to have the water pickup in the skeg.

    A stainless steel gearcase could be made very thin and the skeg could be larger but thinner...

    Maybe, in my next life Tim.

  8. #88
    Team Member zul8tr's Avatar
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    Quote Originally Posted by Bill Van Steenwyk View Post
    Lets pretend the prop has NO FUNCTION as far as propelling the boat thru the water, other than the fact it is there in it's normal location, on the prop shaft, and in the water. In this visualization, propulsion is being achieved in this example by ANY other means you might imagine EXCEPT the propeller. Could be water pump, sail, oars, or any other type power that will move the boat forward through the water EXCEPT that prop on the motor.

    Now imagine it raised on the transom so only a part of one blade is in the water at any one time.

    Now imagine it lowered on the transom so ALL of the blades on the prop are completely submerged in the water at one time.

    Which location of the prop (depth in the water) do you think will give you the best speed, all other factors remaining the same.

    Same thing applies when the prop is driven by an engine and that prop is the sole propulsion for the boat. The more blades in the water, the more DRAG. It also may be easier to imagine the prop as a complete disk. The bigger the disk the more drag. If the disk has holes or slots cut into it, drag will be reduced. That is also the reason a jet airplane is faster (among others) is an airplane with a propeller generates much more drag than one without. Add more propellers (think 4-6 engine bombers) and more drag. In addition, the tips of the propeller reach supersonic velocity while the vehicle itself is much below the speed of sound, also leading to propeller inefficiency. That and drag is why a prop jet is slower than a pure jet.

    There is much more to it than just this, just as air is much different than water insofar as the way it acts when moving through it with a propeller or any other object,and that is where number of blades, pitch, diameter and other factors enter into the equation. BUT one of the large things to effect a prop (or any other object moving thru air or water) is DRAG. This is also the reason that some still run props with only two blades when racing, although not a lot anymore. If water conditions will permit, a two blade will probably be faster (taking into a lot of other factors) than a multi blade prop, especially when you are running a surfacing type prop, is there is LESS DRAG with 2 blades than 3 or more. This is not always true, depending on handling problems you might encounter in rough water, etc. You can raise a multi blade prop higher out of the water and have the boat have better handling capabilities because of that word again, DRAG. Eventually you get to a point where handling and prop efficiency become more important than drag reduction, especially if you can not control the boat anymore because of lack of directional control which the lower unit/prop combination in the water give you.

    Unfortunately there is no magic formula which will allow you to calculate this point. The only formula is testing and good record keeping.

    Hope this helps.
    Although this thread is a bit stale I figured add'l info wouldn't hurt.

    Bill is right about the theory he presents above for the working part of the prop in the water with low air mix doing the thrust work.
    Back in my racing/experiment days with 1:1 gears on a Quicki H tower using 2 cylindere Merc with a 2 blade prop I was searching for more speed. To get it I would syncro the prop to the piston position by trying different spline positions of the drive shaft to the crank. What worked the best for more rpm and speed (about 1 mph which is a lot in a race) was to get the prop blade to dive at about the 9 o'clock position (looking forward) with the piston at TDC (not many choices with the limited spline numbers but it can be done). Never played with this using 16:21 gears and 2 blade props & 2 cylinder engines, figured it wouldn't help due to the cyclical nature of blade feed to TDC position. Also indexed the plugs.
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  9. #89
    Team Member ice_spy's Avatar
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    Again, thread may be a bit old but I'd like to give my stance on the 100 view car crash.
    From my understanding on propellers, it is like a screw. The pitch varies the amount of travel, the gear ratio and amount of prop slip (no or less drive) also factor the amount of travel forward in one rotation. Drag is a big factor here, ive never seen an efficient submerged race prop on a race boat for a reason. The other term mentioned is piercing. Surface prop or surface piercing is definitely two names used. When it comes to submerged boat props, most designs are very similar with the exception to allow some cavitation with less slip. This design comes into greater play when two most common surface props are used. Chopper and cleaver design. Each design although both surface type props offer different results. Choppers are known for bow lift and cleavers for stern lift.
    As said, i also believe that 1 blade is most efficient in drag as obviously none would be best for drag. You cant run 1 blade for ballance reasons therefore 2 is the next best. Im not goin into conditions and hook up other than obviously race props with more blades like 5 on F1 tunnel is too hook up better and smoother, but like when going from a 3 blade to 4 on a fishing boat, it lowers rpm.
    So to go faster, you need more pitch, to run more pitch you need less drag, to have less drag means you have to higher. Too high the amount of drive is lost. The prop design is tested and made to run at this happy medium. No submerged prop has been invented to run at the same effectiveness as surface drive with the same amount of power/ boat set up etc.
    The race never stops

  10. #90
    BoatRacingFacts VIP John Schubert T*A*R*T's Avatar
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    Quote Originally Posted by zul8tr View Post
    Although this thread is a bit stale I figured add'l info wouldn't hurt.

    Bill is right about the theory he presents above for the working part of the prop in the water with low air mix doing the thrust work.
    Back in my racing/experiment days with 1:1 gears on a Quicki H tower using 2 cylindere Merc with a 2 blade prop I was searching for more speed. To get it I would syncro the prop to the piston position by trying different spline positions of the drive shaft to the crank. What worked the best for more rpm and speed (about 1 mph which is a lot in a race) was to get the prop blade to dive at about the 9 o'clock position (looking forward) with the piston at TDC (not many choices with the limited spline numbers but it can be done). Never played with this using 16:21 gears and 2 blade props & 2 cylinder engines, figured it wouldn't help due to the cyclical nature of blade feed to TDC position. Also indexed the plugs.
    My father always did that with my brother & my motors. Not sure it worked but one would think that at the #1 cylinder firing position with the prop just clear of the gear case you would theoretically get a better bite

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