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  1. #1
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    Aug 2016
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    Default disappointed w/ the perf of bass boat

    Hi,
    I have a (I think) a 1988 erude, 75 hp 3 cyl, w/3 ½” case (@prop) I have searched this eng top to bottom n cannot find any decal, data plate, freeze plug, or any type of id for mod#. Prop is stamped 13x10, w/13 spl. Eng mounted to a 16’ stratos 256V bass boat, (893#)
    I bought used several yr ago, not used much, bcuz have been disappointed w/ the perf.
    Real slow to plane, and top spd is only 27 mph, by gps. Now the prob. Was cleaning prop to repaint and found cracked blade. SO, started searching for repl and found some strange stuff. First ‘88 ‘75hp erude prop? don’t seem to exist in prop listings. Can list for ‘70hp n ’80.
    Is this wrong prop? Or what? I’m OPEN to most sug reposted this becz of following
    OK, I was inspecting my engine (for the forever time) I found a clamp mounted wrong n wz blocking throttle from going wot.
    Took to the lake yesterday, w/about 400# of ballast along (2 leg type), still sloooow to plane, top spd improved to 31-32mph, using gps, top rpm of 5200-5300.
    Still open to sug

  2. #2
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    Nov 2011
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    tennessee
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    Default Re: disappointed w/ the perf of bass boat

    How about a picture of motor??Does it have trim??
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  3. #3
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    Aug 2016
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    calera, Al
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    21

    Default Re: disappointed w/ the perf of bass boat

    Tried pic 3 times n no luck. yes ptt n it works fine. that's how i got to32mph

  4. #4
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    Default Re: disappointed w/ the perf of bass boat

    Tryn pics again

  5. #5
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    Default Re: disappointed w/ the perf of bass boat

    Prop is stamped 13x10,
    I suspect that is a 19pitch as a 10pitch would be around 8500rpms....
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  6. #6
    Join Date
    Nov 2005
    Location
    Mt. Zion, Illinois,
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    Default Re: disappointed w/ the perf of bass boat

    I did some searching and 75HP is max for that boat, so this will have to work somehow. Bass boats are notorious for poor holeshot performance because of all the weight in the stern. The only way to overcome this is more power and/or more prop blades. The other gotcha is these 3 cylinder motors have low torque and HP at low RPM. They'll run for ever, but they aren't power houses.

    If Faztbullet is right, you might be slightly over-propped with a 19P. Your engine WOT RPM (now that you solved the clamp problem) indicates you're down about 200-300 RPM from max rated WOT RPM. If you go to a 13-1/4 X 17P prop you should regain those lost RPM. Usually each change in pitch effects the engine by 150RPM.

    One way to help holeshot is to drill ventilation holes in the prop. The idea is the holes let exhaust bubbles flow over the prop blades at low speed creating cavitation. The cavitation lets the prop 'slip' in the water and engine RPM increases faster. Higher RPM equals more power and you get more thrust faster. Eventually as you speed up the exhaust gets sucked out the back of the prop and stops the cavitation. You can drill these holes yourself and test the prop to see if you get an improvement. The pic below has instructions on how to do this:

    If you go to a 17P prop and drill the vent holes you should see improved holeshot and maybe a little better top end speed. If a 17P puts you over the max RPM you could stick with that pitch but get a cupped prop. Cupping gives the prop a little more bite and thrust so it does pull down WOT RPM a bit.

    Click image for larger version. 

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    Last edited by kevinj; 09-19-2016 at 04:11 PM.

  7. #7
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    Default Re: disappointed w/ the perf of bass boat

    Thanks,
    I know (some) about the way prop pitch works. This one is stamped 13x10, n have measured dia @ 13", so I guess the pitch is 10", so if I repitch to 19", wont't that kill top end?

  8. #8
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    Nov 2005
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    Mt. Zion, Illinois,
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    Default Re: disappointed w/ the perf of bass boat

    Yes, the first number is the diameter and the second is the pitch. 13"D is a very common size aluminum prop for the 3 cylinder engines.

    Basically pitch is a measure of the angle of the blades to show how far forward the prop goes with each rotation. The more perpendicular the blades are to the prop shaft (lower pitch), the less bite the prop has and thus the less distance it travels forward with each revolution. So, your 10P prop is traveling 10" forward for each rev versus 19" for a 19P prop. It takes more power and torque to get that longer travel in the 19P prop.

    I am really baffled by the 10 pitch. That 75HP should easily turn a 17P prop all day long. If you take a look at this prop-speed calculator, you'll find it doesn't seem right that yours is a 10P.

    http://propellerhub.com/boat-speed-calculator.html

    I believe your lower unit uses a 2.42:1 gear set (someone please correct me if I'm wrong). In the calculator if you entire 5300RPM, 19P, 2.42 gears, and 12% slip (pretty average slip #) it estimates your boat speed to be 34.7MPH. Now, if you change the prop to 10P that estimate decreases to 18.25MPH. I know you're seeing a 10 stamped for the pitch, but that just doesn't sound correct given the speed and RPM info you've provided. Also, I've used calculators like this for years and the numbers are fairly accurate.

    Do yourself a favor and try to find a cheap 17P prop (that has a good hub and blades) and put that on the boat. For example, this Ebay listing is for a 11 3/4 X 17P stainless prop.
    http://www.ebay.com/itm/OMC-Johnson-...dXyY~f&vxp=mtr
    I think it should fit. Basically all you need is a prop for a 13-spline shaft and 3 3/8" gear case. I believe the 40HP/50HP engines used the same size gear case as your 75HP. Or, maybe your local boat shop would have one you can borrow for testing purposes?

    Here's where I'm going with this. If you put on a CONFIRMED 17P prop and your RPM @ WOT increases to 5500 - 5600 then you can safely say your current prop was in fact a 19P. Also, when you trial the 17P you should see a noticeable improvement in holeshot.....assuming your current prop is a 19P. Now, if the 17P causes your RPM takes a massive drop by 1,000 RPM or more and performance is an absolute dog, then you can conclude your current prop is indeed a 10P. If the 17P turns your performance to absolute trash, then you have MUCH BIGGER FISH TO FRY. That means for certain you have serious issues with your engine, you are WAYYY down on power and you need to start digging in to find those answers. OR........it could mean your engine is not set properly on the transom (too low) or........the foam in your hull is completely water logged and you're trying to push hundreds of extra pounds with that engine.

    In reality, low to mid 30's for speed is about the max you're going to see. I had a '78 Johnson 70HP on a 15' tri-hull boat many years ago. About 30MPH was the max speed I ever saw out of that combination. If I planned to just cruise around I used a 17P prop. However, if I knew I was going to pull skiers or tubes on a given day I would switch down to a 15P prop. The lower pitch would give a little more thrust from the hole and make it easier to pop up skiers. The trick was I had to watch my WOT RPM because the 15P would allow me to over-rev the engine.

    Please take my advice and try a prop that you know for certain is a 17P. Once you've done that you can rule out many unknowns.

    KJ

  9. #9
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    Default Re: disappointed w/ the perf of bass boat

    If that was a 10p prop the RPM on tach would be 8000+!!!! You most likely have a 19p due to your info posting results. That rig will max out about 40-44mph with 1 person
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  10. #10
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    Aug 2016
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    calera, Al
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    Default Re: disappointed w/ the perf of bass boat

    Tryn pic againClick image for larger version. 

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  11. #11
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    Default Re: disappointed w/ the perf of bass boat

    More picClick image for larger version. 

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  12. #12
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    Nov 2005
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    Mt. Zion, Illinois,
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    Default Re: disappointed w/ the perf of bass boat

    The motor setup looks fine. Your cavitation plate is just about level to slightly above the bottom of the hull so you're not getting excess drag from the motor itself.

    Can you take a picture of the stamped #'s on the prop? The part# and/or diameter X Pitch should be stamped either on the outside of the hub by one of the blades, or it will be on the back of the hub where the prop nut and washer tighten down. You'll have to remove the prop nut to get to that but it should help clear up any confusion.

    The pic below is an example of what you should see behind the prop nut if you have an OMC prop. The hub housing should have the OMC part# and pitch molded in. I think aftermarket props also have numbers molded/stamped here as well but I don't know if they put the D x P like OMC does.

    Do you have access to get a 17P prop for testing like I suggested? At bare minimum, testing a prop with a known pitch can answer a bunch of questions.

    Click image for larger version. 

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    Last edited by kevinj; 09-21-2016 at 01:16 PM.

  13. #13
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    Default Re: disappointed w/ the perf of bass boat

    One other thing, in your pictures I don't see any ventilation holes on your prop. If you follow the guide I posted earlier those holes should help you significantly when taking off from a dead stop.

    KJ

  14. #14
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    Default Re: disappointed w/ the perf of bass boat

    PROP PIC.
    No. haven't done anything yet. i'm 70+ yr old. don't get to get around as much as i would like.
    BTW, a big THANKS!!!, to all that r helping me.Click image for larger version. 

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  15. #15
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    Default Re: disappointed w/ the perf of bass boat

    OK, here is a blast from the past.
    Old adjustable pitch prop, set at 10, on top of my prop. Click image for larger version. 

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  16. #16
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    Default Re: disappointed w/ the perf of bass boat

    What as mess of cobbed together parts.....The lower unit is pre 78 as it has the straight skag, the lower unit is pre 76 as it a reverse shifting unit thus the bellcrank, prop is a 19..the 9 is misscast and looks like a 0, midsection and motor pre 1985 as no fittings/bracket for VRO, has a butterfly choke instead of enrichner, cowl has been repainted but emblem dates it as a 1982.
    Its the 49ci motor so high 30's(34-37mph) will be about with 1 person and normal load.
    Last edited by faztbullet; 09-21-2016 at 10:04 PM.
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  17. #17
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    Nov 2005
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    Mt. Zion, Illinois,
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    Default Re: disappointed w/ the perf of bass boat

    Quote Originally Posted by faztbullet View Post
    What as mess of cobbed together parts.....The lower unit is pre 78 as it has the straight skag, the lower unit is pre 76 as it a reverse shifting unit thus the bellcrank, prop is a 19..the 9 is misscast and looks like a 0, midsection and motor pre 1985 as no fittings/bracket for VRO, has a butterfly choke instead of enrichner, cowl has been repainted but emblem dates it as a 1982.
    Its the 49ci motor so high 30's(34-37mph) will be about with 1 person and normal load.
    Nice catch on those details, I sure wouldn't have seen all of those variances. I agree on the prop pitch, those 9's often didn't cast properly and would sometimes look like a 0. It's definitely a 13X19 prop.

  18. #18
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    Default Re: disappointed w/ the perf of bass boat

    Quote Originally Posted by j kyzer View Post
    PROP PIC.
    No. haven't done anything yet. i'm 70+ yr old. don't get to get around as much as i would like.
    BTW, a big THANKS!!!, to all that r helping me.Click image for larger version. 

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    No problem. Given FaztBullet's reply it looks like your motor has had some work over the years. Now that we've confirmed you have a 19P prop I'd say your engine is performing just fine if you are getting 5300RPM @ WOT.

    For now, let's not spend any extra money but try to improve the holeshot performance. Follow the guide I posted above and drill the ventilation holes in your current prop. There are many new props that come pre-drilled with these holes so you won't be damaging anything by doing this. When you drill the holes you might start with a smaller bit, maybe 1/16" or 3/32" then gradually step up until you get to 3/16". I really do think you'll see a nice jump in holeshot performance once you do this.

    Top speed is certainly not where you want at 27MPH. Aside from dropping down to a 17P prop I'm not sure there is much else that can be done to improve your top speed. Is 27MPH at max trim? Do you have a trim gauge? Maybe you could play around with the trim to get more of the hull out of the water and reduce drag? The only other explanation as I mentioned before is maybe the hull foam is water logged and you're just pushing a bunch of extra weight which is reducing top speed.

    Going slow is no fun, especially on long runs. But.....in the end this is a fishing boat, not a speed boat. I know many of us bass fisherman get wrapped up in boat performance going 70+ MPH, ripping to a fishing spot. The issue at hand is to ask yourself if the motor is reliable, does the boat get you to the fishing spot, and is the rig setup for your style of fishing? If the answer to these questions is yes, try to step back and accept the boat for what it is.

    My previous bass boat was a 16' aluminum Sea Nymph rig with an Evinrude 40HP. About 37MPH was max and it was a bummer to watch other boats pass me during tournaments. But, the boat was affordable, the motor was reliable, and it got us to our spots. The only gotcha was it was too small for our tournaments. In Illinois, bass fishing is a high school varsity sport and I was using my boat to take my son and other kids out for tournaments. Between all the rods, lures, tackle boxes and 3 people in the boat it got cramped and sometimes dangerous. That was the only reason I got rid of the aluminum and jumped up to my Ranger. If it were just me going out fishing for fun, I'd still have the Sea Nymph.

    KJ

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