More speed please

Discussion in 'Bubba's Outboards' started by etexun, Jul 9, 2008.

  1. etexun

    etexun New Member

    Messages:
    375
    State:
    Texas (Nea
    Ok, I am like most guys. I want more speed out of my motor. I posted a question a little while back about it blowing the head gasket and got some good replys. And after taking the advice and pretty much wearing my arm down to a numb nub by working the head piece around and around on several different pieces of emory cloth the true it up. I am ready to move on to the next problem. More speed.
    I just can't accept that it wont get up and go any better without trying other things to coax it along a little faster. The more I look into it, the more things I find that might be holding it back.
    I am running a 1976 Johnson 35hp. I think is pushing about 5500-6000 rpm's. I don't have a manual so does anyone know if that is right?
    I did some calculations using the prop on it and, I'm no mathmatician, but I think I am only working at half that, around 2600rpm. If I am close on that then that would explain why it has no get up and go.
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    1. I think I might have the wrong prop on it. I got it with a 10.5x13 prop. It is on it now. But I am thinking of dropping it to a 10.5x11. (will that improve take off and top end? If so how much? )
    2. My neighbor says I need one of those fins on the cavitation plate ( how much would that help me?)
    3. Another thing I foud out was my motor might be setting down a little too far. From a level line to the bottom of my boat out to the cavitation plate the motor is a little more than an inch lower than the bottom. The motor is about 8 inches out from the transom at this point. (I will have to have the transom built up a little to accomplish this. But I will have it done if it will help.)
    4. I found that the motor was setting at a canted inward angle to the bottom of the boat and I corrected that. I think it might have been causing the boat to try and submarine down at the bow.

    Right now I can't lighten the boat any but later I am going to take all the flooring I just put in it out. And replace it with an Aluminum one.

    Thanks for any advice and help.
    If after doing all this, I can get it up around 30mph I would be happy.
     
  2. Cuda

    Cuda Active Member

    Messages:
    553
    State:
    Iowa
    Name:
    Mike
    What size boat are you pushing? And the motor should be tipped out at the bottom. With it that way you can get on plain faster and go faster. And the lighter the boat the faster it will go. Try keeping the load in the boat to the back. A whale tail will slow you down I tried one on my 25hp. A v bottom pushes harder than a flat. I hope this helps.
     

  3. Team Hold EM Hook

    Team Hold EM Hook New Member

    Messages:
    272
    State:
    al
    To expand on the whail tail, it will stabilize your boat. However that plastic is a lot less britller than the cast aluminium on your engine foot. If you hit something w/ the fin hard the fin will break whatever it is bolted to. Been there done that!
     
  4. etexun

    etexun New Member

    Messages:
    375
    State:
    Texas (Nea
    I posted pics of my boat under the BOAT MODIFICATION heading. It is listed as "Flatbottom Project". It is 16ft long and nealy 6ft wide across the top. It is not a lightweight boat. This aluminum boat is heavy.
    More of the weight will be at the back because of the gas tank, motor and me.
    Even working on all these detail I may not ever get it up to where I want. But I have to try. Every little bit will help.
    If I can't get it up where I want it I guess I will start looking for a little larger motor and just pass this one on to my son for a 14 flatbottom project for him.
     
  5. Bubbakat

    Bubbakat New Member

    Messages:
    4,532
    State:
    McMinnvill
    Before you change anything on that motor my suggestion to you would be invest in a good accurate tach. Stop guessing at those RPM's because if its turning 5500 to 6000 you are going to be running it one day and its going to make a loud distinctive knock and it will power down and you will be in the process of finding another motor. When we get some good tach readings on this situation then will I offer any suggestion because without it you are only guessing and will do more damage then can be repaired.
     
  6. chambers bd

    chambers bd New Member

    Messages:
    1,134
    State:
    Sautee,Geo

    Hey Guy,
    You really need to consult with bubakat, you can go by a marina and im sure they can hook your motor up to a tach to give you a rpm on wot.

    A hydro foil will help your boat in many ways, I choose to get a xpIII by stingray! Its mounted by one bolt and does not void a warranty on the motor. It gives better control,speed,fuel economy, and will help you get on plane much faster.

    You can put a Jack plate on your boat and adjust the height of your motor.

    Your motor must be able to pull the load, so once you get a picture on the RPM verus WOT you can adjust the propeller pitch. By adding to the pitch you can add to your top end. It will hurt your hole shot. Most motors in the 35 hp range will come from the factory with the correct pitch propeller.

    The internet has many calculators for speed once you get your numbers down. Most have Five variables.

    The flooring does add weight.

    You can adjust your speed some it will cost when start changing the propeller.

    I hope, Ive gave you some usefull information.

    Brian
     
  7. etexun

    etexun New Member

    Messages:
    375
    State:
    Texas (Nea
    Guys,
    Thank you for any and all suggestions. I had not thought of looking into the Tachometer, but it is a really good place to start. I will see where I can scatch one up and see what my motor is putting out, before I make any changes.
     
  8. BailBonds

    BailBonds New Member

    Messages:
    282
    State:
    Indiana
    As far as props, I've found this calculator to be helpful. I bought a pontoon that had a prop way too big and it would never get close to the RPM called for at WOT. Most don't realize how important a properly sized prop is.

    http://boatmartusa.com/marinemall/propPage.php
     
  9. seokfisherman

    seokfisherman Member

    Messages:
    442
    State:
    Oklahoma
    I mounted a 2004 Mercury four-stroke 15 horse onto my 14 foot V-bottom. It didn't matter which way I set the motor it tried to porpoise or did not plane right. I added a SE Sport brand whale tail to the back of my motor and was finally able to get the boat to ride right. Of course with my small boat weight and where the weight is placed in my boat drastically affects the speed and the ride.