upgraded outboard motor predictions...realistic?

Discussion in 'Boating' started by StuBone278, Apr 7, 2008.

  1. StuBone278

    StuBone278 New Member

    Messages:
    625
    State:
    south central Louisiana
    Well looking into I'm getting the new Tohatsu 20hp 4-stroke within the week for my WeldCraft flatbottom 1432 jonboat. It's all-welded and weighs around 210 pounds empty, and at the moment I have been running a Briggs/Stratton 5hp. By myself I can get it up to around 13mph with light gear, but with more than 2 light people on it it can't even plane.

    1). Will it still be realistic to plane with 3 or 4 (~145lb.) guys?

    I then found this plane speed calculator. I entered all the weight and hp and speed to get a constant of around 135. According to the calculator, I should be able to get around 25-27mph with the 20hp while by myself. Anyone ever test this calculator to be accurate? What are yall's jonboat constants at?

    Thanks!:big_smile:
     
  2. Megalodon

    Megalodon New Member

    Messages:
    7
    State:
    georgia
    I have the same size boat. I just upgraded from a 5 hp gamefisher to a 20 hp honda. My max speed with just me (205 lbs.) and light gear in the boat is 26.4 mph, so your estimates appear to be right on. I've been out a couple of times fully loaded down with gear and one other person (240 lbs.) and the boat got on plane just fine, although a bit slower. It sounds like you may go faster considering our weight differences.
     

  3. chris dornbusch

    chris dornbusch New Member

    Messages:
    79
    State:
    iowa
    Where did you find the calculatoe at, on the web or did you buy something? I Thanx
     
  4. cantstopgrandma

    cantstopgrandma New Member

    Messages:
    955
    State:
    MD
    I'd say your numbers are pretty close. I've got a 1448 flatbottom jon that weighs 260# empty, 100# motor (25hp), i'm about 250 and fish with someone that is 200. I figure about 50# of gear give or take 10 or 20#. My boat will go about 26 or 27mph by my gps wide open. I cruise about half throttle 22mph. With just me in the boat it'll do about 28 or 29 mph wide open. Your boat should definately plane with 3 people, 4 might be pushing it, but i'd say it probably will.
     
  5. chambers bd

    chambers bd New Member

    Messages:
    1,134
    State:
    Sautee,Geo
    Hi Folks,
    Some thing that may help is a sting ray type fin on the bottom of the motor to channel and direct the pushed water, It helps on every boat I have had!
     
  6. seaark ryan

    seaark ryan New Member

    Messages:
    199
    State:
    Kansas
    I have a friend that has a 1436 lowe with a 15 hp 4 stroke nissan and it will run 20 on gps with 2 people. They load it down with 4 guys (way overload) small end guy 155 top end 210 and it will still plain out. I have a 1448 lowe with an old 18 hp johnson that runs good and the 15 blows mine away! I am planning to buy a 20hp Tohatsu this month with my tax return. I know this is a late post but if you have aready got yours how do you like it and how fast is it running your boat?
     
  7. seaark ryan

    seaark ryan New Member

    Messages:
    199
    State:
    Kansas
    Just thought I would add a pic for you all to look at!
     

    Attached Files:

  8. Dsage

    Dsage Active Member

    Messages:
    2,137
    State:
    Topeka, Kansas
    Ryan I think that the picture would be better if GPS coordinates were given. :big_smile:
     
  9. AwShucks

    AwShucks New Member

    Messages:
    4,532
    State:
    Guthrie, Oklaho
    Ryan, your just lucky superman was in the boat with you. A cat that big could probably whip a man in 10 foot of water. LOL
     
  10. StuBone278

    StuBone278 New Member

    Messages:
    625
    State:
    south central Louisiana
    YES! The predictions were RIGHT ON! 27mph by GPS by myself and it was not even topped-out, it would over-rev after that. Easily 22-25 with 3 (140-150lbs) people in the boat. The Tohatsu 20 is a kicka$$ motor, with lots of low-end torque. BIG step-up from the 5-horse. Almost done breaking it in, can only run WOT for a few seconds at a time, and it's more than I care to. I can cruise with a few people around 18-20 at half throttle. The acceleration is abonoxious.

    I'ma get some pictures of my boat next time I'm about to go fishing....it's a really nice looking rig now with a new aluminum/wood deck!:roll_eyes:
     
  11. seaark ryan

    seaark ryan New Member

    Messages:
    199
    State:
    Kansas
    Are you kidding I wasn't in that little ass boat with all of them guys. I was in my big boat and the camera. I will say this, that little boat has seen a lot of big flats though!!!!