MPH question?

Discussion in 'Bubba's Outboards' started by tbull, Dec 7, 2008.

  1. tbull

    tbull New Member

    Messages:
    3,318
    State:
    SW Ohio
    I am running a 94 Evinrude 112hp motor on a 19ft Aluminum deep V. Max speed is usually about 40mph, does that sound right? The 70hp Johnson I took of would run the boat around 30mph, just seems I would get a little more from the 112. If it sounds right then so be it, just curious...thanks all.:wink:
     
  2. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    Thats probally about right.
    One would think if you went from a 50 to a 100 you would double your speed along with the horsepower. It dont work that way.

    Having a library of boat plans most will list engines and speeds.
    Many times you can go from a 100 to 225 and only gain 5- 10 MPH and sometimes less depending on the hull.
     

  3. tswebb71

    tswebb71 Member

    Messages:
    405
    State:
    So. IL
    I agree with Mark. That sounds about right. the horsepower to speed ratio is definitely not 1:1 or even close. It seems like after you reach 40-50 MPH, it becomes extremely difficult to gain much speed.
     
  4. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    Hull speed.
    Every hull has it's optimum speed. Once you reach it it takes more and more to achieve less and less.

    Look at displacement hulls. Once hull speed is reached with say a 15 horse diesel jack shaft configuration you can rip that out and put a 200 horse in it and it wont run a bit faster.
    You'll be inefficient as hell though
     
  5. CatfishAngler25

    CatfishAngler25 New Member

    Messages:
    70
    State:
    Prestonsburg,Kentucky
    Yeah It has alot to do with the hullvs.hp
     
  6. metalman

    metalman Well-Known Member

    Messages:
    3,463
    State:
    IN
    Name:
    Winston
    Travis,
    If it helps, I have a 19ft Alumacraft deep vee with a 115 Yamaha on it. It tops out at 39mph with 2 people, 30 galls of gas and all the gear...W
     
  7. tbull

    tbull New Member

    Messages:
    3,318
    State:
    SW Ohio
    Great thanks guys, sounded right to me to, but you never know. I realize hull and weight plays a big part in it as well. Thanks for all the advice..:wink:
     
  8. StuBone278

    StuBone278 New Member

    Messages:
    625
    State:
    south central Louisiana
    Also realize once you hit around 50 mph water seems to be about as hard as cement! Something to think about, having to push that much water!:roll_eyes:

    Something else I just thought about, is that why Jet skis can go so fast? I know they are basically a motor with handlebars, but there's also no big lower unit to have to cut through the water...
     
  9. Steven Armstrong

    Steven Armstrong New Member

    Messages:
    405
    State:
    Sallisaw,Oklahoma
    how do size up the right motor for the type of boat? i know on our boat the name plate says 90hp, the fellow we bought the boat from put a 70hp when he bought the boat new, to me it seems that the 90hp would have to run at less rpm`s and with more power, but some i have talked to says thats not all ways the case
     
  10. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    There is an optimum setup for a boat.
    I'm not looking at speed. I'm looking at performance.
    These aren't cars. These things have to float, handle, pick up and carry the load.

    The speed hunters throw hundreds of bucks sometimes thousands in search of 2 or 3 MPH and for what?
    To beat me by 3 miles over an hour long run?

    Here is a prime example of spending thouands in search of a few more MPH and this is typical of like hulls.
    Center console 23 footer offshore boat. Deep V with a total weight of boat and gear at 4000 pounds.
    300 HP will push it 45 MPH max.
    225 HP will push it to 39 MPH.
    The gain doesnt justify the expense of buying or operating 300 horses over the 225. We're talking a paltry 6 MPH difference.

    My opinion based on what most designers worth a flip freely will tell you that in the name of safety the "utility" type hulls have a safe speed limit. Most fall within the 25-40 MPH range. Alot of these boats are hard chined boats and the center of gravity isn't real fabulous. They are prone to skipping, chine walking and porpoising. In other words its quite easy to get into more then you can get out of fast enough. Throw in the captains experience or lack thereof and you have a handful at best or a disaster in the making.

    It's part of the compromise of choosing a boat. You have to give up to get.
    You want to go fast, pick the hull for going fast. Dont take a barge and keep throwing motor at it.
    It's akin to putting a Corvette engine in a Pacer. Sure it might go fast but you lack an important componet of going fast. The handling of the Corvette.
     
  11. Fishmaster1203

    Fishmaster1203 New Member

    Messages:
    3,603
    State:
    PA
    Faster is Better! :big_smile:
     
  12. cantstopgrandma

    cantstopgrandma New Member

    Messages:
    955
    State:
    MD

    You haven't fished out of a flatbottom boat on a windy day lately have you? :big_smile:
     
  13. Steven Armstrong

    Steven Armstrong New Member

    Messages:
    405
    State:
    Sallisaw,Oklahoma
    better have your teeth glued in good! we fish out of a 19 ft. flat bottom, it can get rough!
     
  14. Grimpuppy

    Grimpuppy New Member

    Messages:
    3,556
    State:
    Concordia, KS
    My 19' Mod "V" with a 115 motor tops out at about 37 MPH fully loaded with gear and 3 people and smooth water. 40 MPH with just me and a light load.
     
  15. catfishcrazy256

    catfishcrazy256 New Member

    Messages:
    2,648
    State:
    Indiana
    This is very true!!!
     
  16. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    A car is rolling on wheels and more horsepower will increase speed along with proper gearing.
    A boat is a different animal. You have the friction of a hull on water and vacuum.

    If you look at some of the racing boats particularly the drag boats, the bottom of the hulls aren't slick as glass. They rough them up to create air pockets and bubbles which equates to less friction and breaks the vacuum. This has become more popular among the bass boating crowd in the last several years too. Folks is doing some mean things to those pads.:smile2:
     
  17. Mark J

    Mark J New Member

    Messages:
    9,407
    State:
    Four Oaks, NC
    The right idea is to think in terms of power instead of speed.
    There is that compromise again.
    You got bait wells toting 300 pounds of water in them and 100 gallon livewells 500 pounds of water or more. You need adequate power to get the boat on plane and keep it there without having to run wide open. More motor makes more sense in this respect. In regards to speed it doesnt.

    The compromise is in the prop. You have blade configurations to produce more speed but they lack in that "pulling" power and your plane speed will be higher.
    Ever seen those ski shows where the Ski Natiques are pulling 10 skiers? It's a compromise. You can make that boat run 70 MPH with the right prop especially since its running a 351 under the hood or a modified 400 but you wont be pulling up 10 skiers at the same time with the 70 MPH prop. It dont have enough blade.

    The big thing alot of people over look is plane speed. You dont want to go so far that you have to be running 25 MPH to saty on plane. Believe me it happens particularly if you are under powered or have a poor setup. Hull has alot to do with it too. Those speedy hulls are bad for higher plane speeds leaving your cruise speed way up there.
    Flat bottom boats excell in this area as they are on plane sitting still.

    Nothing like a finely tuned setup in a boat but unfortunately it's highly unlikely you'll drag it home with a finely tuned setup. It's something that takes some time, effort, and experimentation which usually costs money.

    The home boat builders go through this all the time. Building it is one thing and once you have the time effort and money into building it you want the most you can get out of it. Most of us spend alot of time tinkering with the setup in a myriad of ways looking for that perfect fit. Every boat is different and the weight distribution is different from boat to boat. A big key on any boat is is knowing where the CG should be whether it 60% or 55% of the length starting from the stern.
    If you are building off plans you know what it is. If you are buying off the lot, good luck. You get a dealer rig and setup and they probally dont know and will probally look at you like you are crazy if you ask.

    Dont sound like a big deal? Go to putting 100 gallon livewells and 30 gallon baitwells in a boat wherever you can fit them. Sure the boat may handle it but how well is it handling it? You get off your CG and it can not only effect performance but safety. If your CG is out of wack you may wind up with a boat that wants to dig bow first into waves instead of going over them. Not too big of a deal until you get caught out in a bad situation.
    Out of CG may cause a dangerous broaching situation which you wont know until you broach and your toes wind up tickling your tonsils provided you dont go under in about 2 seconds flat. Broaching will only dirty your drawers if you are lucky.

    If you go stacking all this weight too far forward you can alter the CG with a motor bracket like you see on the offshore outboard boats. Hang the weight of the motor further off the stern. Works like a fulcrum. Only a couple problems. Motor brackets are expensive as all get out. Several thousand dollars and they really aren't as effective on a boat under 23'.

    Yea, I know its a little over the top and kind of technical but such things should be considered especially if you want the most out of what you bought while keeping it safe. Just because it fits dont mean its a good fit.
    Safety should be a major concern. Fishing a slow river with not much traffic you can get away with more. Fishing large bodies of water or rivers with alot of traffic you need to be really cognizant of your CG. Things can go bad real quick.
     
  18. roadkill636

    roadkill636 New Member

    Messages:
    551
    State:
    warrenton misso
    my 2472 seaark tops out at 53 mph "GPS" with a 200hp 2 stroke
    22 pitch prop 6300 rpms surfacing the prop with a jackplate
    but this was with 28% prop slip....VERY inefishent,,,but makes a good look'n roostertail

    I'v noticed that a lot of people "estamate" there speed....Its amazing how heavy a gps unit will slow down a boat !!!!
     
  19. larry d. grady

    larry d. grady Member

    Messages:
    331
    State:
    north caro
    hi travis ,to be sure ,you need a tacometer,if you are running wide open you should not exceed 5200 rpm's,if you are not turning 5200rpm's then you don't have the right prop on the motor for the size of your boat,or your motor isn't performing to it's potential
     
  20. TrophyHunt

    TrophyHunt New Member

    Messages:
    25
    State:
    Georgia
    I agree with the prop. I think adding more pitch will increase your top end or is it the other way around. I gone from a number 13 to a number 17 on my 40 and you could tell a big difference. But you have to be careful the larger the prop size the more stress you put on you lower unit. And trying to gun it from low speeds can result in replacing your lower unit. It will also cause you to take more time to get on plain.