15hp mercury help needed bad

Discussion in 'Outboards' started by racing fan, Feb 12, 2011.

  1. jerr0
    Joined: Oct 2012
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: 31566

    jerr0 New Member

    when motor was to low the 15hp never realy hit top rpm I to was looking for a way to increase hp thats is what brought me here to this forum. the river that I fish is now to low for a prop motor ,I have a 25/20 Jet on the V bottom smoker craft.All the rules about jet says this not the boat for jet motor, they were right untill i used the same 1 1/2 block under that motor. the motor is only 1 inch below bottom of boat. big difference.
     
  2. tunnels

    tunnels Previous Member

    Its good to have some extra horses !!

    Set up is very important in any boat specially in small boats . just small thing can make a noticable differance . 1.5 below the bottom needs to come up to level with not below . means the leg is causing more drag in the water that it should . tilt from the pin sometimes just a half a hole is all thats required to make a differance as well one setting is to high and the next down is to low I uses a short length of garden hose and slid it over the pin on the small boat we were using .
    14 feet you should be able to mount a 40 without to much problem . Just any extra weight that goes in the boat needs to be in the middle of forward of .
    While you sitting down i have a 14 foot semi cabin boat with a 115hp vee 4 yamaha ! over powered yes but its a lot of fun ,leaps out of the water like a jet ski, its an old boat and i made a complete new transom because it was wet and heavy and the only piece of wood in the whole boat . Had a very tired 70 hp when i first got the boat ! was ok but always working hard it was time for a big change !!
    The advantage of having lots a grunt is its there if you need it ,but for cruising i dont even use 1/2 throttle . It runs on the smell of a oily rag and i love it !! :):p:D:p
     
  3. jerr0
    Joined: Oct 2012
    Posts: 4
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: 31566

    jerr0 New Member

    I will be messing with height adjustment, thanks for info, I got to do this,you know. wonder how "racing fan" is doing with his motor upgrade? to me setup would be first then more power ,that would be best of both worlds
     
  4. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 498, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    In small craft, trim can mean just as much, if not more than ventilation plate installed height. Scooting your butt forward a few inches can mean a few hundred extra RPM, literally, especially with tiller steered craft.
     
  5. tunnels

    tunnels Previous Member

    Yip i used a piece of White plastic water pipe about 1 metre long that was a snug fit over the tiller handle so could twist the throttle and sit forward . Its a really good learning exsperiance trying differant things in a small boat the same principles apply to bigger boats as well !!:D
     

  6. PAR
    Joined: Nov 2003
    Posts: 19,126
    Likes: 498, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Us in the designing world call this the Cb calculation (Center of butt) . . .
     
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