Johnson 48spl ?

[longshot]

I have a few questions for you guys.<br /><br />I have a 1996 Johnson 48spl. What is max WOT RPM. It has no tack on it now, but am plannin on getting a tiny tach.<br /><br />I am also not real pleased with top speed with the rig. It is on a 1650 Xpress welded Jon boat. With me and a buddy it runs almost 33mph.<br />I have a 12 1/4 X 15 prop on it. What follows are a few problems that it has.<br /><br />I am also having a problem with the boat prop cavitating? I HAVE to run the boat with the motor tilted all the way down(gas assist). While the boat is running it is level and has too much drag I think. The prop I have is also cupped.<br /><br />thanks<br />longshot

 

[rickdb1boat]

Re: Johnson 48spl ?

longshot <br />I'd say your WOT(Upper end) should be between 5500-6000 RPM's. According to the prop chart, you are propped close with the 12 1/4 X 15 for your boat size. Of course, without the Tach. it's impossible to tell for sure. Is the Cavitation plate even with the bottom of the hull? I wouldn't expect much more than 35-37 MPH out of your set-up, even if everything is right on. What kind of prop are you running(Brand, Material, Ect.) How does it do with only you aboard?

 

[longshot]

Re: Johnson 48spl ?

I am running a aluminium OMC prop. My motor is in the lowest mounting hole on the transom. I have never GPS it with just me.<br /><br />longshot

 

[rickdb1boat]

Re: Johnson 48spl ?

But is the Cavitation plate even with the bottom of the hull?

 

[longshot]

Re: Johnson 48spl ?

Yes, it is slightly below even.<br /><br />longshot

 

[FlyBoyMark]

Re: Johnson 48spl ?

Your rig weighs about 675 lbs with nuttn' in it, + motor 200 or more lbs, + battery 50 to 120 lbs, + fuel@ 6.5 lbs per gallon, + you(are you a "BOB"?), + any other junk you have accumulated over time...Your speed is rite in the ball park. My Micro-Mini 13'10" V-Hull bass boat with a 2000 Merc 3 cylinder 40HP weighs in at 650 lbs fully rigged + me and I get only 38 MPH @ five grand....Cupped props are generally for speeds over 45 MPH. To get into that realm, your gonna need a 70 HP or better for your particular rig(whats the boat rated for?) and the prop literally has to run with part of the top of the prop out of the water to be efficient. If you feel the prop is cavitating, I would look at the condition of the prop and if it has a rubber hub, check to see if it has been spun or slipping

 

[longshot]

Re: Johnson 48spl ?

bout 275# worth.......if that is a "BOB" LOL<br /><br />boat & .125 al floor @450#<br />motor 185#<br />gas 40#<br />batt. 100#<br />me and buddy (really "BOB") 600# <br />trollin mtr 30#<br />asst. fishin crap 30#<br /><br />total @1400#<br /><br />guess i am doin ok then for speed<br /><br />the boat is a flat jon boat that is rated for up to a 70 horse<br /><br />longshot

 

[FlyBoyMark]

Re: Johnson 48spl ?

Not bad at all for that weight your push'n 'round. Plus itsa 16' boat. 70 hp would get you over 45 but to 50.....mmmmmm I dunno. Bit a eekn' and tweekn' it might do it.