1979 Johnson 115HP V4 Prop question

[OFD56]

Hello I am wondering what size prop I should get for my Johnson outboard, for the best speed possible.

 

[JB]

Re: 1979 Johnson 115HP V4 Prop question

This is what the Prop Forum is for, Chris.<br /><br />Moving it there.

 

[Dave Abrahamson]

Re: 1979 Johnson 115HP V4 Prop question

Way too many unknown variables to answer that one such as weight and type of boat,motor setup, transom bracket or not, jackplate or not, WOT with the prop you have now...etc..<br />For what it's worth, I have a 97 J115 CF on a 20' CC. I run a 12 3/8 X 17 SS. WOT is about 5800 with a normal load.<br />The guys "in the know" will be along shortly with some more exprienced questions/answers for ya!<br /><br />Good Luck!<br />Dave

 

[OFD56]

Re: 1979 Johnson 115HP V4 Prop question

Ok the motor is on a 1978 18' starcraft holiday, weight is about 1100-1200 lbs, not sure what wot is, and I don't have a tach on the motor yet, the motor runs the boat at about 27 MPH gps. I think the motor and boat combo should go a little faster than that and the prop is pretty beat up so, I am planning on replacing it and just need to know what size to get. Thanks

 

[Dhadley]

Re: 1979 Johnson 115HP V4 Prop question

You should get the prop that puts you at or near 5800 with an average load. You may have to work with the set up to get "dialed in". Without knowing the rpm's you're shooting in the dark.

 

[walleyehed]

Re: 1979 Johnson 115HP V4 Prop question

I think you might want to figure about 400-500 more lbs on that boat...my 18 supersport is 2100 without me in it...

 

[OFD56]

Re: 1979 Johnson 115HP V4 Prop question

Ok so what size prop do you think I should need, I don't really have a lot of money where I can buy a whole bunch of props and try different sizes. I just think that this boat should move about 35-40 mph or so and think the prop is probably the cause. I really appreciate all the help, I am kinda new to the world of marine motors.

 

[Dhadley]

Re: 1979 Johnson 115HP V4 Prop question

In your second post you mentioned that you don't have a tach "yet". That sounds like you're planning on getting one. Let's get that first so we know where we are.<br /><br />Setting up a boat is like planning a trip. We know where we want to go, we just have to know where we are so we can figure out how to get there.

 

[OFD56]

Re: 1979 Johnson 115HP V4 Prop question

Ok hopefully I can get a tach soon I am bidding on a vintage OMC tach hopefully I win it and can get the rpms the engine is running right now.

 

[OFD56]

Re: 1979 Johnson 115HP V4 Prop question

By the way I don't think the boat weighs over 2000# the trailer is only rated for 2050#

 

[DJ]

Re: 1979 Johnson 115HP V4 Prop question

As a fact, consider that every inch of pitch is usually worth 200 RPM, up or down.

 

[Dhadley]

Re: 1979 Johnson 115HP V4 Prop question

What tach are you bidding on? It doesn't take anything special but you need to make sure it's the right one.

 

[OFD56]

Re: 1979 Johnson 115HP V4 Prop question

Well I was bidding on a vintage OMC marine tach but got outbid, so I will just have to keep looking, money is kinda tight right now, My truck payment is due