Prop Confusion ????

[dh703]

I have a bow rider 17' boncraft 1978, it is like a Monarck and it is a trihull it has an Alum. prop that is damaged, the engine is a Johnson 115 HP V4 not sure of the correct rpm due to I just bought the boat and don't have any books nor can find any on the boat.

I use the boat to fish and tow kids on towables, bit the prop is damaged due to sand bars, when I looked up the part number for that engine the confusion started, 3 blade vs 4 blade diam. and pitch??? can some please explain the differences and suggest the correct prop for use.

Water type is fresh, brackash, and salt water use. I am a new boater and your help would be greatly appreciated.

 

[hwsiii]

Re: Prop Confusion ????

DH, take the prop off and give us everything that is written on the prop, look on the sides and inside the bak and front of the prop.


H

 

[dh703]

Re: Prop Confusion ????

let me go do that now and I will let you know, thanks be back soon

 

[dh703]

Re: Prop Confusion ????

It is a Michigan wheel 13X19 number 011004.

 

[hwsiii]

Re: Prop Confusion ????

I will be here.


H

 

[steelespike]

Re: Prop Confusion ????

H,He posted at the same time as you just above yours.
Michigan, 13 X 19 number 011004.

 

[hwsiii]

Re: Prop Confusion ????

LOL Spike, I didn't see it.


H

 

[Dhadley]

Re: Prop Confusion ????

We'll assume the motor is a 1978. If so, you'll be looking for 5700-5800 rpm with an averge load. Most likely once you get your optimum prop for cruising you may find it easier to pull the water toys to drop down a couple inches in pitch. You might make do with a good 4 blade prop especially if you can get the set up close to 5800.

 

[dh703]

Re: Prop Confusion ????

So should I drop down in Diam. as well from a 13 to a 12, and you mean fom a 19 pitch to a 17 pitch which would be a 12X17??

 

[Dhadley]

Re: Prop Confusion ????

Diameter depends more on prop type / style than anything. Once we know what the top rpm and speed is on the wheel you have we can more accurately suggest something.

 

[dh703]

Re: Prop Confusion ????

Rpm gauge not working now for some reason? however top speed I had it at was 30 WOT.

 

[sbbamafan]

Re: Prop Confusion ????

WOT boat speed is irrelevent. Engine speed is all that matters for prop 'tuning' at this point. I recommend you fix your tachometer before anything else. Only then can you be sure you are turning the right RPM at WOT. Then start tweaking and changing things.

 

[Dhadley]

Re: Prop Confusion ????

Top speed is very important. Without knowing the accuratetop speed you'll not be able to calculate the percentage of slip. Once you know that then you know how efficient the rig is. Or isn't.