25hp prop selection

[DaveyHAZZ]

i have 25 hp johnson on my 1992 tracker. its 16 foot and is rated for a 60 HP. the prop on the 25 is currently a 3 blade 15p. i run about 25mph with me in boat (250lb)..and batterys and gas...equipment etc. i would love to upgrade to a 60 but money is short as of now. Wondering if a 4 bladed 15p prop would give me more speed...

 

[hwsiii]

Re: 25hp prop selection

Davey, you will need a tachometer in order to make an intelligent decision about which prop you need for your boat.



H

 

[steelespike]

Re: 25hp prop selection

H is right you really can't make a prop selection without a tach to know what rpm the motor is at now.Is the tracker a bare bones utility or full floor,live well console etc.? I would say the 15p is way off unless it is a really light boat.I think it should be around a 12p.perhaps less if a heavy boat.A tiny tach is easy to install and reasonable or perhsaps you could borrow a shop tach.Your max rpm needs to be about 5,500 lightly loaded.

 

[DaveyHAZZ]

Re: 25hp prop selection

Okay thanks for the educated info. My tracker is a fully loaded,full floored,carpeted,livewells,console,etc. its a full blown boat.batterys and gas too.


How can i install a small dash tach? id love to do this just don't know how

 

[DaveyHAZZ]

Re: 25hp prop selection

Say i did need a 12p, would a 4 bladed be better then a 3?

 

[trendsetter240]

Re: 25hp prop selection

Say i did need a 12p, would a 4 bladed be better then a 3?

Yes a 4-blade would be better as it would provide more blade surface area to help get the heavy loaded boat up on to a plane.

As mentioned, it's a best guess only without RPM and WOT numbers. I would guess a 12p 4-blade would be in the ballpark. That is assuming your motor is newer than 1984.

 

[DaveyHAZZ]

Re: 25hp prop selection

motor is a 1991 johnson 25hp..if anyone can tell me how to hook up a tach and where to buy..(i have an automotive tach,dont know if itd work) and also would like to add a speedo. thanks all much appreciated

 

[steelespike]

Re: 25hp prop selection

The tiny tach uses an induction pulse with a special wire from a plug wire.not sure if dash install is a possible there is a web site.Speedo is nice but are not real accurate.GPS is better.

 

[DaveyHAZZ]

Re: 25hp prop selection

thank you... do u ahve the website? thatd be great. as of now im staying with the 25hp.. but as soon as i can get some cash ill be maxing it out to a 70hp..so for now i just wanna make the most of it..

 

[hwsiii]

Re: 25hp prop selection

Davey, here is the site.

http://www.tinytach.com/tinytach/index.php



H

 

[trendsetter240]

Re: 25hp prop selection

thank you... do u ahve the website? thatd be great. as of now im staying with the 25hp.. but as soon as i can get some cash ill be maxing it out to a 70hp..so for now i just wanna make the most of it..

The website is www.tinytach.com. Also if you search for "tiny tach" here on the forums you will find a ton of posts about them.

 

[steelespike]

Re: 25hp prop selection

I have a feeling based on your boat description you will need a 10" pitch but get us some numbers first.

 

[Kamdyn]

Re: 25hp prop selection

I am running a 10.3x13 pitch prop on my 1997 Johnson 3 cyclinder and she runs pretty fast, You are already running a 10.3x15 pitch and thats as fast as she goes. Its only a 25H Davey and the bigger the prop you will get more thrust(Speed) and the smaller the prop you will get more torque but you will lose a bit of speed. Goodluck with your decision and let us know what you decide.

 

[hwsiii]

Re: 25hp prop selection

Davey, I thunk you are going to find out that you are turning less than 4,500 RPM at WOT.



H

 

[DaveyHAZZ]

Re: 25hp prop selection

arent thanks. wouldnt u want the motor to be running less rpm? i mean say i have 15p and i run 4000. and go 25... why would i want a 12p and go 5500?

 

[steelespike]

Re: 25hp prop selection

Forcing your motor to run below it max rated rpm is called lugging.
this can cause premature engine problems especially on todays doctored fuels Read that "ethanol" Your overall performance will be better as well.
At wot(wide open throttle) your 25 will use about 2.5 gph(gallons per hour)
whether at 4000 rpm or 5,500.With the 12" prop it will plane quicker,saving fuel,
with a load it will go faster ,saving fuel,It will likely stay on plane with less throttle,
saving fuel. If its easier for the motor to do these things its less stress than forcing it to run below its rated rpm.

 

[DaveyHAZZ]

Re: 25hp prop selection

alright makes sense. one more ?.. how would a lower pitch prop achieve more speed? because of the rpms? and right now im running a 10x15p

 

[trendsetter240]

Re: 25hp prop selection

alright makes sense. one more ?.. how would a lower pitch prop achieve more speed? because of the rpms? and right now im running a 10x15p

Imagine you are driving your car/truck up a hill in 4th gear. The engine is bogging down a bit and you can't go any faster even when you put the gas pedal to the floor. You then gear down to 3rd gear. The RPMs increase and the car is able to go faster up the hill.

This is exactly what you are doing by lowering the pitch in your prop. Changing to a slightly lower gear.

 

[DaveyHAZZ]

Re: 25hp prop selection

okay.. so i gotta find what my current RPM's at WOT are with this prop...

 

[pootnic]

Re: 25hp prop selection

I run a C1652V crestliner,pretty much bare bones,with a 30hp tiller.
I use 2 props a 11 and 13 pitch.The 13 is fine by myself and gear but if
I take acouple people and gear I normally put on the 11 to stay in a good rpm range.
I have a tiny tach,real easy to hook up and you could dash mount if you like.
Ask for more wire if you want to dash mount,pretty sure they do that for a few bucks more.
I'm thinking your 15 pitch is alittle much,although your speed seems pretty good.