want more top end

aintmisbehavin · Oct 24, 2009

Right now I'm running a 14x17 prop

speeds and rpm's as follows

31mph @ 5200
25mph @ 4500
21mph @ 4000
17mph @ 3500

This is an 1977 19' renken, w 1976 johnson 115

runs good, would just like to get going a little quicker, what prop change if any should I make?

wilde1j · Oct 24, 2009

Re: want more top end

I assume WOT = 5200 RPM. If so, drop to 15" pitch and you'll get better hole shot and the WOT closer to 5800, where you should be @ WOT.

You may not have higher top speed with the change, but you'll surely get up on plane quicker.

R.Johnson · Oct 24, 2009

Re: want more top end

Start with boat set up. Remove all the weight you can.

steelespike · Oct 24, 2009

Re: want more top end

He forgot to mention prop is pretty dinged up speed and rpm could suffer.
13 3/4 X 19 was standard prop of course the final selection could be different. a 17 is certainly a reasonable selection for the application.
1420 lb dry.

emdsapmgr · Oct 25, 2009

Re: want more top end

At a 17, running those rpm's you are still at least one prop pitch off. You need to get the engine up to 5500-5700. Try a 15. Check to make sure the anti-ventilation plate is not running submerged, causing extra drag and poor performance.

kenmyfam · Oct 25, 2009

Re: want more top end

Is this a new outfit to you or have you had it a while and it has always performed the same ??

aintmisbehavin · Oct 26, 2009

Re: want more top end

If I try a 15, do I keep it at 14" diameter? This is an old boat that I've had to 2 yrs. Just recently installed a tach to know what I'm spinning at.

wilde1j · Oct 26, 2009

Re: want more top end

Diameter doesn't change (and has little effect for small differences).

aintmisbehavin · Oct 26, 2009

Re: want more top end

I'm also running a hydro foil, I removed it a couple weeks back and it only improved my speed by 1mph.

I ordered a 15 tonight. We'll see if it makes a difference. Its got to be better than a bent and chewed up 17.

And it should get me a little higher in the rpm range.

R.Johnson · Oct 27, 2009

Re: want more top end

Your outfit make's for a very nice family boat. Just prop for the way the boat is normally used, or about 5500 RPM. With a boat that size, and weight, your never going to make it into a fast performer. Just use it for what is was intended for.

aintmisbehavin · Oct 28, 2009

Re: want more top end

That is the intent. You can't exactly polish a turd, but you can help it along with adding a few things. I'm ready to upgrade to something within 5yrs old, but my wife loves this old one. So I have to get it to where I want it to be happy. So the tach, speedo and prop were the few things I added to watch what we were doing.

aintmisbehavin · Oct 31, 2009

Re: want more top end

34mph @ 5050
30mph @ 4850
25mph @ 4050
20mph @ 3600
15mph @ 3000

are the new numbers with the 15 pitch prop, I was expecting a little more RPM's, but I got a little more top end and not spinning as fast.

wilde1j · Oct 31, 2009

Re: want more top end

Something's not right. No way you would be getting LOWER WOT RPM with 2" less pitch, unless something in the setup changed (motor height, etc.). RPM should have gone up at least 300 to 400.

kenmyfam · Oct 31, 2009

Re: want more top end

Cupped prop ????

aintmisbehavin · Nov 1, 2009

Re: want more top end

wilde1j said:
Something's not right. No way you would be getting LOWER WOT RPM with 2" less pitch, unless something in the setup changed (motor height, etc.). RPM should have gone up at least 300 to 400.

I removed prop and installed new, put in water. nothing changed. I was shocked at first. Then I messed with trim.. I only have the pinned trim, but it was working best at the highest setting. Usually I have it in the middle.

The prop got rid of my low end vibration.

wilde1j · Nov 1, 2009

Re: want more top end

I would try a 13" pitch ... your RPM is way too low.

aintmisbehavin · Nov 1, 2009

Re: want more top end

I choose the 15 from everyone's recommendations. The boat ran great and seemed to handle better. I wasn't sure if the 13 would have put me too high in the rpm's, but after staying the same, I think it would had been ok.

Might grab me a 13, but dropping another $100 on a prop may not happen just yet.

On the other hand. $100 is pretty cheap for another good prop and to have a backup, my original 17 is trashed now that I compare the two.

wilde1j · Nov 1, 2009

Re: want more top end

If your motor is only turning 5050 @ WOT, you can expect significantly reduced life. I would try raising the motor first based on your other thread before buying another prop.

reeldutch · Nov 1, 2009

Re: want more top end

before changing anything and spending moere money and time and dont know anything, start from the beginning.

make sure the engine performs as it should.
compression ok?
ignition crisp?
fuel pressure and carburators in good shape at top performance?
engine temp around 140*f

if all these things are where they should be, than look at the setup.
normaly we set the anti cavitation plate even with the keel of the boat. you start from there.
i think an alluminum prop 13 3/4 X 17 is a good starting point. forget about the banged up prop.
a 13 3/4 X 15 should defenatly raise your rpm by minimum of 200 rpm.
if not something is wrong.

make sure you dont mix alluminum with stainless that will change a lot.

the key is change one thing at the time.

kenmyfam · Nov 1, 2009

Re: want more top end

Seems like a set up issue. Photo of the stern with the cav plate would be a big help. May need to raise the motor up some.
I will ask again.....cupped prop ????

want more top end

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