tunnel question

[boatermike]

so, experimentation is the key. I guess i knew that.In theory isnt a cleaver the choice ? but experienced people also say chopper.
I dont need bow lift thats for sure.
something i really wonder about is how much pitch?

i appreciate the input guys, thanx

[rivalguy]

I think the key to your pitch question lies in your RPMs which you don't know...


Maybe try using a prop calculator to estimate your RPMs (guessing at your slippage), and go from there.

Other people her can tell you where you should optimally be revving at, and go from there.....I'd spend a couple bucks and get the tach though.


prop calculator

[Dukeofchippewa]

Originally posted by boatermike
so, experimentation is the key. I guess i knew that.In theory isnt a cleaver the choice ? but experienced people also say chopper.
I dont need bow lift thats for sure.
something i really wonder about is how much pitch?

i appreciate the input guys, thanx

Pitch depends on RPM, speed, engine height, & slip. Start with whatever you've got, keep track of all above, then let us know.

[boatermike]

and thats the problem...............i dont have instruments. I know its dumb to be blind and i will have instruments next year. I plan many changes. After much studying of the scream and fly forums I have a huge list of things to be done to" trouble".
The most puzzling change left to decide is the propellor.
Lets say for the sake of conversation that i have not yet driven this boat and it has no prop.In fact the current prop is so lame i should sell it for scrap metal.Does anyone have a suggestion as to what prop i might select as a starting point?

[boatermike]

this prop calculator stuff, doesnt it require that i know the gear ratio?Well i dont know what the gear ratio is.Would be cool to estimate my rpms with a 19p at 55 mph.

[rivalguy]

Yes it does.

Someone on here should be able to help you with the ratio for your make and year.

[Dukeofchippewa]

on a prop til you get a tach. No one can tell you anything without knowing RPM, speed, & height.

[mendo]

Pull the spark plugs.
Put a mark on the flywheel.
Put a mark on the prop.
Slowly turn the flywheel by hand and count the turns.
Flywheel turns 2 times to prop turns 1 = 2:1 gear ratio.
Sometimes you may have to turn it a few times until you get a real even number on the prop. Then do the math.

Hope that helps.

[boatermike]

are there that many different ratio's for a 1974 johnson 135 hp v4?

[boatermike]

i think its safe to say that my vanilla 19p is not enough prop. The acceleration is intense, and im sure more pitch is needed.I,m 4sure gonna by a prop from the forums before i get to drive this boat again in the spring.As i look in the forums i see a wide range of props that i could afford.I have no dreams of finding my perfect prop the first time.
So.....dreamy eyed i scan the forums asking myself again and again.What pitch? what pitch????On one hand people with three cylinders on little boats are runnig 30p cleavers.On the other hand people with 250 hp are running 23 choppers. Some people obviously want hole shot and others want absolute top speed.This is all complicated by the fact that it looks like i can run merc inline props but not all of them.
I dont mind spemding a buck or three for a prop but i wouyld feel might deaf dumb and blind if i bought a 21 when its obvious i could turn a 32.
Could anyone narrow it down more?

[northeastcat]

You need to keep safety in mind as well as anything else. No trim no jack plate could equal disaster. Some small tunnels are known for there unique ability to blow over, not a fun Saturday to say the least if it happens.
Now , my tunnel hates cleavers. I know some people run them but I have tried them and dont like them at all. I would say you dont need a chopper where you have said you have great bow lift already and it would seem that you are packing air nicely already so go for a semi type cleaver like an ET , I would be hard pressed to believe that you wouldnt like it. If it was me I would look for a 22 pitch , if you dont like it , re-list it for sale and get something else. That would be the only thing I could tell you at this point. Everything else you are asking would take a damn good crystal ball without having more info about RPM , MPH , gear ratio and some better pics of the hull and possibly some running shots to show how it runs at speed now too.
Hope this helps , NE Cat

[SportJ-US-1]

The gear ratio us 2:1, so that's a known. The prop is a 19p. Now you need the speed and rpm and you will know slip. Guessing at the slip will almost never work, as changing any part of your setup will change it. Insturments are required to setup your boat. Minimum are (1) tach, (2) Speedo( a good one not Merc or Omc junk) (3) water pressure guage. I would hazzard to say the 19 isn't enough and you will need at least a 22 to 24 stainless so you can get the engine up where it belong. I once own a Magnum Missle and the 1500XS with a 20p chopper would turn 7400rpm and 58mph. With a 24p chopper the motor turned 6900 but the boat went 64mph. Found out later that the motor max itself out at 7400 rpm, otherwise that's all it would turn, even unloaded.

[Fulltilt]

boatermike,

I'm not an expert but, I run a boat similar to yours. 15ft light full tunnel with a V4. My 20" raker is a good all around prop, but I turn too many rpms and run with the bow pretty high. I need more pitch with less bow lift, I'm guessing in the 23/24 range, so you can probably turn a 26' small blade chopper or cleaver. On the other hand i've got my motor jacked way up and know what rpms I'm turning. I think chinewalker said DAH makes a good prop for OMCs and knows alot about which one is good for which application. If you search some of the threads I'm sure you can find their phone number. I hope this helps.