I have no clue

[Thumperrr]

Hi men,I think I have a low speed problem.....this is what I have: 16 ft Lowe Roughneck(utility) 1-5 gal. gas tank,a starting battery,and an'05 40 HP E-tec the numbers stamped on the aluminum prop are 14X13 my top speed is 27.4 MPH (GPS) I need more speed to get off the lakes in a hurry.All the stores I've gone to have 13.25" props ,and the largest one I've found is 13.50"...the reduced dia. will make the prop spin quicker..right? if so then I'll need to go to a higher pitch...how much higher can/should I go? 2-3-4? I was hoping this engine boat combo would be good for around 35 MPH,but I'm a long ways from Kansas... Dorothy thx Thump

 

[pootnic]

Re: I have no clue

You really need a tach to get the right prop,without one it's kinda a crap shoot.
I do agree that it seems your going alittle slow for having a 40hp but with a gear ratio of 2.67 those 40hp are kinda torque e.
Does it jump right on plane?
If your going 27.4 mph,with that size prop(13 pitch)and gear ratio,I'm thinking your rpms might be alittle high(above 6000+)maybe even higher depending on slippage.
Just a guess(tach is what u need)a 15 should get you around 30 at 6000rpm,you might even have to go higher in pitch.

 

[steelespike]

Re: I have no clue

I think you need much more pitch. I feel at least a 17" pitch. 17" Don't worry about the diameter it will be very likely smaller than the 13"
If intended for your motor the diameter will be correct.
I think your 13" is probably over reving so I would stay away from wot.

 

[Thumperrr]

Re: I have no clue

Come to think of it ,it didn't really sound like it wanted to sit at WOT,ok I'll stay away from that area for now,I'll try and jury rig an auto tach to it and mount it on the seat across from me,to see what speed is at what RPM....P.O.1st class...yes it jumps up on plane at 17 MPH(GPS)it has good torque down low,it just seems to peter out above 3/4 throttle...do these engines have reed valves? or are they direct injection? oops may be the wrong forum for those questions. thx in advance Thump

 

[steelespike]

Re: I have no clue

The Etec is a direct injection.It has a numerically high gear ratio 2.67.
A quick calculation indicates about 6600 rpm at 27.4 with the 13" pitch.
Ouch! Max rpm is 6000.

 

[jestor68]

Re: I have no clue

The Evinrude prop selector comes up with a 17" pitch for general use.

 

[steelespike]

Re: I have no clue

The Etec site performance tests specifications list rpm 04,-12 at 5000-6000 some years 5500-6000.
Some of the same year being 5000-6000 others 5500-6000 I think that was tester error/discretion. Tests don't list the 05 but I think we can assume at least 5000=6000.
All the tests used a ss 17" prop producing speeds from30.2 to 35.1. rpms from5400-5825.
Glass,aluminum,and inflateables. Fastest was a 500 lb glass flats boat.A 973 lb glass skiff was almost as fast as a 420 lb inflatable.

 

[Thumperrr]

Re: I have no clue

Thank you men ,you just pointed me in the proper direction...I was thinking a 17" SS now all I have to do is decide which of 6-7 different models from 4-5 different makers I want..I've printed out all the info on this thread for my future reference as I honestly didn't know what the final gear ratio was...but I do now....I'll just hop along over to the prop area and gaze at all the shiny blades over there....thanks again Thump

 

[Thumperrr]

Re: I have no clue

Just as an update,you were right on with the 17" prop vs the 13 that was on it....now I travel at 31.1 MPH(gps) vs 26.4 I may venture up to a 19" pitch ...the motor is not straining like it sounded like before with the 13....I do have porposing that I am concerned with,but that's not for this area of the forum...thanks again for all the help you all have given me Thump/Bob

 

[82rude]

Re: I have no clue

just for your info guys unless the 40 is radically differnt from the 60 they have a rev limiter on them.when mine hits 6250 you hit the limiter and thats as far as your going so almost impossible to over rev those motors.for my particular motor i use a 15p as i normally carry lots of gas to camp and other stuff ,17p max for light loads .my boat unloaded is approx 550lbs. how much does your weight?you need a tac to make sure your running properly ,lugging a motor is just as harmful as over reving.also start adding people you may find that fast 40 turns into a slug.

 

[steelespike]

Re: I have no clue

A tach is an excellent suggestion.You can really get set up right.
Is the antivent plate(just above the prop) about even with the bottom?
Raising the motor might help with the porpoising and could add a little rpm and speed.
sometimes with manual trim one hole isn't enough and the next is too much.
You can buy or make wedges to add or subtract a half a notch.
Maybe you can move the tank forward.

 

[Thumperrr]

Re: I have no clue

I believe my porposing is due to too little weight in the bow or fore area,I had a 14 ft utility with a 20 hp merc on it and never had these problems with keeping the bow down...I'll add 2 trolling batteries in the bow area and see if that 160 # will make a difference...barring that I'll just have to get a really cute female mate to sit up on the bow seat