problems achieving max speed

[(='_'=)]

hey. i have a 379 Javelin from 1994, with a 150Hp Johnson. the boat is about 18' long. the prop reads 14 1/2 x 24, its stainless. i have no jackplate, and a stingray hydrofoil. 

i have read my max speed should be about 60-65 MPH, however the most i have gotten in my gps is 50 mph, with 2 people, no load. with 3 people and fishing tackle i can get 46-48. i normally cruise at just enough speed to keep on plane, as the lakes i usually fish are small. but i plan on going to a bigger lake where speed would be required to travel a longer distance, besides, i think having the right setup would be more efficient, even at lower speeds...

 

so, what should i do to increase that speed and efficiency??

[Further North]

What is the source for the initial speed claims?

There was an online report that my boat, rigged exactly as I have it set up, would run in the low 50s.  The only way that's going to happen is with 3 gallons of gas in the tank, completely empty otherwise and a skinny 10 year old as a driver.

I got about 4 MPH out of mine by raising the motor to the last hole, but still short of the low 50s.

You are right about speeds indicating efficiency...but I'd try to validate that speed claim first.

Steps to take - figure out what RPM you are running (your tach is likely off at least a bit) and make sure that is near the max RPMs for the motor...it's better to be a little short of red-line than over, for obvious reasons.

[Way2slow]

First, You didn't post any rpms on your motor at WOT.   I have a hard time seeing that setup turning a 24" prop anywhere near max recommended rpm with a load.  That can slow you down a huge amount.

The condition of the prop can have a big impact on speed.

Not know how the motor is set and not having a jack plate, that hydrofoil could be costing you a few mph. 

How much you over load the boat with your friends and gear, can kill huge amounts of speed, and with an oversize prop, can make it very difficult to get on plane. 

Then the condition of the motor.  If it has some weak cylinders, that can kill huge amounts of speed and hole shot.

[WIGuide]

x2 on w2s and further north. Take it out, run it, and find out what your RPM's are. Also, how much are you trimming when you're running it? Under or over trimming will cause you to under perform in the speed category as well. 

[(='_'=)]

thanx for your quick replies. 

first of all, my tachometer is not working, so i dont know my rpms, im already working on fixing it....

the speed claims i got from a facebook group of Javelin owners, seems like most of them run at least 60 mph.... assuming they are just bragging, how fast do you think a 18' 150 HP boat should go??

my prop is in as new condition... or well, it was up until last trip when i hit a submerged log... it got dented a bit, but im picking it up tomorrow from the shop, so it should be fixed as new again... so all my tests were with the prop without a dent or anything.... 

w2s why do you mention oversized prop?? i think its 14 1/2, pitch 24... or am i missing something??

the boat gest on plane quickly, and with 3 people and fishing gear i have gotten 47-48 mph, while with 2 people and no gear, i only got 50 mph... 

im still learning how to handle the boat, the way i do it is trim all the way down, and then accelerate slowly, once on plane, begin trimming up, gaining speed without accelerating... i really dont remember if i trim while accelerating to get on plane, its automatic and i havent noticed... once i get on plane, if i want to get max speed i just step on the hotfoot all the way down and trim up until i stop accelerating.... a couple of times i have began porpoising so i trimmed down a bit, it doesnt happens often though... 

i have used the boat for skiing without a problem, it gets on plane and pulls a skier easily, if thats worth something... 

[(='_'=)]

i found the prop by number 394753

and it says this:

 

• Manufacturer: Evinrude / Johnson / OMC
• Prop Family: Raker
• Part Number: #394753

• Rotation: Standard Rotation
• Diameter: ***/2”
• Pitch: 20”

 

 

i thought it was pitch 24?? because of the 14 1/2 x 24 written on the prop itself.... 

http://boatpropellers.iboats.com/Evinrude_~_Johnson_~_OMC-Raker-Propellers/394753/?cart_id=564368837

[Way2slow]

Without knowing the exact RPM, the motor is turning when at full speed, with the motor trimmed out properly and your normal load in the boat, anything anyone tried to tell you would be pure speculation. 

Knowing your RPM is a must, at least is before I can give any advise, because like I said, I think you are running to much prop.  If that boat was able to spin a 24" prop at 5,800 rpm, it would be running about 65mph and with that setup, that ain't gonna happen.

[Way2slow]

I think when you pick it up from the prop shop, you need to ask them.  I've never seen one missed stamped with the pitch.

I believe if you look at the last digit a little better, it's a( 5) that the corrosion is making you think it's a (3). 

[(='_'=)]

thanx! thats about what i have read, 5800 rpm at 65 mph is what people claim to be achieving... 

 

you mention "with that setup".... so, what would be required for my motor to turn the 24 prop at that rpm?? 

and if i were to change prop, which one would be better for what i currently have?? 

 

[Way2slow]

PLEASE UNDERSTAND!!!!!

The is no way on planet earth I can tell you anything about what to do about props or setup without knowing the exact RPM the motors is turning right now, with the current setup. 

Maybe one of these other guys that have a better crystal ball them me can, but I can't.

[Ski213]

Let me ask a dumb question. Is the number in the picture stamped on the prop itself or is that part a washer?  I'm thinking mine is stamped on the washer. If so, you definitely need to ask the prop shop what you have. I could be wrong on that but if I'm not I would think that the washer could mislead you as to you pitch. 

As w2s said the rpms are not an optional piece of info for good advice. When these guys are saying 65 is that GPS or speedometer speed?

 

[Bass newb]

My optimax  115 pushes me 51mph. 17.5' ranger 21p laser 2 prop. I would guess you should be faster.

[Ski213]

I know you're looking for a quick and dirty answer. You should be able to get the 60s. I had a buddy that had your hull with a 150. He was low to mid 60s. I don't remember the specific setup and unfortunately asking him isn't an option.  No clue what prop or setback or anything. I do remember that to get the 60s he had to do some real driving. Get that tach fixed and figure out for sure what your prop is and then you'll be able to get some solid advice as far as what you should be able to achieve and how to do it. Welcome to the top speed addiction my friend.  

[(='_'=)]

thanx!! ill have to fix the tach then before trying anything else...