1998 Evinrude 70hp @ WOT

[oceansbreeze]

On my 1999 Princecraft, this 1998 70hp Evinrude at WOT was getting about 5400 rpm and top speed of about 32mph - with full tank, and only me in boat.

I'm still reading and trying to understand how pitches work, in all my years of boating, I have never had to change a prop. (I am still looking for a good tutorial on how, if anybody can point me to one??) as I do keep a spare prop on board.

My spare prop says 14x17 so I think that means 14" diameter and 17" pitch? The mounted prop says the same... they are identical.

Generally I cruise alone.... no skiing ... I may go skiing once a summer.... I just want to get up on plane, and maintain a good cruising speed... with lower rpm for better fuel economy...

Is 5400 rpm about what I should expect? Is it worth moving up to a higher pitch for speed.... which would give me a slower hole shot, but higher speeds? Some advice on this? Thanks..

 

[petryshyn]

Re: 1998 Evinrude 70hp @ WOT

Sounds like you're hitting the sweet spot at 5400. I'd leave it alone.

 

[tashasdaddy]

Re: 1998 Evinrude 70hp @ WOT

actually a 1997 should be turning 5500 - 6000 wot. i suggest smart tabs to help get on plane quicker, and stay on plane at slower speeds. but for the prop question, i am moving this to the prop forum.

 

[countvlad]

Re: 1998 Evinrude 70hp @ WOT

On my 1999 Princecraft, this 1998 70hp Evinrude at WOT was getting about 5400 rpm and top speed of about 32mph - with full tank, and only me in boat.

I'm still reading and trying to understand how pitches work, in all my years of boating, I have never had to change a prop. (I am still looking for a good tutorial on how, if anybody can point me to one??) as I do keep a spare prop on board.

My spare prop says 14x17 so I think that means 14" diameter and 17" pitch? The mounted prop says the same... they are identical.

Generally I cruise alone.... no skiing ... I may go skiing once a summer.... I just want to get up on plane, and maintain a good cruising speed... with lower rpm for better fuel economy...

Is 5400 rpm about what I should expect? Is it worth moving up to a higher pitch for speed.... which would give me a slower hole shot, but higher speeds? Some advice on this? Thanks..

ok.. your spare prop is 17 p good... how about the prop that is on the boat right now????

it is not hard to change a prop... make sure you have an extra cutter pin just in case you have to change the old one.....

if your rpms are 5400 at WOT you might wanna go up 2 pitch....

how far is your cavitation plate sit from the bottor of the hull?

 

[hwsiii]

Re: 1998 Evinrude 70hp @ WOT

Oceans, if you buy the same make and model of prop you have now in a 19" pitch you will lose approximately 500 RPM, and that will put you below the minimum recommended WOT operating range for that motor, as it is designed to operate between 5,000 and 6,000 RPM, and that is not good. It is better to run in the top 25% of the WOT range, and on your motor that would be about 5,750 RPM to 6,000.
In my opinion I would check to see if both props are the same make and model, and I would try the other prop just to see if there is any difference in blade geometry that might give you an increase in speed.
After doing that I would then put the prop on that gives you the most RPM and speed with the least prop slip, they can be mutually exclusive of each other.
A good idea is to see if the motor is as high as you can raise it on the transom, a good indication of this is what dhadley says, if you can trim the motor out all the way without ventilating, you can go higher. Then I would start raising the motor to try and get an increase in RPM and speed from height. The higher the motor is on the transom normally the more RPM you can get out of the motor and thus speed, and it cost nothing except time. But after raising the motor also try making some sharper turns to make sure you don't start ventilating bad, when you get to the point where it starts ventilating in harder turns you are high enough in my opinion.
Here are the numbers for prop slip on the prop you are using now, if your gear ratio is 2.42:1 please verify the WOT RPM and gear ratio.


Prop Slip

And that is a good prop slip for an aluminum prop.


H