How to find correct prop specs?

[wormboy]

I am worried that I am "over-propped" on my 1989 Evinrude 150, because of low WOT rpm readings. I am trying to borrow a hand-held tach or timing light w/tach to check my tach reading (BTW-- is there any problem with using an automotive one with the CDI ignition?), but was wondering how someone determines what propeller is appropriate for the boat and motor to get the approp WOT rpm range? Is there a chart somewhere or website? The motor is an E150STLCEM on an 18.5 ft center console w/ max load of 2000 lbs-- i use it mostly for freshwater fishing for lake stripers, but also pull the kids on a tube with it sometimes. Any advice is greatly appreciated!
Also-- in case the loaner tach doesn't show, is there a way of checking the tach with a voltmeter or multimeter to see if it is operating correctly?
Thanks!!

 

[Crownie2]

Re: How to find correct prop specs?

I saw a prop application chart at an Evinrude dealer one time. That was awhile ago, I don't know if they still have them, but you could check.

Bob

 

[wormboy]

Re: How to find correct prop specs?

Good idea-- amazing with the internet how we forget the old ways of getting info, like calling a danged dealer! I may even use my landline instead of my cellphone-- just for old time's sake.
thanks!

 

[imported_vtwin]

Re: How to find correct prop specs?

wormboy,
I have an 1989 140 Vro Evinrude on a similar boat, 19 ft and approx 2000lb with a small cabin.
My prop is an 13x19 and it pulls this boat very hard, and takes it to 47 mph on gps with 5700 rpm.

I never tried, but i guess it will take an 21 pitch prop also. Top speed will probably increase, but doesn't pull the toys as hard...

My prop is an original 3 blade aluminum.
if you want speed, try 21. If you'd like it to pull hard, try 19

Good luck

 

[wormboy]

Re: How to find correct prop specs?

Hi vtwin
thanks for the post-- i was finally able to find the numbers on my prop-- it is a 14 X 24! No wonder my WOT rpm has only been ~4000. thank God for this froum or I wouldn't have even thought to think about this as a reason.....
I'll look into what is recommended by the dealer-- my guess is that your set up is right about what i am looking for-- but do you think i should stay with 14 diam? This gets back to the main question about finding a chart on this stuff!
Thanks for the comments and suggestions!

 

[jaycozer]

Re: How to find correct prop specs?

Iboats has a prop suggestion/selector that you could use by simply plugging in boat information. Also www.mercmarinepropellers.com has a prop selector that uses your boat info to give you suggestions. You get a little range of pitch and blades but they along with some threads here have helped me determine I need a new prop because I was overpropped on a boat I bought used.

 

[wormboy]

Re: How to find correct prop specs?

Thanks jaycozer-- i found it. I also found info that suggests that the rpm can change 200 for each change in prop pitch-- which means that if I want to go up 1600 rpm, I'll need to go down in pitch from 24 to 16.
One other question-- the prop I have on is 14 in... should I stick with approx 14 (all I'm finding is 14.25-14.5) or go up or down? The prop chart seems to think I can get away with 15", and there is currently 1" of clearance with the lower unit, meaning top diameter is less than 16". Any recommendations?
I'll be happy to add the dunce icon to this thread if these are all obvious questions!!
Thanks.

 

[jaycozer]

Re: How to find correct prop specs?

I am a pretty new guy w/Cadet staus like you. What I am finding is I'll probably be going from a Merc High 5 21 Pitch 13.25 in 5 blade to the 17 Pitch version. Or I'm looking at M. Revolution 15 or 17p 14.65 inch 4 Blade. The length will affect performance as well and it seems from the research I've been scouring through it is no easy choice. The shape(cup) and materials all affect perf. Ex.- If I go four blade I'm looking at the Merc Revolution SS 15 or 17 pitch. If I choose Alluminum over SS the Merc Alpha 4 in 18 pitch seems the choice because the flexibility factor in Al. I am thinking I want to start anther thread to help me fine tune my choice. I have a Maxum 19 ft sterndrive w 5.0L 220 HP that I expect to ski/wake/tube and part time fish of course.

 

[walleyehed]

Re: How to find correct prop specs?

vtwin, just so you know, the engine in question has a completely different gear ratio, and uses much larger diameter props than yours.

There really is no chart for a specific engine on a specific boat...it just doesn't work that way.
I think you'll end up around a 19P and don't worry about diameter...I have the same lower unit and it will handle a 16" prop.

 

[wormboy]

Re: How to find correct prop specs?

Thanks Gents. Just got back from a marine supply for a carb rebuild kit and asked while I was there-- the guy seemed to think that i didn't want to go below 19p, and that would help w/some of the low WOT rpm, but not enough. I am borrowing a timing light w/tach to check if the tach on my boat is accurate-- which gets to a quick point, Kenny, if you are still here: if I have the boat in the water and check the WOT rpm w/out it in gear, should this approach the rpm specs in the book-- in other words, shouldn't the engine get up to near 5600 w/o load if the prop is most of the problem (its maxing at 4k now)?
Thanks!

 

[wormboy]

Re: How to find correct prop specs?

I realized this last question was a bit dumb-- about ulsing at WOT out of gear-- so don;t bother posting a reply to this.
thanks

 

[walleyehed]

Re: How to find correct prop specs?

I have to reply... Just to save you some possible trouble..
Never exceed 2000RPM, no-load. The engine CAN continue to run even with the key off, plug wires removed, etc....Only way to kill a run-away is remove the fuel source and by then, it may be too late.

 

[imported_vtwin]

Re: How to find correct prop specs?

Kenny,
I'm only telling that my boat with the similar weight and a 140 hp has a 19 prop.
Wormboy has a sort of reference now..

I sure know that a 140 is not a 150 and that the gears are different, but even if they were similar; you always have to trie out a prop, because every boat is shaped different.

But, you do think he needs a 19 pitch too i see. Even when it doesn't work that way..

 

[walleyehed]

Re: How to find correct prop specs?

Too many variables to discuss on why they are different.
In this case, yes, it appears they will be close in pitch.
Take the same boat/engine combo with a jackplate and 7-10" of setback and it may spin a 21-23.
Both engines require the same WOT RPM..with that being said, your prop is spinning 2950 RPM at 5900
the 150 is spinning his prop at 3155 RPM at 5900.
200RPM (prop) faster and MUCH more blade area...that's the difference.