Prop Identification

[KRH1326]

Hello All,

I have a 1976 OMC 235 HP (351w) Electric shift. I am not sure what the WOT RPMs are supposed to be. I would guess around 42-4500, but not sure. edit thanks to WO and B1235> Book says 4200 - 4600 RPM.

I had a prop ( they are the type with a drive pin, not splined ) on it that had been giving me a WOT RPM of about 4000 RPM. That prop spun the hub, earlier this season, and I switched it with a spare prop that I came across.

This new prop gives me 3000 WOT RPMS.

I didn't have both of the props in my hands at the same time, but when I took the new one out to the mooring and installed it, I believe that it was larger in diameter than the previous one. I just compared the one that slipped to a couple of others that I have and they all seem to have slightly different blades and shapes. My problem is that they are old and finding any numbers on them is proving to be most difficult.

I did not see any numbers or identification on the props.

Is there a way to measure the props? Diameter I can get, but is there a way to determine pitch? Just to figure out what I actually have?

If it helps, my ratios are:

Upper 21.16 Lower 15.23 Total .86 Overall ? 1.16

Thanks Guys

 

[WizeOne]

Re: Prop Identification

Take it to a prop repair shop. They can reliably check the pitch for you. They might even have some rebuilt props for sale as many people drop them off and never pick them up.

 

[KRH1326]

Re: Prop Identification

Ahhhh.....
Great answer.

Thanks Again WO

 

[WizeOne]

Re: Prop Identification

Not only can they tell you what you have, they can change the pitch if needed.

FWIIW, a recent inquiry to a local prop repair shop indicated that they cannot change pitch more than one point.

 

[hwsiii]

Re: Prop Identification

KRH, welcome to Iboats prop forum and we will try to help you as much as we can but without more information no one can help you, and I will tell you I need more information than anyone else. But if you would like my help fill this form out and I will help you as much as I can, if you would prefer to not go to this much trouble there are other people who will gladly help you.

Iboats Boat and Motor Info

1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the maximum recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make. manufacturer and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape a c ross the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches, use a board under the keel and stiking out to the anti ventilation plate for a referene
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. Make sure you trim the prop up until it starts ventilating and then just trim in until it quits ventilating. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.


H

 

[KRH1326]

Re: Prop Identification

Holey Moley, HWSIII, that is some list. Wow!!

I would like to try to get all of that, because I would definately like to set up for economy. It will take me a while to get this all as faithfully as possible.

But I will give you now, what I have and work on the rest.

This may sound silly, but not sure of the model. I believe it is express only because the weight sounds right.

1976 Winner Boats Express Flybridge.
http://www.iboats.com/Winner__Express_Flybridge__1976/bp/64b102048r2

-OR-

1976 Winner Sport Fisherman Flybridge http://www.iboats.com/Winner__Sport_Fisherman_FB__1976/bp/64b102056r1

24' length 8' beam 4200 unlaiden weight for WB EF & 2700 for WB SFFB
235 HP Rating
3-4 people and 40 gals. ( 62 max cap )
Used mostly for fishing, or hangin' out.
I think it's deep vee. How to measure deadrise?
1976 OMC 235 HP (351W engine) Electric Shift
235 HP Upper 21.16 Lower 15.23 Total .86 Overall ? 1.16
4200 - 4600 RPM WOT
Anti-ventilation Plate height ( can't give right now, boat is on a mooring )
I have trim tabs
Current prop gives me 20 mph by gps @ 3000 rpm WOT
I am at sea level
Motor has been tuned , carb rebuilt and compression tested dry.
I just stuck this prop on because I had it and it fits. The previous prop spun a hub. I think it is the wrong prop because I am getting a WOT of 3000 rpm.

I am just trying to get decent economy, and trying to get in the WOT range of 42-4600 rpm.

I will try to get the remaining info.
I have been trying to find winner boat photo's so that I can identify my model. She is a heavy, sturdy girl and the 4200 lbs sounds right on to me.

 

[KRH1326]

Re: Prop Identification

Was able to identify two of my props.

The one that spun, and needs the hub redone, was a Michigan Wheel PR 120. 14 x 12. That one was giving me a WOT of 4000 rpm.

A used spare that I have not tried yet is 381187 14 x 18. That seems to be for a smaller, lighter boat.

I have 2 other props to check. One is the one on my boat now. I suspect that it may be a 14 x 18 as well or possibly 14.25 x 18 or something like it. That is the one that gives me a 3000 rpm WOT.

And the second is an untried spare, on the boat.

I will look at those for numbers this weekend.

So far I am guessing that I really want a 12 or less pitch. What pitches can still be found? 11 10?

Thanks

 

[hwsiii]

Re: Prop Identification

With the numbers you gave your gear ratio is atually 2:1.


H

 

[KRH1326]

Re: Prop Identification

I don't understand the numbers or how to use them. I asked Howard Sterndrive for help with this ratio and he sent this:

"15/23=.652173913

(16 / 21) / .652173913 = 1.16825397

engine goes around 1.168 times for each propeller revolution

or another way to visualize it:
Engine going 1168 rpm
Prop going 1000 rpm

At 4000 engine rpm, your prop is going 3425 rpm

Those drives must run very low pitch props. A 16P would be for a light fast boat.
I dunno what heavy cabin cruisers would use.... 12P?"

 

[KRH1326]

Re: Prop Identification

PS -

HWSIII, thank you for help and mostly for your patience.

 

[hwsiii]

Re: Prop Identification

KRH, here is what you gave me andit is orret.

Upper 21.16 Lower 15.23 Total .86 Overall ? 1.16

21 / 16 = 1.31
15 / 23 = .65

1.31 / .65 = 2.01 This is your gear ratio.

Whyen you show them in the one you did you reversed the 16 and 21 gears.
I am assuming that was the right gear ounts. I don't know whih one is right but it also makes more sense with a 2:1 than a 1.16:1. Please verify, and you are very welome.


H

 

[KRH1326]

Re: Prop Identification

Upper 21.16 Lower 15.23 Total .86 Overall 1.16
Came from seloc & clymer. I know that they can't be trusted.

I just went to a reliable site http://hhscott.com/evinrude/props.htm
and they have the same numbers. They included:

.86 gear ratio total is "engine to prop"
1.16 overall ratio is prop to engine
31-52 speed range in MPH 20% prop slip engine @ 4000 rpm 12"-20" pitch

I am sorry but this is greek to me. I can tell you what all of the numbers mean on a welding rod, tho.

 

[Bifflefan]

Re: Prop Identification

:

Just sent you a PM.

 

[KRH1326]

Re: Prop Identification

TY bifflefan.

HWSIII,

Still trying to find ratio's and data, but keep finding those same numbers. Any ideas?

Thank you again.

 

[KRH1326]

Re: Prop Identification

WOW, you won't believe this!

I just went out to East Quogue, to a boat yard, because I saw that they had some OMC props that they were "giving away" for 40$ each.

I just got two 14 x 12 x 3 part number 382017, new in the box props for $80.

They are ridding their shop of alot of old stringer OMC stuff. Eighther they don't really know the value (eBay and such) or they are helluva nice people.

I stayed and BS'd with the owner and a mechanic for an hour or so. The owner came back out with new in packaging ball gear assembly with bearings and shaft and a set of shims, AND JUST HANDED THEM TO ME.

He took my name, number and address and told me he would crate up and mail whatever stuff he has for the electric shift as he goes through his wharehouse. He will even send his OMC factory manuals and what OMC tools he still has.

I almost fudged my shorts!!!

 

[hwsiii]

Re: Prop Identification

KRH, to be of any further assistane to you I need the orret gear ratio, please do it this way.

7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape a c ross the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor.

Here are the Prop Slip numbers using a 2:1 gear ratio and 1.16 gear ratio, whih one do you think is right, the one with 50% prop slip or 20% prop slip. And I am not sure either one is right, so be sure how many times it turns.

Prop Slip

And that was an exellent deal that you got on the props and the free things he is giving you.


H

 

[KRH1326]

Re: Prop Identification

Thank you HWSIII,

I will try to get that count as soon as I can go out and do it.

 

[hwsiii]

Re: Prop Identification

That sounds great.


H