Propeller Gap causing prop slippage in water

[John Vinzant]

1980 OMC 140 with a 400 Stringer, came with a 13x15p prop, can get 4800 WOT, GPS had speed at 19 MPH. With engine running sounds like the engine has no load on it, lots of cavation at cavation plate. There is a large gap about 3/8 in between prop and lower housing. plus the prop sits about the same distance away from the housing.
​Bought a 13x19p to see if it would help, the gaps on the new prop was not as pronounced. Got 3800 WOT at 23 MPH by GPS, and you could here the engine was under a load. Checked thrust washer, fits both props.
​Thinking that the engine exhaust is coming around the outside of props instead of going thru.
​Is there a defuser ring that I may be missing or can you even purchase one?
Both props are 3 blade aluminum..

 

[Scott Danforth]

depending on the boat, you should be doing about 40mph at 4600 RPM with a 19 pitch prop. that is what my 17' Avanti did with a 1984 3.0/stringer (wet weight about 2300# with fuel, gear, people). I also used a 15pitch for pulling skiiers

something is wrong with either your motor or your props, or you have a really big/heavy boat.

what size boat
what is the part number of your props
Are these OMC/Evinrude props? (the stringer 400 used same props as the V4 outboard)
when was the last time you did a compression test and tune up.

 

[alldodge]

You defiantly have some large prop slip going on there (15-47% and 19-49%)
Since your prop is not sitting all the way down I'm thinking you might not have the right thrust washer

http://www.iboats.com/BUSHING-THRUST/dm/cart_id.581237840--session_id.645168595--view_id.1487714

 

[John Vinzant]

Boat is a 25 Ft. 1980 Lakescraft Beachcomber, single engine Pontoon w/ two logs.

 

[Scott Danforth]

being a pontoon changes things

pontoons are displacement hulls until you get enough power to get it up on plane. that 3.0 isnt enough, although it may be close. 19P may be too much for that setup. thinking the 15P or 17P may be better.

 

[alldodge]

Hey Scott, I assumed the drive ratio was a 1.81, and if that is the case, there is way to much prop slip. Even if its 2.20 then its still to much slip, wouldn't you agree?

Do you know what the drive ratio is?

 

[John Vinzant]

No numbers on engine to compare to, No tags found on Engine. Outdrive Model 981871, found that tag....Found upper ratio 21.18, Lower 13.26 total .61, overall 1.64 found in Seloc Book
​

 

[alldodge]

If it is 1.64 that makes it even worst with a 54% slip.

 

[John Vinzant]

No Title

 

[alldodge]

That is a lot of gap, and I would say you either have the wrong prop or wrong thrust washer, and I'll bet on a wrong prop

 

[Scott Danforth]

those are the WRONG props for a Stringer / V4 gear case PERIOD. they look like yamaha or mercury props which DO NOT work, yet can be made to fit

the prop needs to fit tightly within the gear case. the step in the gear case matches the step in the prop. this makes sure the exhaust gasses go out the prop and not around the prop causing cavitation

the correct prop would look like this:

the correct props would fit like this

 

[John Vinzant]

That's what I was thinking. The first photo is the prop that came with the boat after I bought it. the second was purchased about 6 months ago, going by what the prop book said.
Have not found one on similar to it on ebay or CL.

 

[Bondo]

Ayuh,.... Donno where yer gonna find the Right prop, but the 2 ya have are the Wrong props,.....

Just one of the issues when runnin' a stringer drive, a 400 stringer no less,.....

 

[Scott Danforth]

I got used Johnson/Evinrude props for the V4 off of ebay and craigslist. both were stainless. I think I paid $40 for the 17p and $25 for a 15p. granted, that was 10 years ago.

you have to go off of what OMC recommended for props for the stringer (or the V4 johnson/evinrude), and not what a prop company recommends. most prop companies dont even list the stringers anymore and try to sell you props for a cobra drive. not the same

here are a few stringer props on Ebay

http://www.ebay.com/itm/OMC-STRINGE...ash=item360de5f5e6:g:W8IAAOSwEzxYQJx~&vxp=mtr

http://www.ebay.com/itm/13-1-2-X-15...ash=item3ad5183dc5:g:NUMAAOSwA3dYJMml&vxp=mtr

http://www.ebay.com/itm/OMC-Outboar...ash=item3d2dba9745:g:8cEAAOSweWVXeqm7&vxp=mtr

 

[proshadetree]

Ebay or look for a shop that reworks props. Alternatively you could check with marine repair facilities, most have a stash of used parts.