Propeller convergence ring removal

[Cofe]

Here are a couple of pics of a 1990 evinrude 25 prop. The prop on the motor does not have the converging ring on the rear. The other stock prop is spun, and it has the ring. My questions are,,, Is the ring removable? Does a prop even need one?

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[steelespike]

Re: Propeller convergence ring removal

As I understand it the ring is to improve reversing by limiting exhaust from fouling the prop when trying to back.

 

[Texasmark]

Re: Propeller convergence ring removal

Back when the SST (first OMC Stainless prop which was black in color due to Teflon coating) came out (1970 something) it had a bronze ring on it that brought water into the slipstream, rather than flare out and enlarge the same. The diameter of the ring was roughly 1" wider than the prop tube. It was a convergence ring as it made the water converge into the slipstream.

They were just pressed on and you'd see about half the props in later years without the ring....obviously got knocked off by debris.

This one you show is a divergence ring that Merc used on their SS props. Later on mfgrs put the Merc type ring on props that went on OMC engines.

Other than what steel said, the other reason (it has been said) is to help prevent the prop from sucking exhaust from around the end of the prop and causing cavitation or ventilation which would cause the rpms to increase and boat speed to decrease. Some SS hp props don't have the flare at all. They just extend the barrel more.

Beins the old prop is not usable, get a chisel and hammer and gently see if you can tap it off. Tapping back on would be to put the prop down on a hard surface on a 2x6 board and with another 2x6 on top and drive it onto your new prop. Or just forget it if you are not currently having performance problems.

My 2c,
Mark

 

[Mi duckdown]

Re: Propeller convergence ring removal

If it were I. I would rebuild the prop with the ring, and keep the other prop in the boat for a spare. .02

 

[phillnjack2]

Re: Propeller convergence ring removal

Here is a pic of an early omc sst propeller with the teflon on but going rusty, then with it taken off and cleaned up.
Even with the stainless now cleaned up and looking semi shiny, you can clearly see the bronze ring talked about above.
Ive heard many bad things about these rings and many good things.
for now ill leave mine on as the prop is working very good and i dont have any problems with it.

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phill...:joyous:

 

[Texasmark]

Re: Propeller convergence ring removal

Here is a pic of an early omc sst propeller with the teflon on but going rusty, then with it taken off and cleaned up.
Even with the stainless now cleaned up and looking semi shiny, you can clearly see the bronze ring talked about above.
Ive heard many bad things about these rings and many good things.
for now ill leave mine on as the prop is working very good and i dont have any problems with it.

..View attachment 178407


phill...:joyous:

That looks exactly like the OMC SST (Stainless Steel Teflon...coated) prop that I put on my Johnny 125 back in '72 or 3, right after they hit the market. Was an excellent choice for me over the aluminum I had been running and the $185 I paid for it soon paid for itself in repairs (to aluminum props) that I didn't have to have.

I think the concept for the convergence ring was to keep exhaust from getting into the blade area and causing ventilation. On the Merc style ring, as the author has in his picture it is a divergence ring, was here first, not that it matters, and served the same purpose. I mean geez, OMC couldn't look like a Merc.....ohmygosh!!!!!

As I stated, I saw a lot of bass boats running the OMC props with the ring knocked off. I don't know if they got them knocked off in heavy timber fishing, or deliberately knocked them off thinking/getting another half mph of speed out of their rigs.

Mark

 

[phillnjack2]

Re: Propeller convergence ring removal

well my prop above was infact a sort of prototype race prop back in 1970/1971.
It was supposed to be used for racing from putney to calais and back again.
it was only used from back to putney, and was highly praised for its performance.
the prop then got put back into its box and not used again .
the prop was given to me by the original owner around 1998/9 and he told me i should
look after it as its a great prop.
Its only this year that i took it out of the box again and cleaned it up,it used to be horrible black
looking finnish with the teflon going a bit bad and a bit of rust here and there due to being stored in a damp place.
well now its getting used on my 1995 evinrude 60hp and gives a good turn of speed and digs in real nice.

and $185 back in 1973 was a hell of a lot of money ha ha ,be like $1,000 today easy.

i would keep a ring on the prop if possible,it cost the makers extra to put them on so they must of been usefull
maybe not at highspeed though, i realy am not so sure.



phill

 

[coolguy147]

Re: Propeller convergence ring removal

Do all SST props have these? Mine doesn't

 

[Texasmark]

Re: Propeller convergence ring removal

Do all SST props have these? Mine doesn't

I don't spend any time to speak of around OMC engines any more. Any of the convergence rings that I do see are on older props. Maybe Merc had a patent on the divergence flare molded into the rear of the prop barrel and the thing expired. Seems to me that the original OMC answer did add some drag to the slipstream that the Merc design (which is all I see anymore unless the barrel is just straight and longer) didn't.

Mark

 

[phillnjack2]

Re: Propeller convergence ring removal

I think the flare has become the norm on short hubs, and like said above just a longer barrel on others.

i cannot see the ring doing much good at high speed, but probably very good at under planing speeds.
i have a flared end on a suzuki prop and another prop on the suzuki with no flare,both seem ok to me.

maybe it was just meant for the slow cruiser boats, but the sst teflon prop was meant for high speed.
In its day this was the top racing prop for fast offshore speedboats.



phill