OMC prop plastic guard

[thatone123]

My question is specific to the classic 2 stroke 9,9/15 but could also relate to many OMC props. Over the years I remember talk about this but is seems foggy and there were more than 1 opinion. Question is : Is the plastic gizmo - guard or whatever it is called on the back of the prop necessary? I think I read on time it effected prop backwash affecting exhaust? Answers would be appreciated. I have run without these before without any discernable difference in performance.

 

[racerone]

I believe it was called a ----" converging ring "--------A big word for me .----Might look it up in a dictionary.

 

[F_R]

It is supposed to keep exhaust gasses out of the prop (prevent cavitation). Interestingly, Mercury had it first, but they flared theirs outward. Marketing, patents, or propaganda, or whatever, OMC flared theirs inward. Supposed to converge the water back in behind the prop and increase speed and performance. Lots of people knocked them off and turned them around like Merc. Others just left them off. I guess in the long run Merc won the debate.

 

[jimmbo]

By the mid 90s, OMC was mounting the ring to flare outward. On the V6 props.

 

[racerone]

I picked up a ---" little stainless raker "-- for a V-4 and the hub is straight.----No flare and no converging ring.

 

[interalian]

I got a new BRP prop for my 140 and it just has a flare toward the back of the exhaust outlet, no ring.

 

[jimmbo]

The RAKER has always been a straight tube.

 

[thatone123]

So I guess are you guys saying that it really does not matter? That seems to be the case as I see it and I happen to have a prop with the guard missing, so I guess I will use it "as is". Will I lose any performance etc. ?

 

[thatone123]

Who knows, maybe it will catch less weeds.

 

[F_R]

So I guess are you guys saying that it really does not matter? That seems to be the case as I see it and I happen to have a prop with the guard missing, so I guess I will use it "as is". Will I lose any performance etc. ?

Might even go faster with less drag. Somebody mentioned that some performance props do not have a ring. Bottom line is if you are not experiencing cavitation, and are happy with it, run it and don't give it a second thought.

 

[thatone123]

I ran it today 10 miles and it did slip or I guess cavitate at high speed and on curves. I will try the same standard 9/11 prop with the guard and see what happens soon. Actually the best performance all around seems to be a 10 inch 2 blade. Does this make sense?

 

[F_R]

9 x 11 is probably too much prop for it. The 10 inch makes sense to me. Especially if it is a 15hp. They need to rev up to get 15hp out of them. Of course, it all boils down to the boat and load.

 

[thatone123]

Today I used the standard 9/11 and it only lost bite a little on sharp corners. Those guards must give the prop more bite for sure. The boat has been loaded light and it is high up with the prop just at the bottom of the transom. I used a 9/12 last year with good results, except it lost some bite at high acceleration to get on plane. I am in shallow water all the time and need to get on step in one boat length to get propelled immediately so as not to drag the bottom and keep me from getting on plane. On a 12 ft Jon boat the 15 will do it.

 

[jimmbo]

There many reasons a prop can lose its bite on the water, or fail to get a good one in the first place, there is probaly more to this than just the Converging Ring. Comparisons with the 9 1/2 is an Apples to Oranges comparision. Totally different gear cases, props and exhaust discharge, as well as a completely different engine