Diffuser Rings - what do they do?
 

I have two sets of props, Hydro Quad IV's without rings, and P5X's with the diffuser rings. The Quad IV's perform great. I'm getting ready to have the 5-blades tweeked some, and I'm wondering if I should keep the rings.

What do these things do?

Brian

Re: Diffuser Rings - what do they do?
 

Among other things...They help prevent the exhaust gases(only on a thru-hub exhaust system) from migrating forward into the slipstream(the flow of water passing over the lower-unit & propeller hub), which causes cavitation(mostly at planing speeds) & in worst cases, complete blow-out(total loss of propeller "grip"). Some twin engine performance sterndrive installations, with "thru-hull" exhaust benefit from propellers without diffuser rings, others do not. Alot of variables come into play on a given hull design & rigging, such as toe-in, toe-out, hull strake placement & size, X-demension, drive hydrodynamics(shape), step type, size, placement, etc... The bottom line is...It comes down to a working hypothesis(educated guess) & some trial & error prop testing. Been there...many times. Ed

Re: Diffuser Rings - what do they do?
 

Hello Brian,

I hope all is well! The diffuser ring on the Hydro P5-X is very minimal. In your case you could certainly remove it and I don't think it will negatively affect your planning. However I don't think that there is much to gained from removing the ring on the P5-X propeller, beceause it is so small to begin with. Typically with a full ring removal, like that performed to a Mercury Bravo I can be good for 3/4 MPH increase. In some cases additionally you may experience a decrease in stern lift, but this is typically noted on boats with high X-Dimensions. So that being said I don't believe that this will be the case with your boat. Hope this helps.

Julie

PS: See you in Sarasota!

Re: Diffuser Rings - what do they do?
 

Some boat manufacturers have us remove the rings right away. Most don't. If the propeller is surface piercing, it can reduce stern lift by cutting it off.

Re: Diffuser Rings - what do they do?
 

Thanks Ed - my Konrad drives don't exhaust thru the prop, they dump in front of the upper. Most (all) of the time, I'm running straight out the exhaust tips well above the water line, so there's one argument for removing them. My lowers also have nosecone leading edges, and my x-dim has the propshafts at about 5" below the running surfaces.

Brent, not surface piercing, it's a P5X with slightly raised X.

Julie, I shipped these to you today. They need to be looked at with your fancy scan machine, and adjust some things. I'm guessing you'll find the R prop is slightly lower in pitch, as I'm seeing the right side at +200 rpm from the left. The Quad 4's are dead even.

Please call me when they arrive. I've juiced up power over the winter, so we need to tweek some things other than the diffuser rings.

Thanks!
Brian

Re: Diffuser Rings - what do they do?
 

Sounds great Brian! Thank you. I will call you after we perform some diagnostics.

Julie

Re: Diffuser Rings - what do they do?
 

With the rings cut off will a boat be harder to get up on plane with the same pitch prop ?

L.S.

Re: Diffuser Rings - what do they do?
 

So no answers ???????????

L.S.

Re: Diffuser Rings - what do they do?
 

LS, not sure I can give you an answer, but in my situation with 5-blade props, getting up on plane isn't an issue.

Mine are coming off.

Brian

Re: Diffuser Rings - what do they do?
 

So did you try a set with the rings cut off? We have 4 blade props.

Re: Diffuser Rings - what do they do?
 

The first thing I do to my props is cut the ring off. I haven't seen any negative affects from removing it as far as time to plane or midrange speeds. I do see an extra 3 mph on the top end.
I run Merc Labbed B1 props on a 41 Velocity

Re: Diffuser Rings - what do they do?
 

Well thanks all for your imput.......tomorrow we are testing a set of 34 "s
without the ring...... if I can pick up 3 mph I'll be thrilled......let ya all know.

L.S.

Re: Diffuser Rings - what do they do?
 

p4-33...Just noticed you are from "Downriver"/Gibraltar. Does Hedke still own the Gibraltar Boat Yard? My dad built that marina from swamp in the mid-50's & sold it in the late sixties, to move to Florida. Back then, it was called "Humbug Marina". Ed

Re: Diffuser Rings - what do they do?
 

Yes, Mr Hedke, along with his 5 sons and umteen grandkids still own and run Humbug Marina. Mr Hedke and one of his sons's are neighbors right across the street from me. Don't know how big if was back then, but today they have 700 or so slips, plus room for 300+ in a rack storage building.

Nice family, class operation. What's your dad's name? I'll say "hi" for ya.

Cheers,
Brian

Re: Diffuser Rings - what do they do?
 

Matt & Julie have them now, doing some tweeking. I'll have them for the Sarasota race this weekend.

Brian

Re: Diffuser Rings - what do they do?
 

how much would taking the ring out hurt bottom end?
heard 2 different sides

Re: Diffuser Rings - what do they do?
 

Lucky Strike did you ever get the chance to test out the props with and without tthe diffuser ring? If so what were the performance #'s? Thanks

Re: Diffuser Rings - what do they do?
 

mwdill,

With through transom exhaust it should affect low end planing little to none.

Re: Diffuser Rings - what do they do?
 

thank's :D:

Re: Diffuser Rings - what do they do?
 

No---it was to rough in the ocean to test.
Where I live you can only go 25 mph in the ICW.

L.S.

Re: Diffuser Rings - what do they do?
 

Since no one posted their results here, I assume there was no noticeable difference in top speed?
John B

Re: Diffuser Rings - what do they do?
 

Seeing that this was my thread...

After some significant power plant changes last Winter (04/05), we found that my P5-X's were not going to be enough prop, even after adding the maximum pitch we could safely get away with. I ended up selling the P5-X's as-factory, with the diffuser rings still attached.

I also went in search of a different set of props, with no rings.

Anyone else?

Brian