p4-33

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

Ed

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

throttleup

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!

bbladesprops

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.

p4-33

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

throttleup

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

Julie

lucky strike

iTrader: (1)

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

L.S.

lucky strike

iTrader: (1)

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

L.S.

p4-33

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

lucky strike

iTrader: (1)

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