Thru Hub Exhaust - Flaired End

[Rapid Racer]

Can anyone tell me the purpose of the faired end on a thru hub exhaust? We use Standard 3 blade, 9 1/4" x 11"P aluminium props on a 9.9 hp and cut them up. We also jack the outboard up once underway, to get the shaft centreline approx 1" above the bottom of the boat. We are thinking of cutting off the flair end but want some opinions before hacking into a good prop.

Thanks
Daniel

[Rapid Racer]

It's OK, I now know what it's for.

[Ron Hill]

Don't cut it is my advice! But what have you been told?

[Rapid Racer]

Don't cut it is my advice! But what have you been told?


Ive been told it's to keep the exhaust gasses away from the prop on take-off. Further i've been told some people cut (machine) them off, but there is no noticeable difference. So just leave them.

[Ron Hill]

A real expert might not agree with me, but what I figured out by cutting the rings off was, A. The boats were harder to plane and B. No net gain in speed....aluminum props mind you...

I thought that the flare forced the water out on the blade to make it "HOOK UP" or "BITE"....without the flare the water just roll off the blade and "BLOWS OUT" or "Cavitates"....Or as Dan Schwarzenbach used to say, "Calvokate." Lords know you don't want to "Calvokate".....especially in rough water...

OMC used a reverse flair until Merc's patent ran out...The original patent may have been by Dick Snyder at Mercury.

[JohnsonM50]

While we're all hearin things :rolleyes: Ive heard that if you cut/remove the diffuser & extent the exit hole with a tube a couple inches itll also be about the same [or small gain], havnt actually done it & think it would be hard to document a real difference. I do think stuff like that is worth tryin for the fun of it but with an insignificant prop at 1st.

[Rapid Racer]

A real expert might not agree with me, but what I figured out by cutting the rings off was, A. The boats were harder to plane and B. No net gain in speed....aluminum props mind you...

I thought that the flare forced the water out on the blade to make it "HOOK UP" or "BITE"....without the flare the water just roll off the blade and "BLOWS OUT" or "Cavitates"....Or as Dan Schwarzenbach used to say, "Calvokate." Lords know you don't want to "Calvokate".....especially in rough water...

OMC used a reverse flair until Merc's patent ran out...The original patent may have been by Dick Snyder at Mercury.


Well what we don't need is to make it harder to get on the plane or "Calvokate". We have enough trouble with both of them as it is!

[Powerabout]

It also helps with accelerating in slow corners, like trick skiing or wake boarding.
It stops the gas from getting around to the front of the blades.
BTDT remove either a diverging or converging cone and the prop lets go much easier on accelerating turns when climbing on the plane or slow turns.

Thats why stock props have them and race ones dont.

[fs5]

i've ran a couple of the older omc 55hp props on my merc's,and first thing i did was rip that defuser ring thing off .they plained off great and excellerated great and held on well through tight turns.
ran these props on numerous tinnys and tcats on my 40 4cyl merc and 3 cyl 55hp seapro,
maybe it was the larger diameter that kept them holding on???

i wouldn't chop one off a alloy merc prop though or you'l never get it to plain,unless you belt some more cup into it.

[palhal]

Cut the flare off. I have been doing it for years on all the hi-speed Bass Boats. It picks up a couple miles an hour. A lot of the new props don't have the flare. Why put up with the flared drag in the water not to mention rotating weight.

[JohnsonM50]

Cut the flare off. I have been doing it for years on all the hi-speed Bass Boats. It picks up a couple miles an hour. A lot of the new props don't have the flare. Why put up with the flared drag in the water not to mention rotating weight.
That might work with the actual flaired props but the diffuser ring OMC types are best left alone unless you want to experiment with an extension pipe of a couple inches. If rotating weight made a big difference we'd all be using comp-props :eek::D:D:D

[Rapid Racer]

What we ended up with was some (not all) of the rings removed from one prop guy and the others left on by another. With no real way of testing them we don't know any before-after differance. The ones from the second guy were the fastest easily, but we smashed them both pretty good.