Prop question

[specboatops]

On some of the 4 bladed props the tube is either straight or flared and the back, what is the difference and what different applications are these for ?

[Dave Strong]

Always wondered that myself, thought it had something to do with exhaust flow? Someone will know.

Dave

[transomstand]

Depends on the "needs" of the prop design. Some blade designs will actually pull the exhaust back over the blades so they make the exhaust tube longer. Some also use the flared diffuser ring to help pull exhaust from the gearcase housing.

I think it's one of those prop guy voodoo things that none of us mortals will ever figure out:D

[Dave Strong]

OMC had some crazy flares on some of their aluminum props.

Dave

[FUJIMO]

Paging Vortex Artision!...Paging Vortex Artesion!...lol

[Onetime]

I was told by the late Dave Bostic, founder of Hoss propellers, the flare on the tail of the through hub was to help with planning and create some tail lift.

[specboatops]

Keep the answers coming, when I first purchased my boat it had a flared 4 blade thru hub prop, no identifying marks on it, ran great, but eventually threw a blade, I hastily through it in the garbage and put on one of my other props. Thinking back, it was one of the best running props ( for my heavy boat) and I have no clue what it even was, just remember the flare at the exhaust end, always wondered what exactly that does for a certain set up, what type of boats can benefit from it, what boats is it not for type of thing....

[whipper]

In theory the defuser ring is supost to stop gasses from making there way back to the blades that leave the hub buy creating a pressure difference. Haven't been able to watch this happen and not sure if it would work on surfacing applications at speed. Maybe at 40 or 50? Maybe these props would have stopped the water from being ingested in the older XS at speed? kinda like a spoiler on a car.

[Dave Strong]

Keep the answers coming, when I first purchased my boat it had a flared 4 blade thru hub prop, no identifying marks on it, ran great, but eventually threw a blade, I hastily through it in the garbage and put on one of my other props. Thinking back, it was one of the best running props ( for my heavy boat) and I have no clue what it even was, just remember the flare at the exhaust end, always wondered what exactly that does for a certain set up, what type of boats can benefit from it, what boats is it not for type of thing....


OMC? know what pitch and dia.? Have a few at work been there for years. Maybe the boss will sell you one.

Dave

[eli]

there was a ring I installed on several props called blowout ring was on rear of hub ,maybe helps with steering torque and slowing down surely is not for top speed

[specboatops]

OMC? know what pitch and dia.? Have a few at work been there for years. Maybe the boss will sell you one.

Dave

No it's a Merc, I think Mach makes some of these, was just curious why the flare at the back of the barrel ?

[Mr. Demeanor]

The flare and length of tube effects lift. Flare and/or longer tube creates a prop with less bow lift and planes quicker or holds larger boats on plane at slower speeds.

[specboatops]

The flare and length of tube effects lift. Flare and/or longer tube creates a prop with less bow lift and planes quicker or holds larger boats on plane at slower speeds.

So if I understand you correctly IF I want bow lift, I would NOT want a prop with the flare at the tail end of it ?

[PropHydro]

A flare ring or diffuser does two things. First it aids in hole shot by drawing water back into the blades to help with excess cavitation. Second it does add tail lift to the boat. The question is understanding each individual application, and what will work for which boat. For example a flare ring might help with hole shot but limit the bow lift, and possibly scrub off speed. Adversely if you were to remove flare ring you might get bow lift and speed back but kill the hole shot with excess cavitation... It is a fine line...

[specboatops]

But this is not a ring, it is built into the design of the prop is what I am stating ( unless what you are trying to say is that part can be removed/ ground off) when you look at some of the 4 bladed props at the rear of the tube/ hub, the very aft section has a flare to it ( I hope I'm explaining this correctly) when I first bought my boat this is what it had, I threw a blade and then purchased a few trophy's, a Mazco HP-4, and a Fury, looking back, that prop with the flare seemed to really run the boat well, I'm just curious what you all think of them, ( my boat is a Gambler SuperSport) and IF that type of prop would be beneficial to me ? I just never understood what the real difference was, bored this winter made me ask myself the question I guess.....

[PropHydro]

The flare ring can be cast into prop or added on, we do both. On your boat I could see why that worked for you because the Gambler likes a certain amount of tail lift. The Gambler has a lot of weight in the rear that is why it likes that style. Feel free to call with any specifics on set up. 330-425-3629.

Todd

[Hoss Marine Propellers]

As stated by others, The flare on the back of the hub is used to create a higher water pressure at that particular spot and stop the exhaust from wrapping back around and being sucked into the low pressure area of the blades.One of the side effects is increased tail lift/ reduced bow lift from the flare. A straight barrel has to be longer thus creating a longer path for the exhaust to travel.We did extensive testing with the flare on our Triton 2 thru-hub back in the mid '80s. You don't want the flare too big because that's drag. The most radical test was removing the flair all together...... about 40 mph or so, the prop would loose ALL bite and rev up..... would stay in that condition as the boat slowed and came off plane... you would almost have to come to a complete stop before it would bite again! There was nothing we could do to get it to stay hooked up until we welded a new ring back on.One issue that effects flare vs straight is the amount of torque at the steering wheel do to blade design. Lots of torque means that the gearcase is actually "crabbing" sideways thru the water..... a flare would work better than straight....... straight works better with a prop with minimal torque.Another issue is surfacing the gearcase/prop with low water pickups. Now you end up in a whole different scenario?

[Carter Powell]

Years ago I knew a man who worked for Mercury back in the 60s and he claimed that the flair on the end of the props helped evacuate the exhaust gases on a totaly submerged lower unit. It helped create a vacuum effect.

Carter Powell

[Hoss Marine Propellers]

Years ago I knew a man who worked for Mercury back in the 60s and he claimed that the flair on the end of the props helped evacuate the exhaust gases on a totaly submerged lower unit. It helped create a vacuum effect.

Carter Powell

Yes, i believe this to be true for smaller HP engines running fully submerged.

One of the first things we did on the OMC V4 SST prop was pop the brass/bronze ring off the back of the prop and turn it around creating the flare effect.