Two Blade Prop for Alpha 1?

[Formula Jr]

Please don't slam the question - I have reasons.......

Having gone thru a rather exhaustive search with no results, I figure this is the only place left to ask.

Does anyone know of a suppler for two bladed speed props (raked) that would fit a standard Alpha/Type 1-MR, or is this just NA. I suppose I could just get a four blade and cut and balance the prop but that would be extreme. Also, has anyone seen a rear cone to smooth out the flow behind a Merc Alpha Prop: Something that would replace the regular diffuser ring.

Thanks in advance..

[Moody Blu']

your always lookin for that extra mph?
arent ya :D

[BigGrizzly]

burt a two blade is tough. years ago the found that well designed three blades added speed on outboards and outdrives. The old racing two blades were bronze and weighted on one blade. If speed is what you want without the defuser ring get a over the hub chopper style prop. try powertech or Hill. This is what my Corsican has--over the hub. There is no exhaust hole in the middle. for exhaust

Randy

[Formula Jr]

I'm just thinking out loud here Big Grizzly. A two blade is the most efficent "balanced" design - a one blade being the most efficent for a non-surface piercing design. If it was Stainless - and it hasn't been too long that cutting machines could work Stainless (20 years or so), then the flexing problem would have been solved by the added rigidity of the material. But yet no prop maker took up two blade designs in SS for thru hub exhaust props. I gotta wonder if this is just a blind spot, or as you say - they've been there, done that. I'll look up those makers you mentioned.
The relevant sites:
http://www.chadhillpropellers.com/
http://www.ptprop.com/
http://www.propswap.com/
The prop swap looks interesting. If only they listed Below Retail.....
:mad:

[Jamesbon]

Formula Jr,
Hmmmm, a thought provoking question. Although I have no relevant info. pertaining to your question, I can offer only what I've noticed over the years.

I've noticed 2 blade props usually only on unlimited hydroplanes, v-drive type flat bottoms and small drag boats, all of which are "inboards." Maybe there's a correlation?

Why are 2 blades usually mounted on those types of boats?

Nate

[Formula Jr]

cause they spin them to horrific RPMs with something like 15 to 17 inch pitches. You'll note that all the drag hydros have cleavers and the flat bottoms choppers.

[Formula Jr]

Sky, yep! always looken for easy stuff.

[Looped]

Here is a little prop tid-bit info:
http://www.scaryfast.com/prop.htm

Craig

[Forrest]

One problem that two-blade props have on outboards and sterndrives is that for every rotation of the prop, both blades will be exactly lined up with the drive housing and the skeg at the same time. This creates a vibration condition even though the prop is perfectly balanced. On a three blade or five-blade prop, only one blade is in line with the housing or skeg at any one time while the other blades are in "clean" unobstructed water. On the other hand, a four blade prop does get two of it blades lined up the with the housing and the skeg a the same time, but apparently, the other two blades that are in unobstructed water tend to cancel any vibrations caused by the other two blades.

[Formula Jr]

Like what ya said there Forrest. Obviously I need to think alittle more about this. My gut tells me there's 3 to 5 MPH in there somewhere. When I got the boat the diffuser ring was taken off. I ribbed the brother about this and he just said its faster that way. When I replaced the prop with a rebuild with the ring, I lost about 1 MPH. I've got thru hull only exhaust so the ring is really just a drag. I've never seen anyone address what you do with an old thru hub exhaust prop once you run exhaust thru the transom. I'm thinking there would be some MPH gains if you put a cone over the back of the prop to cleanup the water flow. Something light, like aluminum with three screws holding it on the old diffuser ring indentation. I just gotta try the experiment.

[Looped]

There’s nothing like a good prop with stern lift, right Scott! :rolleyes:

Craig

[Formula Jr]

http://www.epud.net/~owen/freshprop1.jpg
http://www.epud.net/~owen/freshprop2.jpg
http://www.epud.net/~owen/freshprop3.jpg