Largest Prop for an Alpha I?

[kdmiller8251]

Whats the largest diameter prop a person can run on an alpha I? I have a with a 350 and was curious.. Currently running a 14 x 20p prop...<br /><br />Thanks<br /><br />Kdmiller

 

[jdcook]

Re: Largest Prop for an Alpha I?

My alpha1 has a 14" prop as well, I don't think a bigger prop would fit on my setup.......Maybe a 14 1/2.

 

[flashback]

Re: Largest Prop for an Alpha I?

I have a pre alpha on a 21 ft chris craft and I believe the prop is 15.5 x 19p...

 

[Doug Durako]

Re: Largest Prop for an Alpha I?

Hey, Tallman------I've got a Merc/Quicksilver you can test if you'd like. We are experimenting with a torque/shift prop right now and you can borrow the one listed below for a weekend if you want to try it. Let me know---I live just a few miles outside of Bloomington. Do you still have my email address?-----Doug

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

Doug:<br /><br />Thanks, still got your email add. No thanks, I have a quicksilver Stainless 21p in the garage. Not sure what the diameter is at present. Just kind of curious as to how big I can go, and if I am getting the most out of what I have on my current setup which is a Vortex 4 blade 14x21p.<br /><br />I have seen those torque shift ones, let me know how it works out..<br /><br />Thanks<br /><br />Kelvin

 

[Doug Durako]

Re: Largest Prop for an Alpha I?

Kelvin---I'll measure the diameter on the torque shift cause I am pretty sure it is close to 15 inches at the low 13 pitch setting.<br /><br />So far, without tuning, the prop gets my rig completely on plane and running about 30 in about 3.5 seconds---pretty much throws you back in the seat.<br /><br />Top end is about the same as before, so I am taking the prop apart and starting over with settings to spec.<br /><br />Well pleased so far----Doug

 

[Doug Durako]

Re: Largest Prop for an Alpha I?

Kelvin---the torque shift runs about 14 inches in diameter. I still have some clearance on the Alpha unit, but I don't think it would turn a much bigger prop. I am only getting slightly above 4000 rmp right now at WOT on the torque shift so I need to dial the top pitch setting down to about 22 or 23 pitch (it shifts from 13 pitch to 26 max pitch right now).---Doug

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

Doug:<br /><br />What Rpm range you shooting for on???<br /><br />Currently with my prop I think its a 19 or 20 I am running 4200 WOT...<br /><br />K

 

[kopy kat]

Re: Largest Prop for an Alpha I?

Tallman--I have just removed a Bravo One prop that was 15.5 x 17---the large diameter caused over heating due to our altitude (6,220 ft)--you have to have the "flat" anode on your upper plate, otherwise the larger diameter prop will hit the "skeg" on some of the anodes.

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

Yeah I have the flat anode, are the Alpha and Bravo sizes the same???<br /><br />Tallman

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

bump

 

[Bondo]

Re: Largest Prop for an Alpha I?

I Believe you can swing 16" on any Mercruiser prop shaft before you'll encounter any contact with the housing......<br /><br />As I've said before, The Diameter is Totally Irrelevant to the end-user....<br />You Should be looking at Pitch,+ Blade design.....<br />The Dia. is determined by the engineer who designed the prop.. Low pitches Need bigger dia.s... Cleavers, Choppers, 3 blades, 4 blades, 5 blades....<br />If you walked into the biggest Prop Shop in the land,+ Wanted a prop of a given blade design,+ pitch... Then told them you wanted it in 1" smaller or larger size.... They'd Laugh you out of the parkinglot...

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

Bondo:<br /><br />Thanks for the heads up, That makes sense never really looked at it that way....<br /><br />Tallman

 

[kopy kat]

Re: Largest Prop for an Alpha I?

one last comment--a 2" pitch reduction will equal about a 200 rpm increase---as will a 1" reduction in the diameter of the prop equal at least a 100 rpm increase--been there-learned from it--hit the rev limiter-now changing to a new prop. It helps to buy from a dealer that is willing to let you try props, and exchange them if they're not right.<br />

 

[Doug Durako]

Re: Largest Prop for an Alpha I?

So, bondo---what's the difference between Tallman's 21 pitch prop and mine---his gets 4200 rpm and mine gets 4800----are you saying all the performance difference is in the cupping on the blade?<br /><br />I know boat design also plays a part, but I would think with the same engine and drive he should get close to the same rpm as mine.

 

[MrBill]

Re: Largest Prop for an Alpha I?

The original question regarding largest prop diameter on an Alpha 1 needs to include the Generation of Alpha 1 being discussed the Gen 1 and 2 vary slightly, with the Gen 2 capable of utilizing a slightly larger diameter prop.<br /><br />Regarding some of the other discussion about customer props, etc. There are a huge number of custom prop shops nationwide along the coasts, the call for custom prop applications tends to be in far more demand in salt water applications. Custom props for 18-24 foot craft tend to run 15 to 40% more than off-the-shelf items...and I don't know anyone who's been laughed out of the lot, only those who have run out of the lot holding on to their wallets.

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

Sooooo.. I guess my other question is should I be getting more RPM out of my current set up or is this normal???<br /><br />Tallman

 

[kdmiller8251]

Re: Largest Prop for an Alpha I?

I have I would assume a GEN I....<br />SN# OC 812776<br /><br />Is not called a Gen II I know for sure<br /><br />Tallman

 

[Bondo]

Re: Largest Prop for an Alpha I?

Kelvin,<br />You May want to try another prop... You Are at the lower end of the recommended WOT rpm range of a 350....<br />ddboater,<br />There are a Zillion different blade designs, cups, dia.s, etc. out there... It's Blade Design... Not Boat design that I'm talking about....<br />Two 21" props that look alot alike, made by two companies will behave Very Differently..... In more ways than just different rpms....<br />MrBill,<br />I agree that Custom props are the way to go.... I'm just pointing out that Blade Design is Much more Important, Than Diameter, to the End-user.....<br /><br />I've got the Torque-Shift.... I Love It.....

 

[Bondo]

Re: Largest Prop for an Alpha I?

I went out today,+ Measured......<br />A Mod.1<br />An Alpha1<br />+ An Alpha1 GenII<br />They are All 8 1/4" from the center of the propshaft to the housing.....