Different props for Alpha vs. Bravo????
 

Been doing lots of reading here and looking at used props, but not finding much on what is the difference between props meant for a Alpha drive and a Bravo drive? also, how would you tell when shopping for a new prop or used prop?

Things I think I have read or implied:
Bravo gear case is bigger than an alph, so is the prop hub different diameter?

Rubber Vs. solid core? solid core is for higher HP and would not apply to alpha's?

Bravo props may put too much torque on a alpha and break it? Is this due to the bravo prop has a larger diameter and/or more blade area for the same pitch? what about if it is a stock 350 - 260HP in front of the alpha vs. a BBC?

As above, a four blade prop on an alpha will also put too much torque on it causing wear? Is this only if the motor will produce too much torque?

If shopping for props for a twin SBC Alpha application, what do you look for if you know what pitch you want to try? Splines, diameter vs. pitch, blades, alpha vs. bravo??

this stuff is confusing and I went into it knowing it was confusing!

Brian

More Reading
 

Read about different props for different drives and all the applications. Your post will require a lot explaining, this should help with most of your questions.


http://www.mercurymarine.com/propellers/

http://www.mercuryracing.com/propellers/

The Alpha and B1 has the same size hub/barrel and run the same props. The big difference is, that a boat with an Alpha will usually require one type of prop, where a B1 boat another. It boils down to the fact that the Alpha boats are normally smaller with less power and slower. If you run a Maximus or B1 prop on your Alpha there is a good chance you'll tear it apart. It is build for smaller diameter props that put less load on the drive compared to the Bravo 1. Regarding the rubber hub and the solid hub is a question about power and strength. Merc reccomends the impact absorbant rubber hub up to 380 hp and the solid hub for 400+ hp. There is also the XR 1.1/4" hub, and that will only fit XR size driveshafts.

Here is a list of the most commom uses of the different merc props. The order is random.

The props normally used on Alpha's are:
LaserII
Mirage+
Vensura
Revolution4
High Five
You can run the Maximus (15.25 or less dia.) and Bravo1 prop, but it is rare that an Alpha boat calls for this, and it can hurt the drive.

The props normally used on the Bravo 1, Bravo 1X, Bravo 1XR:
Mirage+
Revolution4
Bravo1
Maximus
Hydromotives, Herings ect.
You will of course see Bravo boats run some of the others as well, but these are the most common in high performance boating.

What make/model boat are you getting props for?

This is the info needed, for the best advice possible.

Engine Make/Model/HP/Top end min-max rpm's?
Current engine RPM @ top GPS speed?
Current prop. Make/Model/Pitch/Diameter?
Drive gear ratio?
If possible, prop depth. The prop shaft centerline distance measured perpendicular to the bottom directly in front of the drive, with drive trimmed to neutral ie. same angle as bottom directly in front of the drive?

Thank you
 

Thank you for the info and the links, more reading to do.

I did find elsewhere that both are 15 spline and the rubber hub would be recommended. max dia. on the Alpha is 15", but people have posted about fitting about 15.75 before running into the cav plate.

I am looking at a formula 272LS w/ alpha's and 260HP - 350's, so in the 21 to 23 pitch area.

Brian

I'f you'd like to call us, I can cover a lot of ground with you in short order.
No questions are silly and we love to educate folks.
Let us know if we can help.

Brett

I run 23 Revo 4's on CR alpha drives on a 26 Sutphen. I think it's balanced perfectly. You could be very happy with Revo 21's if you are also CR. I wouldn't know where to begin on same rotation drives.

Old post, but thought I would update it. Been a long project detailed on on my build thread in the formula section, but I ended up doing lots of work to the boat and repowering with vortec 350's. Running alpha 1 drives at 1.5:1 ratio. for first testing, I put some solas 4 blade aluminum 21p props on it for tubing with the family. The bow really likes to rise up when planing and unless you tuck the drives all the way in you are not getting up on plane, just looking skyward. With the tabs down and drives tucked, she pushes up on plane fairly level. When running, the boat runs about perfect with the drives neutral, just a slight bounce with some waves. If you go up a degree or two on the drives, the bow comes up and gets light. Not bad, but she will porpoise with any more trim. Engines finally run well, but only run up to 4200 rpm as I do not have the timing set right. They hit about 3200 with the primaries on the quadrajets and then only 1000 more. From about 2/3 throttle and up, makes no more power so definately think timing is too low (set that way to be conservative)

Recently a tried a set of 23 pitch Laser II and it really changed. No tabs, drives neutral and it just pushed up on plane. Problem is the bow will not come up, it steers around the bow and the stern feels floaty. Not good at all. RPMs are still about 4100 or so, so timing problem is consistent. We will reset the timing this week and try it again. But the laser II just do not have enough bow lift for this boat, It was trimmed almost all the way out to where the limit switches would stop it also. Had maybe a couple degrees left and nothing. Gotta admit, it planed really easy, just rode terrible and felt dangerous.

so now I am looking at 23 pitch Mirage props to try or 21p mirage plus. We will see how it goes then.

Just wanted to post a recap since I started this thread and never put my findings here. Heavy boat like a deep vee formula, stay away from the laser II's. I will have to check my X-dimension and add it here for others also, should be pretty standard with a 86 formula 272 with standard alpha's.

Brian

What do you have timing set to at full advance??? Running too little timing causes high EGT's and is bad for the engine. You should be around 28-30* total with vortec heads.

We had originally set the engines at 10 degrees idle and 28 to 30 at 3k which should be good. But we have messed around with timing a bit while dialing them in and I am not positive where it is set now, so need to put the light on them and check. The JEGS timing tape on my port motor came off the balancer and I just got the new one in. Makes reading the timing a whole lot easier and more accurate.

Brian

I Think you are running too much prop. try 19p

Well, figure I should update this thread. Went out with my 2 boys and took the timing light with us a couple weeks back. Turns out the engines were too far advanced! I was afraid I had toasted the engines due to detonation as on startup while setting the timing, the port motor had a little "rattle" too it until it fired. I set the timing on both at 10 degrees base and ran it again. Still would not pull above 4100 rpm with the 4 blade -21p Solas aluminum props. But I did get a gps speed of 47 mph max which is 14% slip. Idling back in, the port motor again seemed to have a noise in it.

Well, we pulled both engiens out this week and this is what we found. Both had loose rocker arms. This has happened before, so all the rocker arm nuts are junk. No wonder it wouldn't make power, it was running on 4 or 5 cylinders on each engine. The cylinders and plugs all look good if a bit heavy on carbon for 11 hours of running. But being rich and running the 93 octane in an engine designed for 87 is probably what saved it with the excess timing I was running. Well, that and almost all my time was at 3100 rpms or less with no real long runs on it. Got lucky and will not make that mistake again.

Oh, minimum planning speed turned out to be about 16mph. 1/3 fuel, 3 people. Bennet tabs down and drives tucked in, handled real nice at that speed. Any slower and around 14 mph it would want to fall off plane if you turned. 16mph is pretty dang slow for tubing, most want to be in the 22 to 28 range for my kids.

Next summer I will be running 23p mirage props, counter rotating. Putting a CR lower on it and with the motors out, will be increasing the cam a bit and doing some head work to the vortecs (valves, springs, roller lifters).

Motor detail will be in my thread in the formula section soon.

I spin 21 3 blades. Believe it's stiletto up to 4700 and 58-60 mph on avg. seen a best of 63

What was your setup? If I remember, you still had small blocks? Best of 63 I would guess slightly modified. If that is the case, better cam mine for more hp.

my 27 nova 3 likes 23 mirages. i think i am closer to 325 hp each though, and a hair lighter than the formula...

Well, with what I am putting back in, I am shooting for 350 hp or more each.

Basic L31 vortec engine with a XM-270-HR cam through 1.5 roller rockers. Aluminum intake and stock quadrajet carbs. CR alpha drives. Should push the 23p mirage props and lift the bow is my hope. Speed? I just hope the dang thing runs all summer and will hit 60. I suspect mid 60's, but will take anything under it's own power and over 50 at this point.

prev owner who did motors said he saw 63 gps. the nova 3 has a step and a small pad, but i don't think they helped top speed any. so 60-ish should be in the ballpark. i don't run it that hard. spousal unit starts complaining at 40, and by the time i am over 55, she is making more noise than the engines...

Sometimes spousal units get out of calibration. This can happen if to much lube is applied. It allows them to spin up without the needed friction coefficient. When this happens it allows them to easily over rev and the calibration goes out of whack. When this happens plugging the rear exhaust port with a thrusting tool fixes the problem. If it doesn't, you may have to either smack the unit with a deadblow hammer or simply replace the unit all together,

If you opt to replace the unit, several reviews have stated the it can be confusing telling the difference between the spousal unit and the new improved boathoe units as the part numbers are very similar. The differences are usually well apparent if you are not distracted by packaging "bling" . While both units can look nearly identical, upon activation the spousal unit will make low grumbling noises such as "STOP: "NO" and "SLOWDOWN" while the boat how unit will make louder higher pitched squeals such as "HARDER" "FASTER" and "YESSS!!!"

lmao !!

I have a 270 laser stock 350 mags with alpha drive 1.5 with one counter rotation. And my boat runs 64 with 25p ss hull brand and my boat turns 4500 rpms