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Old 08-19-2012, 01:28 PM
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Hi guys, have an 87' 211 Liberator running a 454 Alpha one set up, and am currently running a 15.3 by 19P stainless quicksilver prop. It runs at about 48mph WOT at about 4400rpm.

Well the other day you I dinged the prop and thought it a good idea to buy a back up. So I bought an alloy prop that was recommended to me by the local marine, this was a 14.4 by 21P. I took the boat out today and at WOT achieved 2600 rpm and about 12 mph!!!

What gives?? Do you guys have any idea what is going on? What sort of prop would you think I should be running?
I would like to see 55-60 mph at 5000WOT.

Advice here in the UK is shocking, so I really hope you guys can help.

Thanks in advance.
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Old 08-19-2012, 02:18 PM
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Originally Posted by strega View Post
Hi guys, have an 87' 211 Liberator running a 454 Alpha one set up, and am currently running a 15.3 by 19P stainless quicksilver prop. It runs at about 48mph WOT at about 4400rpm.

Well the other day you I dinged the prop and thought it a good idea to buy a back up. So I bought an alloy prop that was recommended to me by the local marine, this was a 14.4 by 21P. I took the boat out today and at WOT achieved 2600 rpm and about 12 mph!!!

What gives?? Do you guys have any idea what is going on? What sort of prop would you think I should be running?
I would like to see 55-60 mph at 5000WOT.

Advice here in the UK is shocking, so I really hope you guys can help.

Thanks in advance.
sell what you have and find another faster hull...i have a customer that sturk 15 k into his 211 to even get to 68 mph,,heavy boat with a big hook in the hull..
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Old 08-19-2012, 02:43 PM
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Appreciate your honesty, but like I mentioned, this is the UK and powerboats are pretty rare. I am not too bothered about speed, I just need the prop well matched to the engine and drives ability.

Just as a matter of pure interest to you, this boat is worth approximately $24000 in the UK. So you can imagine what I am up against!! A new prop is definately the way to go!!!!!
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Old 08-19-2012, 05:08 PM
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I'm not sure what prop they sold you, but it's either a hell of a lot more than a 21" pitch or a few plug wires came off.

The first thing you want to know is that particular engine & drive combination is pretty marginal. Said another way, if you don't baby the hell out of it, the drive will grenade. That's why it was exactly a one year combination. So don't get too greedy with what you're looking for in speed. Also, avoid coming out of the hole too hard and never get that thing airborn.

Second, that motor is not meant to be screamed and 4600 - 4800 RPMs is about all you want to aim for. If you run more, you just run the risk of blowing the drive even sooner.

As far as another prop, if you want to gain RPMs, you want to decrease pitch. It's not surprising the a 21" pitch dropped your RPM's. It's more than a bit surprising that it dropped you so much.

Good luck mate!
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Old 08-20-2012, 01:02 AM
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Just a thought here.......would a LH prop cause this when a RH prop is needed????? If so can someone chime in and please explain how to tell the difference between the two? Thanks!
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Old 08-20-2012, 01:42 AM
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Originally Posted by mustangmark View Post
Just a thought here.......would a LH prop cause this when a RH prop is needed????? If so can someone chime in and please explain how to tell the difference between the two? Thanks!


It would go backwards surely?!
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Old 08-22-2012, 11:49 AM
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I had the opportunity to try a 15x17p prop today, and wow this thing flies now! I did not have the balls to run it past 5000rpm, but it was still climbing past 50mph at that.

Seems like such a small prop for such a large engine, but it must be better for the poor alpha drive as that is not under as much load anymore.
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Old 08-22-2012, 08:15 PM
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you left out a little information really needed to help the gear ratio of the drive. I had an 86 241 libby with same drive and motor with the 1.4x gear ratio, my current boat is an 87 454 with the bravo 1.5 drive I run a 21 pitch on it and get 4200-4300 my prop is mirage 3 blade but i get alot of slip only getting 43-44 mph but i know my boat is alot heavier than the 211 on my alpha drive i ran a solas 4 blade 19 pitch part number 1513-143-19 i ran 50 mph with that prop on my 241 might be a good choice to try i got mine from iboats.com for like 100 bucks. I think your speed your looking for is not out of reach on the lower end. the 60mph sounds high

but i would also agree your 454 wont live long if its all stock at 5000 rpm even though it says mag on the breather cover....that motor from the factory does not have the forged good stuff in and wont live at those rpms reall long.....i think 4800 is pushing it i like to keep mine in the 4500-4600 range.

but they also made a alpha drive that had 1.36 gears (this might be the wrong number but 1.36,1.32 somethinhg like that is the ratio number) this almost sounds like what your boat might have it would make a 21 pitch prop real hard to spin up and resond real well to the 17-19 pitch props. I think the large 15.3 dia might be a little much for that smaller of a boat. normaly heavy boats use the larger dia. i am not sure what your 211 trips the scale at. but your motor and drive is about 1200 pounds and i would think based on my 241 scaling 4000 without the power plant and 5200 with it....you should be about 4200 with drive

at least in the 241 they used the alpha drive 85-87 behind a 454 now despite what alot of ppl say these will live just fine in up to 400hp, it all depends on how you drive the boat like what others are saying....take it easy out of the hole, dont air the boat out. make sure you have a proper lifting prop and use your tabs to help the boat come on plane and let make the engine and drive to power through it.

keep us posted about what you figure out. what type of 17 pitch prop did you try

something that might be a good fit is tring a revolution 4 19 pitch its 14 5/8 dia 4 blade stainless but has great lifting properties with alot of rake alot of ppl with heavier sport boats have had good luck with it read on here a guy with 260 baja gained almost 10 mph with a labbed 21pitch rev 4 over his 21 pitch mirage. i am personal tring to find a 19 or 21 pitch one of these but the extra funds have not presented itself to me to get one. the do make this prop in 17 pitch too with the same dia. seeing its a 4 blade and assuming your 19 and this 17 are blades it should give better low rpm planing which would help the alpha, and being 4 blades will bring your rpms down a few hundred, but more than likely wont slow you down at all cause with the forth blade you should have less slip i plugged your numbers into the calculator http://www.go-fast.com/Prop_Slip_Calculator.htm at 5000 rpm using 1.36 ratio you have like 15% slip if you could get that down to 10 you would gain another 3-4 with the 17

i have read of several ppl getting +5mph with the rev 4 an like i mentioned personal talked with a guy that gain +10 with it and lab work

Last edited by bens87241; 08-22-2012 at 08:18 PM.
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Old 08-23-2012, 02:54 AM
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Thanks for the great response, lots to think about. The drive has 1.32 gears so the prop will spin really fast. The boats dry weight I believe is about 3200 lbs.
The engine is modified using forged rods, large oval heads, performer RPM intake and a 270XM cam. It gets up there really quick.
The prop I tried was a blackmax standard prop, sadly those things cost a forune in the UK.

I have concerns that a 4 blade prop might over torque the alpha drive, what do you think?
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Old 08-23-2012, 05:35 AM
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i would stay with a 3 blade with the alpha drive. you might wanna try a 1.5 drive and the 21p prop. try a smaller diameter.
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