Prop question
 

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.

fixx
 

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..

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!!!!!

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!

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?!

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.

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

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?

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.

with a 1.5 gear ratio for the prop to spin once my motor( and i should be more specfic here and say the crankshaft ) turns 1.5 time( which if looking at the dist rotor would be 3/4 of 1 turn) so your set up when the prop goes around once the crankshaft will go 1.32 so what it means is your prop is actualy spinning closer to engine rpm than a 1.5 ratio so yes your prop will spin more times at 1000 rpm that a 1.5 ratio at the same rpm which is why you had trouble with 21 pitch prop the extra pitch without the extra ratio was just oo much for the motor to handle......with the lower number gear ratio it puts more load on the motor. If you use the prop slip calculator plug in your drive and pitch you had at 4400 you would have a theoretical speed of 60mph with 0 slip if you want to compair apple to apple and say you do put a 1.5 drive in a 21.5 pitch would get you the same theoretical speed. now seeing how expensive stuff seems overthere i bet a outdrive is even more crazy. and alot of work really not needed cause you really wont gain anything. i think the gears ratio is right for that lighter boat, with the 17 pitch you gained cause again it was not overloading the motor .

The forged rods will allow you to turn a few more rpms safely but if the pistons are still cast i would still limit the rpms. If it was a car it would one thing you go there and then slow down on a boat we run those rpms ofr a longer time. and i really dont think the 4 blade prop will put more load on the drive than a 3 blade your boat weighs in the same no matter if there is a 3 or 4 blad prop on the shaft.....so the output shaft and gears are seeing the same weight and force load to move the boat the same speed. now the faster you go the more load there will be on the shafts and gears. i also repluged your info with the 19 pitch into the calculator and came up with almost 20% slip a little high.....now a 4 blad will help with this think of as that ever force load you boat is putting into the water to go 50mph all that force is now going through 3 blades. with a 4 blade the same amount of force will be spread among another blade lowering the force pounds each blade will have to carry. this is why slip goes down with a 4 or 5 blade prop. I have never heard of someone saying the blew a drive cause they put a 4 blade prop on. something to keep in mind that boat will be out of the water quite a bit at those speeds so a good driver shower to help keep the alpha cooler while going the higher speeds might be a good investment to help the drive live.

i still feel a rev 4 in 17 pitch would probable be the ticket.......if in the search bar on this site if you type liberator.....you should be able to scan down and find a thread from dtile he had the baja 260 that with a rev4 gained 10 mph and gained rpm over his mirage now he had 21 and used a 21 rev 4 he gives a good compair to speed and rpms on his boat. now each boat is differant but its food for thought. if i recal even with a no worked over rev4 he still gained 5 mph over the mirage at the same rpm

I will definately look out for a rev4, sounds like the way to go. Don't worry about the drive shower, I fitted those before this boat ever hit the water!! Thanks for taking the time to help, it is greatly appreciated.

Sometimes your advice is really useful, this in not one of those times.

My 211 never had a hook in the hull, straight as an arrow with a yard stick.

I had an 87' 211 until a few years ago, I had the 350/260 combo and the best prop on it was 21" Ballistic @52.xxmph, the 454's were 3-5 mph faster, so 55-57 should be doable no problem. I believe they all came with a 1.5 ratio drive, but that doesn't mean somebody hasn't changed yours. A 21p prop should work well in the diameter you tried, but it obviously couldn't get on plane and that is why your speed was so slow. I would try another 21" prop and if that is to high for rpm, I would try a 19" 3-Blade 14-14.5 inches which will be easy on the alpha drive, but that should be to low a pitch for that combination.

I also agree with everyone, keep that thing under 4800rpm, 4600 is about perfect for that motor.

I ran the serial of the drive and it is definately a 1.32. It was specifically made for the 454 alpha set up I believe.
Top end speed is not that important, I just want to get the best out of the engine and drive. That 15x17p is a lot of fun though!!

Ok there you go, use this: http://www.rbbi.com/folders/prop/propcalc.htm

For that hull I always saw between 11-12% slip for the prop on my 87' 211 that puts you dead on almost for a 19" prop @ 55mph @4600rpm. Depending on the prop you may see a little higher, or lower slip. Good luck!!!

if you are happy with your 17 prop now and it fits all your needs stay with it.....

so what did you do or figure out for your prop?