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-   -   Prop selection issues HELP PLEASE (https://www.offshoreonly.com/forums/general-boating-discussion/279413-prop-selection-issues-help-please.html)

akaboatman 07-11-2012 09:59 AM

You leave the boat in the water ? Pull it out an clean the bottom.

BBCLiberator 07-11-2012 10:44 AM


Originally Posted by onesickpantera (Post 3727676)
Since that boat came with a OMC it probably came with a Raker prop. I have some friends with early 90s 221 Libs and they came with 20" Rakers. One has a stock 454/330hp and runs low/mid 50s with a 20 Raker. I think his drive is a 1.43 so that puts him at about 10 slip.

The could see high slip numbers on the standard Mirage 21 but the high slip numbers on the Mirage+ 23 are baffling.

The boat this thread is about has a Bravo on it, but you are correct, mine cam with a 14.5x20 Raker on the OMC. Viper props were the other big stock OMC prop.

That's where I am at with the slip, something isn't adding up, we'll know more once he verifies exactly what he has.

onesickpantera 07-11-2012 12:21 PM


Originally Posted by BBCLiberator (Post 3727739)
The boat this thread is about has a Bravo on it, but you are correct, mine cam with a 14.5x20 Raker on the OMC. Viper props were the other big stock OMC prop.

That's where I am at with the slip, something isn't adding up, we'll know more once he verifies exactly what he has.

I saw it had a Bravo. I was just stating what they came with since it was asked.

Either he is trimming up much higher than he thinks or the engine and drive were raised when they swapped to a Bravo. The X dimension on Libs are VERY deep and there is no way he should be blowing out props with little trim.

I would verify the X and trim angle.

BBCLiberator 07-11-2012 01:44 PM


Originally Posted by onesickpantera (Post 3727807)
I saw it had a Bravo. I was just stating what they came with since it was asked.

Either he is trimming up much higher than he thinks or the engine and drive were raised when they swapped to a Bravo. The X dimension on Libs are VERY deep and there is no way he should be blowing out props with little trim.

I would verify the X and trim angle.


This one started life with an alpha. But I get your point.

And I totally agree with that, that's what has me confused too, blowout shouldn't be an issue for sure.

onesickpantera 07-11-2012 01:59 PM


Originally Posted by BBCLiberator (Post 3727857)
This one started life with an alpha. But I get your point.

And I totally agree with that, that's what has me confused too, blowout shouldn't be an issue for sure.

Ahhh I didn't catch the Alpha part.

I agree you should be able to trim a Lib to the moon before it blows out. On my buddies Libs I'd guess the propshaft is 7-8" below the boat.

BBCLiberator 07-11-2012 02:30 PM


Originally Posted by onesickpantera (Post 3727868)
Ahhh I didn't catch the Alpha part.

I agree you should be able to trim a Lib to the moon before it blows out. On my buddies Libs I'd guess the propshaft is 7-8" below the boat.

I actually asked him if he for some reason has a shorty lower on it, but I don't know or have the dimensions to look for.

Yeah on both my libs you could trim them forever before they would blow out.

It's always fun to try to unravel a mess from the past when you have no history....

bens87241 07-11-2012 07:08 PM

Yes this boat did come with the alpha drive and mow has the bravo. I dont think they raise or motor. my prop shaft is at least 8 inches below the boat........i will try to take a measurement

yes the boat sits in the water......no its not all covered in stuff. I have the bottom painted with seahawk paint and bioside.......after 6 months last year sitting in the water there was very little build up just a thin slim coating that you could use you hand to rub it off. I recoated this year with the same stuff i keep the bottom wiped with a rag every week at the beacj and the side above the paint scrubbed with a brush to keep it from building up. no there is not a build up or marine growth....i hate to leave it sit but bottom paint does a good job......i cant drive a truck up to lake erie every weekend....and the dock only cost me 300 a year cheaper than driving the truck every weekend.

With the trim gauge not working the only thing i can think to do is measure from the water to the prop shaft........trim it till it looses grip shut it down and measure again to see how much........but its truely not even halfway to the limit switch.....the limit switch stops it about 1/3 of the through the travel and trailer button gets the rest of it. And just before someone asked no i do not have the buttons mixed up.

If someone know the length of a bravo 1 reg drive compaired to shorty i will measure to find out. What i do know is at my dock the water depth by my gauge is 3.5 feet below the bottom of the boat.......it has a shoot through the hull transducer. i am 6'4" and the 3.5 feet of read is is actualy about halfway up my chest i would say about 4 feet deep in honesty cause the soft mud bottom i sink in about 6 inches or so into the soft mud. at this 3.5 to 4 feet of water if my drive is all the way down there is 8 inches so before before the lowest part of the skeg not sure if that helps.......but to me that does not seem like the drive has been raised too much

IF someone has a 241 liberator on a trailer that has a bravo drive if they could measure from the prop shaft to something referance point on the boat.....the drain plug , top of the back of the boat...... remember my boat is in the water.....so points below water will be hard to hold against and measure......

And i dont think comment on the engine rpm ratio is right.. there is 2 crank turns to 1 cam so the piston in each cylinder goes up and down twice to make 1 revolution. Rpms on a tach are a measure of cam shaft rpm. but i know the crank drives the coupler and input shaft.....and its direct to the crank......so maybe i am thinking of it wrong.... so maybe the prop would turn faster now MR Maine has my brain turning....lol ok thinking out loud hear. the crank drive the input shaft the ratio is for the input to output......1.5 input to 1 output input is equal to crank revs not cam revs... 1 crank equals half cam. so yeah Mr Maine is right .75 dist rotor to 1 prop its been a long week already my brain is toasted....i RETRACT WHAT I SAID Mr Maine is right.... anything more 3/4 dist rotor would be a higher number ratio 1.65 anything less would be a lower number ratio 1.3x



thanks again to all who are coming up with ideas to help. i would rather cross the t's and dot the i's than spend money wastefuly

onesickpantera 07-11-2012 07:26 PM


Originally Posted by bens87241 (Post 3728036)
With the trim gauge not working the only thing i can think to do is measure from the water to the prop shaft........trim it till it looses grip shut it down and measure again to see how much.

That is a good idea just so you know.

The Mirage + 23 didn't have open vent plugs did it?

bens87241 07-11-2012 09:18 PM

no it does not even have the spots for the vent plugs part number 48-13704 23p should not matter either way....boat has rear exit through no exhaust goes through the outdrive and prop the mirage 21 does not have them either did any or the pirage or plus have them???

onesickpantera 07-11-2012 09:45 PM


Originally Posted by bens87241 (Post 3728160)
no it does not even have the spots for the vent plugs part number 48-13704 23p should not matter either way....boat has rear exit through no exhaust goes through the outdrive and prop the mirage 21 does not have them either did any or the pirage or plus have them???

Got ya. Even if you have thru-hull exhaust it can give you some serious ventilation and even blow out.


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