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21..20.. 23.. 22?.. pitch it to me!!

212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
I started out (purchased boat) with a wounded 21p 14.25" 3 blade.. eh.. it was wounded, so its hard to say much, but the boat seemed to struggle..

I dropped to a 14" 20p 4 blade (alum).. it hit the rev limiter, but I really liked it jumping on plane and holding plane @ 16~17mph, but over 3400rpm..

I jacked that prop up, guys, and I've no clue what I hit.. something hard, but zero damage to the skag, and I didn't fell anything at all.. didn't even notice it until it was out of the water, which tells me it happened at the ramp... And, I was sober as a cat (as always while playing capt).. I MUST have hit something dang hard as it was coming up the trailer.. anyway..

I just slapped on a 14" 23p 4 blade.. it was cheap for a new prop, alum, and brand new.. hey, I'm still experimenting, anyway... Guess what? I like it a lot!!! I can come out of the shot at around 7~8 seconds or so, hit 45mph with a four people and loaded down nowhere near rated wot (i hit 4kish rpm, limit window is 4400-4800).. I held nice plane, trimmed right, with spray right under the helm, and 25mphish, 3200rpm.. I really dig that.. what I don't dig is idle speed maneuvering, where it moves quite a bit quicker than the 20p.. I reckon I could get used to that, though.. one strange thing this four blade does, the other didn't: the stern really pushes higher, and changes the boats attitude in the water below plane speeds.. almost like the nose dives..

I have a three blade stainless 22p 14.5" sitting on my workbench.. I've been staring at it... You fellers with experience on such matters: would you rec a stainless THAT much more than aluminum?? The only reason I'm not bolting it on right now is because I'm really surprised the 23p wasn't too much, and more so because I don't wanna beat it on whatever it was that took out the 20p before I figure out what that was....

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    bat32bat32 Member Posts: 161 ✭✭✭
    To start off I am far from a pitch expert.  The only thing I can add though is if you put the stainless prop on and strike the hard you will damage more than the prop.  The inner workings of the lower unit wil fail before the prop.  Just something to put in your back pocket.

     

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    mvnmvn Member, Moderator Posts: 744 mod

    Am I reading your comments right?  4,000 RPM WOT with the 23"?  If so, the engine is lugging WAY too much.  Have you had a look at the pitch calculator I posted recently?  Now that you have real world data, you can fine tune my spreadsheet so that it can reasonably predict your theoretical performance numbers for your rig.

    Mark

    Good,  fast,  cheap.... pick two. 
    2019 MTX20 Extreme

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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    I was shy of wot @ 4k... I had some throttle left, and could have hit 4400 no doubt about it.. maybe 4500... I had a five month old and three adults in the loaded boat, and traffic off the channel was crazy.. when I near unpredictable weekend warriors, I back off and go into a reactive posture... Hopefully this week, if not today, I'll get a good wot run with just me and a tank of fuel.. I'm all but positive I'll be between 4400 and 4800..

    I found what I hit this morning.. it was at the ramp.. some **** tossed a street sign in the drink at the base of the ramp, with the metal pole laying at roughly 45* angle and pressed against the sea wall... Another boater was mad as all get out wrestling with it.. he hit it with his outboard, while loading up.. what makes people do things like that I'll never understand, but it has teenager prank written all over it.... I winder how many other people fouled props before this was discovered?

    Mark, I did use your calculator from the other thread.. and I appreciate it greatly.. I was right on the line, mathematically, of having too steep a prop.. but it seems to like it... I can still plop on the 22p ss prop just to see... It's almost perfect because it not only drops a pitch, but it picks up diameter- it should almost be a 'push' so far as the engine is concerned.. except, I don't know how much difference the ss will make over the aluminum as far as flex and weight (which is what I assume affects the rpms, right?)..
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    mvnmvn Member, Moderator Posts: 744 mod

    Oh, ok Drew.  I agree that the 22" will probably be bang on.  Flex, or lack thereof, of the ss prop will have a greater effect than rotational mass.  Cupping will also make a big difference.

    BTW, what drive package are we talking about here?

    Mark

    Good,  fast,  cheap.... pick two. 
    2019 MTX20 Extreme

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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    Alpha 1.8:1, 4.3l.. 212 liberty edition... Which, I'm thinking is the perfect coastal family bow cruiser.
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    mvnmvn Member, Moderator Posts: 744 mod

    OK then.  Gut instinct tells me the ss 22" will be perfect and most efficient for cruising.  It will be interesting to see your WOT data with it.

    Mark

    Good,  fast,  cheap.... pick two. 
    2019 MTX20 Extreme

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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    DA - A 23" pitch three blade will usually be too "tall" for a 4.3 with an alpha 1.8:1 unless you have the 4.3LX which might handle it. Usually the 4.3LX with your profile boat likes a 21"pitch 3 blade, but depending on your hull specifics a 22" might be bang on. I love stainless props as they usually have cupping that performs better across the rpm band. Their best feature is that they do not deform/deflect at higher rpms causing rpm shifts. As mentioned already you could misalign your prop shaft if you really whack the ss prop. I have dinged ss props before and not hurt my drive units but you will hurt your wallet if you ding your ss prop as they are far harder (read more expensive) to repair. Good Luck MT
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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    The submerged enemy here isn't submarines or rocks, its sand.. aluminum props last maybe a season, I'm told.. everyone gets into the sand at times, its inevitable.. its why everyone uses ss props, if for that simple reason..

    I feel a lot better about what happened to the 20p prop, even though I'm still tweaked about it.. I reckon I can consider myself lucky there was not an expensive ss on there during that encounter.. at the least I'd be fixing that prop.. it could be I'd be buying a new one and a new lower unit, too.. who would do that and why is beyond me.. it was just plain mean..
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    Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    edited July 2013
    Mean it was. You have to give an ss prop a pretty decent whack on a hard item to bend the shaft, from my experience, as for sand - that will just clean an ss prop! Just keep the sand out of your cooling system. A guy once brought a Baja with twin supercharged 502s into my friends marina. It was seriously overheating. He called me to come over for a look. The hoses, channels, everything was full of sand. This guy had been moored on a sand bar and revving it for the beach bunnies. That was expensive. New impellers, a complete cleaning of filters, gaskets and two blocks cleaned. I'm sure he put one of my friend's kids through college by the time it was over! MT
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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    had a full boat yesterday with four adults, two kids, one infant, and a bunch of gear.... wot was 4k rpm... the 22p three blade will be better. 
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    hunterdalehunterdale Member Posts: 19 ✭✭
    Due to the difference in the flex of props between aluminum and stainless you should drop at least 2" in pitch when going from aluminum to stainless.  The 23" alum was still overpropped and I think the 22" ss will be as well.  A 21" ss will act close to the same as a 23" alum.  I'd go to a 19" or 20" ss.  Most ss props have a little more rake in them and this is why I think less pitch will give you better overall performance.   
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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    you're likely right, but I already own the ss 22p three blade... I'm hoping it is what I'm looking for..
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