Question...but please don't switch this to Props

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thunderroad

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because there is never anyone there. I need to figure out exactly which prop I need to get for my 69 Mercruiser 160 sn 2497444. None of the charts I've found go back this far. I want a 21 pitch, aluminum, but want to be sure and get the correct one. I've come across a lot of contradicting info in my search.

thanks
 
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Dhadley

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Re: Question...but please don't switch this to Props

What diameter prop are you running now?
 
T

thunderroad

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Re: Question...but please don't switch this to Props

14.25....I had a 21 which worked perfectly but it got destroyed. I can't make out the numbers on it. My spare is a 19 which is great for the hole shot but gets the WOT up to near 5000, the last 4-500 of which have no effect on MPH. The 21 would get the MPH up near 40 with WOT of 4000 or so. I could plane out and cruise around 3400 or so and seem to save a lot of fuel....not to mention wear on my nearly 40 year old engine.

thanks


usually someone chimes in and says they're moving a thread when it happens.
 
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Dhadley

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Re: Question...but please don't switch this to Props

Just look for a 14 1/4 x 21. We'll assume that since it's aluminum it's a 3 blade. That's a pretty common size. Personally, I'd go with stainless but that's entirely up to you.
 
T

thunderroad

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Re: Question...but please don't switch this to Props

Are the splines the same? I see props listed on ebay saying things such as "for alpha 1" "for Mercruiser 1A" "fits V6 Mercruiser" and things like that. One in particular was same as new but in the picture, the blades looked different than the blades on mine. Mine have a lot more metal on them. What does this mean?
I'm certainly not locked in to buying used from ebay. It's just that the lists I see to order new ones don't actually show my drive.
The prop shop said they wouldn't trust fixing mine. One blade was bent at almost a 90 degree angle halfway up. They seemed to think it would probably break it they tried to work it back into shape. Plus, he said it looked like the rubber in the hub was beginning to crack. He suggested I just get a new (different) one. He doesn't sell them, just repairs.
 
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Dhadley

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Re: Question...but please don't switch this to Props

Not all 21's are created equal. There's blade area, rake angle, trailing edge cup, leading edge cup, progressive pitch and on & on. So yes, some 21's will look different.

If the prop has a Merc hub, is 15 spline and not for a Merc "fat shaft" it will fit on your drive. Whether it works properly or not may be another question.
 
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thunderroad

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Re: Question...but please don't switch this to Props

"Whether it works properly or not may be another question". This is precisely my question.

Thanks for the help, dhadley. It is appreciated. I guess I'll just keep digging. Where can I learn more about props? It's like they're some mystical, magical item that everyone is afraid to discuss.
Maybe whichever moderator it was that switched this from engines (where there are always a few dozen people participating at any given time) will chime in and explain to me which prop I should use. I would think the emphasis would be more on sharing knowledge and trading discussion than making sure a question is stuck neatly in it's predetermined slot.
(insert rolling eyes icon here, please)
 
jimmbo

jimmbo

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Re: Question...but please don't switch this to Props

Any idea how old your old prop is? I ask because if your prop is pre 80s it might not be cupped. That would make a difference how how a new 21 performs.


quote "It's like they're some mystical, magical item that everyone is afraid to discuss."

No they are not Magical, Mystical and part VooDoo, yes.
It is however, very difficult to give an answer that can be cast in stone regarding props. Dhadley said it well
 
Tail_Gunner

Tail_Gunner

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Re: Question...but please don't switch this to Props

May i ask what type of boat you have???
Is it a open bow, tri-hull, cuddy do you know the length or maybe the weight......what motor is in the boat a 4cl 6cl or 8. Do you know what type of performance you are looking for that is Top Speed, Cruising, or Water Sport's

Give these guy's that type of info and you will get some good answer's..
 
T

thunderroad

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Re: Question...but please don't switch this to Props

My boat is a 19'6" Formula F-190. Not open bow. In my first post I mentioned it was a 69 Mercruiser 160 sn 2497444 which means it's an inline 6. In my second post I mentioned what I was looking for in performance and compared the 21 I'm wanting to replace with the 19 that I have for a spare.

"I had a 21 which worked perfectly but it got destroyed. I can't make out the numbers on it. My spare is a 19 which is great for the hole shot but gets the WOT up to near 5000, the last 4-500 of which have no effect on MPH. The 21 would get the MPH up near 40 with WOT of 4000 or so. I could plane out and cruise around 3400 or so and seem to save a lot of fuel....not to mention wear on my nearly 40 year old engine."

I'm not sure what the boat weighs, although it doesn't feel all that heavy and the interior is fairly sparse. Fuel tank (17 gal) is in the bow. My question is...since I can't positively identify, by number, the 21 that was destroyed, what do I need to know about blade size and such to make sure I'm getting a prop that will perform like I want?

thanks
 
Tail_Gunner

Tail_Gunner

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Re: Question...but please don't switch this to Props

Somebody here has to know the drive type .......how's about a liitle chirp...;)
 
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Dhadley

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Re: Question...but please don't switch this to Props

The Alpha is the older Mercruiser drive that they used for years. Very standard shape & function for the time. Typically we don't see the need for a high rake or hi-tech prop on a sterndrive unless it's a performance drive. We'll assume the Alpha is rather low so the hi-tech props won't yield the performance you're looking for or paying for.

I'd look at the standard aluminum props from Mercruiser. Those tend to be expensive even for aluminum. If it were mine I'd look at the Stiletto line here at iboats. The simple 14 1/4 x 21 should be fine. It's really hard to compare props when we don't know what brand or style you're running now. All we have to go by is that you say you'd like to by a 21.
 
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thunderroad

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Re: Question...but please don't switch this to Props

Ok...after a bunch of cleaning and magnifying, the numbers on the prop that I liked are 48 79576A-4 21P. I Googled the number and got a few conflicting things. One called it a 15 1/4, one a 14 1/4. One even said it was cupped and would compare to a standard 23 pitch prop. There is a small area near where the blades meet the hub that has a little cup to it, but I can't say as I see such a thing on the rest of the blade.
So I guesss this is the one I need to find, or one that would be a comparable replacement. I'll check into this Stiletto you mention.

thanks
 
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stevens

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Re: Question...but please don't switch this to Props

Sounds like you'd be more than happy with a 21P Black Max, which is a very decent and versatile aluminum prop that can be picked up for a very reasonable price.
 
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thunderroad

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Re: Question...but please don't switch this to Props

Yeah....just checked them out. That just might be the answer. Thanks...
 
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Crownie2

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Re: Question...but please don't switch this to Props

You can but a brand new one for about $100.
 
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thunderroad

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Messages
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Re: Question...but please don't switch this to Props

That one looks pretty nice, but is almost too purty for running in the Missouri River.
When you say "slip", do you mean physically slipping in the hub or is that a term for just not pushing water past a certain point? The reason I ask is that when I was running about 4600 rpm with the 19 and realized I had throttle left and opened it on up, the rpm went to 5000 and the boat didn't seem to pick up any speed at all. I quickly backed it back down to 4000 or so and went about my business but wondered if there was a problem with the prop.
As is obvious, I know very little about the workings of or physics behind props.
thanks for all the help
 
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