Mercruiser Propeller

[ahunter40631]

Well......

Just got off the water to discover the propeller was bent...(it’s a stainless propeller with a 20 pitch).
Looking to buy a new propeller(prob just an aluminum prop cause the stainless ones are EXPENSIVE to say the least. Couldn’t find a 20 pitch in the aluminum... how much does the pitch matter? The motor is a 1990 4.3L mercruiser and the drive is an Alpha One.. any advise appreciated...

 

[jimmbo]

As the Title says "Read this First"

https://forums.iboats.com/forum/gen...p-questions-and-topics/295058-read-this-first



"how much does the pitch matter?" A lot!!!. It is what will determine what load the engine is under. Too much Pitch and engine is overloaded and can be damaged. Too little Pitch and the engine over revs and that too can damage the engine.

What RPM was the engine attaining at WOT with your current Prop. You engine likely has a WOT range of 4400 - 4800 rpm.
Any clue as to what Prop it was, regarding Make and Model?

Going from the SS to an Aluminium will affect things, some of which are, but not limited to are:
Top Speed
Grip on water
Overall boat handling, and how the boat rides on the water

I would also check the Propshaft for Run Out, as Shafts have to known to bend on Impacts when Stainless Props are in use.

 

[porscheguy]

Were you happy with your stainless prop? Props whether aluminum or stainless can be repaired to brand new condition. It’s not really cost effective to repair aluminum, but a stainless stainless prop can usually be repaired to like new condition for a fraction of the price of new.

 

[ahunter40631]

I have a pic of some numbers that are on the prop and it is stamped (Turbo) also, other than that I have no idea which brand it is...I’ll try to attach that picture. The boat had this prop on it 10 yrs ago when I bought the boat... my wife won’t let me spend $500 or $600 on a new stainless prop so my plans are to have this one “fixed/repaired” if possible.
in the meantime if I could buy an aluminum prop which is much more affordable it will let me get the boat back on the water fast... I haven’t been able to find a 3 blade 20 pitch aluminum prop in my google attempts.. I did see a 4 blade 20 pitch aluminum prop... That is why I was asking about the pitch and the difference it makes... if I could figure out which aluminum prop to buy it would give me a spare prop after I get my stainless prop fixed. We like to just go to the lake, ride around and pull the kid around on the tube. I’ll dig thru my pics in a bit and try to post boat motor and drive model numbers shortly as well.
I can’t figure out how to post the pic so the numbers stamped on inside of prop are: M141 14X20
stamped on the other side is TURBO there is also a small engraving that says “M20”

 

[Chris51280]

I have the same year and engine you got. I run a 4 blade 14x19 aluminum and get to 4500rpm at 40mph. I like it. I have also a 3 blade ss 23p prop that came with the boat which I still have to test. It is a little dinged up but I heard it is not uncommon for the 4.3 to run with a 3 blade 23p prop. get almost 50mph out of it. so I heard.

 

[jimmbo]

What RPM were you getting at WOT with this 14" X 20" prop? If you don't know, any recommendation is going to be a Guess at best, even if we have information such as Gear Ratio, WOT rpm range, what boat is it on.

 

[jimmbo]

I have the same year and engine you got. I run a 4 blade 14x19 aluminum and get to 4500rpm at 40mph. I like it. I have also a 3 blade ss 23p prop that came with the boat which I still have to test. It is a little dinged up but I heard it is not uncommon for the 4.3 to run with a 3 blade 23p prop. get almost 50mph out of it. so I heard.

I would bet, that you will go slower with the 23 than you go with the 19. It will take forever to get on plane, if you even get on plane

 

[Chris51280]

Maybe. Like I said, it came with the boat and looking around here on iboats, I'm not alone there with the 23p.

 

[QBhoy]

I have the same year and engine you got. I run a 4 blade 14x19 aluminum and get to 4500rpm at 40mph. I like it. I have also a 3 blade ss 23p prop that came with the boat which I still have to test. It is a little dinged up but I heard it is not uncommon for the 4.3 to run with a 3 blade 23p prop. get almost 50mph out of it. so I heard.

If your numbers with the 19” (even being a 4 blade) are correct....you are going to be disappointed to the moon and back if you try that 23”...I wouldn’t even bother trying it.

Some 4.3’s will turn a 23”....but that entirely depends on what boat it’s in and what gearing....most will not.

 

[Chris51280]

my outdrive has a 1.98 ratio vs the standard 1.81. Not sure why though. came like this

 

[ahunter40631]

I purchased an Aluminum 3 blade Rubix 3 propeller made by Solas.... it is a 21 pitch. I had to special order the hub kit for it to fit my boat since they did not carry it in stock. I have found a place in Georgia that will rebuild my 20 pitch stainless steel prop for $250. The aluminum prop will just be a back up until I can get stainless prop repaired. I typically only run around 4000 rpm max, it may run slightly faster than that WOT...

Dows anyone see any concearns with using the aluminum 21 pitch prop versus a 20 pitch stainless still prop? The guy at the store said the only difference I would see is a 100-200 rpm change because of going up 1 degree in pitch..

 

[Chris51280]

I dont think you will see much change since the aluminum ones tend to deform more vs the ss. They say to switch from ss to al to go up 1 pitch.

 

[QBhoy]

99% of props for this boat will be an odd number pitch. Only a few props come in even or 1” increments for these drives. Or someone has made or fashioned an outboard prop to fit. If the latter is true, you might not have a good base numbers data to find a normal prop for it. If not and your 20” was fine and in the range...a 21” ally will be just fine...especially if you aren’t that fussed about such things. As long as you are in the rpm range you’re good. Anything higher or lower and you’re on a fast track to a new engine !