prop pitch question

[plasmud]

I have a 1990 galaxy with merc 4.3L alpha one I/O
I get 4400 wot and my crappy fish-finder says i am hitting 32 mph

The boat currently has a prop that has printed on it 031025 14 X 19

I have a brand new prop the seller included with the boat that has A8 78118 A40 17P

my question is what will be the difference between the 17 and the 19 pitches. I looked around here for a bit with the search function and didnt find any thing quickly

 

[Bondo]

Re: prop pitch question

my question is what will be the difference between the 17 and the 19 pitches. I looked around here for a bit with the search function and didnt find any thing quickly

Ayuh,.... Because this question, 'n the answer will be found in the Prop Forum....

Btw,... The rpms should get up around 4800rpms with the swap...

 

[plasmud]

Re: prop pitch question

sorry, didnt even see the prop forum, I better keep my eyes open.
any thing else to worry about with putting on the 19?

 

[Bondo]

Re: prop pitch question

sorry, didnt even see the prop forum, I better keep my eyes open.
any thing else to worry about with putting on the 19?

Ayuh,... You said the 19" is on it Now...

 

[plasmud]

Re: prop pitch question

sorry, just mixed them up, I do want to know if putting the 17 P on will affect anything?
so it will run faster? but do i sacrifice anything like hole shot or planing? or load on the engine?

 

[Bifflefan]

Re: prop pitch question

OK, here goes.
19p at 4400 RPM runs 32 MPH. (I think thats what you said)
17p at 4800 RPM runs 32 MPH, or at 4400 RPM runs about 29 to 30 MPH.
You will gain a bit of hole shot with the 17p over the 19p, but lose speed at the same RPM.

 

[plasmud]

Re: prop pitch question

so what would be the reason to go with the 17 Pitch?

sounds like I lose top end? am I reading this right?

 

[Bifflefan]

Re: prop pitch question

so what would be the reason to go with the 17 Pitch?

sounds like I lose top end? am I reading this right?

read below

You will gain a bit of hole shot with the 17p.

 

[steelespike]

Re: prop pitch question

We need to know more about the boat size/model and dry weight if possable.
A speed by gps is much better.
If you read the stickies at the top of the page and the helps on the prop store page it will help you understand prop selection better.We'll be glad to help further.
Selecting a prop is like selecting a single gear in a car to do everything.
Some people focus on speed others water sports where hole shot is all
important,some just cruise etc.

 

[plasmud]

Re: prop pitch question

Thanks, well I am now reading all there is to read and i appreciate the help. the boat is a 21 foot Galaxy 228 walkaround I don't know the weight.
I don't need hole shot because it is a fishing boat and I wont be doing alot of speed , mostly just some cruising to spots and then trolling. My only two choices (without a new purchase) are the 19P which has a small nick on it and the brand new 17P i am thinking about putting on.

 

[steelespike]

Re: prop pitch question

A basic rule of thumb is a 1" change in pitch results in "ABOUT" 200 rpm change.
higher pitch lower rpm and so on.
So your 17" prop should increase rpm "ABOUT" 400 it will let your motor operate
closer to its max rating. This will improve hole shot make it easier for it to push a load of people and gear.Will likely stay on plane easier,less diddling with throttle.

 

[Howard Sterndrive]

Re: prop pitch question

verify your tachometer with a shop tach. Seems goofy to me.

I suspect you're not really turning 4400...

If you are turning 4400 and only moving 32mph with a 19P.... you have the wrong gears in your outdrive.

4.3;s have 1.84:1 gears...which at 4400 rpm and 19P, would have you at 40mph +/- a few

you could have 1.98 gears, or a faulty tach

or that 19P is really inefficient (i.e. beat up)

 

[plasmud]

Re: prop pitch question

A basic rule of thumb is a 1" change in pitch results in "ABOUT" 200 rpm change.
higher pitch lower rpm and so on.
So your 17" prop should increase rpm "ABOUT" 400 it will let your motor operate
closer to its max rating. This will improve hole shot make it easier for it to push a load of people and gear.Will likely stay on plane easier,less diddling with throttle.

Thanks for the explanation, I think i will try this prop this weekend.

 

[plasmud]

Re: prop pitch question

verify your tachometer with a shop tach. Seems goofy to me.

I suspect you're not really turning 4400...

If you are turning 4400 and only moving 32mph with a 19P.... you have the wrong gears in your outdrive.

4.3;s have 1.84:1 gears...which at 4400 rpm and 19P, would have you at 40mph +/- a few

you could have 1.98 gears, or a faulty tach

or that 19P is really inefficient (i.e. beat up)

I do know that it isnt the original outdrive. So you may be right. Plus the MPH gauge on the boat and the fish-finders match up and show me getting up to 30mph
tell ya what for simple striper fishing in the Hudson, i wouldn't want to go much faster that that anyway

how can i tell what gears i have in my outdrive?

 

[Howard Sterndrive]

Re: prop pitch question

how can i tell what gears i have in my outdrive?

100% accurate way is to remove top cap of upper and count teeth on the 2 gears (different drive pictured but same idea)

 

[plasmud]

Re: prop pitch question

what pitch prop would have come with the boat brand new, the 4.3L and the alpha one outdrive

 

[Robbabob]

Re: prop pitch question

Could be the ding in the 19" is more than just a ding. Causing loss of speed, but the rpm should have gone up with that.

Can we assume you are properly trimmed and not bogging down the boat?

Just a thought, or two....