Alpha prop replacement... size questions?

Dante04SRT

Dante04SRT

Petty Officer 1st Class
Joined
Jun 30, 2007
Messages
311
I am looking to get a little more "out of the hole" performance out of my 3.0 Merc. My current prop is a 19 pitch, unsure of size; probably a 14.5?

My question is this, what size prop would be ideal for my boat? Its a 16.2" Deep V Hull style boat with a 3.0 Merc. Should I go down to like a 17 pitch? Also, am I required to stick with a 14.5" style or is there something else that will work with my Alpha One?
 
wire2

wire2

Lieutenant Commander
Joined
Jun 25, 2007
Messages
1,584
Re: Alpha prop replacement... size questions?

Prop diameter is not that critical, there's little discernable difference between a 13.75, 14, or 14.25.

There will be a noticeable boost in hole shot from 19 to 17 but your wot rpm will jump by 350-500 rpm.
If you're in the proper range now keep an eye on the tach.

Your top speed will be proportionately decreased, as will fuel economy.

It's like driving a manual transmission car, shifting from 5th to 4th and leaving it there.
 
tommays

tommays

Admiral
Joined
Jul 4, 2004
Messages
6,768
Re: Alpha prop replacement... size questions?

Your in the ballpark right now

What is your real speed and WOT RPM


If you drop down to a 17" prop it will get on plane really quick BUT with the 2:1 reduction in the 3.0 outdrive it will really limit the top speed ;) to about 32 MPH :confused:


I have a 17" 3 blade 19" 3 blade and a 20" 4 blade To use with different boat loads on my 3.0




Tommays
 
mkast

mkast

Lieutenant Commander
Joined
Nov 6, 2002
Messages
1,934
Re: Alpha prop replacement... size questions?

The prop is the limiting factor of engine RPM.
If your boat engine is running in the manufacturers' recommended wide open throttle RPM, changing the prop will only hurt engine performance.
Prop the boat for a good hole shot, the engine RPM will be above the recommended range.
I'd look at losing some weight on the stuff you're carrying in the boat.
 
H

Hashi

Chief Petty Officer
Joined
Sep 19, 2007
Messages
502
Re: Alpha prop replacement... size questions?

tommays said:
Your in the ballpark right now

What is your real speed and WOT RPM


If you drop down to a 17" prop it will get on plane really quick BUT with the 2:1 reduction in the 3.0 outdrive it will really limit the top speed ;) to about 32 MPH :confused:


I have a 17" 3 blade 19" 3 blade and a 20" 4 blade To use with different boat loads on my 3.0




Tommays
Click to expand...

Hi Tommays,
I'm thinking of getting different size props for different loads, as well. I just got the boat about two months ago and find at loads of four people or more I don't get up on plane as fast and go about 45 mph at 4500 rpm WOT. But, if its just me and the wife, it gets up plane immediately and does 55 mph at 5200 rpm at WOT. I have a 260 hp Mercruisers Alpha One I/O and my question to you is...Is it hard to change the props on these motors? I've read on other threads that prop changes has be done by a mechanic because they're so complexed and require the right tool.

Rich
 
J

Jerico

Petty Officer 1st Class
Joined
Sep 22, 2006
Messages
254
Re: Alpha prop replacement... size questions?

I have a 17.6 open bow with the 3.0 & Alpha 1. The 17 pitch that was on it when I bought it made it run up to around 5500 rpm at WOT at 32-35 mph. I switched to a 19 pitch. Dropped the rpm's down to 4600 and brought the speed up to about 45. It takes a sec to get on plane, but not excessively slow. We mostly cruise or tube so it doesn't matter to me. It pulls a tube fine. It will pull a strong skier up, but drags a bit. If I was pulling a skier more I would probably switch to the 17 when pulling, then switch back to the 19 for cruising. All it takes is the right size wrench.
 
nlain

nlain

Commander
Joined
Nov 17, 2005
Messages
2,445
Re: Alpha prop replacement... size questions?

Tail_Gunner has the answer. Smart Tabs will do wonders for your boat.
 
S

stevens

Senior Chief Petty Officer
Joined
May 4, 2005
Messages
799
Re: Alpha prop replacement... size questions?

... just to elaborate on these last comments; the Smart Tabs will help you get on plane much easier and at lower speeds, even with your current prop. That way, you don't have to sacrifice top-end speed either by going to a too-low pitch prop, nor will you have to fiddle around with changing props back and forth (which is very easy, by the way, at least when the boat is on land).
 
C

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Alpha prop replacement... size questions?

Another option no one has mentioned yet, replace your current prop with a stainless, same pitch etc, only PORTED.

The porting allows a measured exhaust leak to cavitate the prop enablilng the engine to jump rpm to the upper limits, the boat literally climbs up out of the water and as the nose falls over it feels as tho it 'shifts' in second gear, the water flow as the boat gains speed seals the ports, the prop bites into the water, engine rpm drops and you're off!Engine rpm climbs as the boat accelerates.

Merc makes these in most all sizes and for all gearcases.

I just bought another factory merc prop and discovered it is WRONG for my o/b gearcase.

This should be at my door any day now and I'll be looking for someone that needs a factory merc V6 o/b or alpha or bravo 1 in 14 X 23 ported SS 3 blade
 
C

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Alpha prop replacement... size questions?

That could work and it's a very good price.
 
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