switching to stainless steel prop - told to lower pitch?

rbhawes

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Joined
Jul 17, 2017
Messages
13
so for starters, i'm operationg a 2012 Glastron GT205, 4.3 motor. My original aluminum prop is a 14 1/2 Diameter, 19 Pitch.

I was chatting with propmd.com and was recommended the SS propeller, that is a 14 1/4 X 17. Does this sound accurate to lower the diamer and pitch when switching to SS? I was always told that you don't want to change diameter and pitch.

if it helps, the prop I'm looking at is http://www.propmd.com/michigan-whee...43-14-1-4-x-17-with-hub-kit.html?options=cart
 

rbhawes

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Joined
Jul 17, 2017
Messages
13
I was also recommended, if I decided to go to a 4 blade to get the Michigan Wheel Apollo 4 Blade, part # 993204 which is a 14 3/8 X18. I understand a 4 blade will get me better hole shot, and stay on plane longer.

typically in my boat, we're just cruising - going to restaurants or hitting a local beach. rarely do we go to tubing, in fact I bought a tube last year, and never once used it. Maybe eventually we'll go tubing once in a while - but hard to say.

what is everyone's thoughts?
 

porscheguy

Chief Petty Officer
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Jan 17, 2013
Messages
441
A few pieces of pertinent info are required.

Which 4.3 do you have? MPI? Carb? What’s the HP?

What’s your outdrive gear ratio? Mercruiser tends to sell the 4.3 with either a 1.81 or a 1.62.

Finally we need to know your performance data. Top speed measured with gps is best, and RPM at top speed.


Now fortunately, a quick google search on your boat produced a test of a 2012 gt205 w/4.3 MPI, and 1.62 ratio. They show it running 49mph at 4800 rpm with the same prop you’ve got. I don’t know if the magazine stops at 4800rpm because that’s the redline, or if 4800 is all it has in it. Either way, I’m impressed that the boat is pulling those speeds which indicates 8% which is quite good for an aluminum prop. But as a rule, prop slip decreases as prop rpm increases. So the performance is within reason.

If you went from a 19 to a 17, even if you reduced your slip from 8% down to 5%, you’d still wind up losing 4-5mph top end, which sort of negates the purpose of a SS prop.

If your boat performs and is equipped like the boat in the test i read, stick to a 19” pitch.
 

porscheguy

Chief Petty Officer
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Jan 17, 2013
Messages
441
I’m not sure why they’d recommend a 17P on a 3 blade and 18P on a 4.

For general cruising purposes stick to the 3 blade. Unless you’re actually dissatisfied with its current hole shot, the 4 blade probably won’t give much benefit.

Where are you located?
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Stick to a 3 blade 19”
also, the prop you mention is a waste of time. Get a laser 2, tempest, Enertia or similar.
If she sees anything like 4800 rpm currently, no need to drop 2” pitch.
Only exception would be if for some mad reason you put a big rev 4 on it. But that would also be silly.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
When I switched from AL to SS on my 5.7 VP SX, I had the 21 AL VP prop. I had a 20 in RAKER from my OMC outboard, so I figured I'd give it a try after rehubbing it. In this case the drop of 1 in. in pitch resulted in the same RPM as before, but the top speed went up a couple of MPH, and the boat handled and rode substantially different(better). When placed side by side there were major differences in the blade design and blade shape between the two props.
As I, and other have mentioned in the past, comparing different lines/models/brands/material is an Apples to Oranges comparisons, and what works for my boat/engine/setup/usage, may or may not work as well for you. Sometimes you just have to bite the bullet and buy a prop(with exchange privileges), if beg/steal/borrow hasn't yielded results.
 

rbhawes

Cadet
Joined
Jul 17, 2017
Messages
13
A few pieces of pertinent info are required.

Which 4.3 do you have? MPI? Carb? What’s the HP?

What’s your outdrive gear ratio? Mercruiser tends to sell the 4.3 with either a 1.81 or a 1.62.

Finally we need to know your performance data. Top speed measured with gps is best, and RPM at top speed.


Now fortunately, a quick google search on your boat produced a test of a 2012 gt205 w/4.3 MPI, and 1.62 ratio. They show it running 49mph at 4800 rpm with the same prop you’ve got. I don’t know if the magazine stops at 4800rpm because that’s the redline, or if 4800 is all it has in it. Either way, I’m impressed that the boat is pulling those speeds which indicates 8% which is quite good for an aluminum prop. But as a rule, prop slip decreases as prop rpm increases. So the performance is within reason.

If you went from a 19 to a 17, even if you reduced your slip from 8% down to 5%, you’d still wind up losing 4-5mph top end, which sort of negates the purpose of a SS prop.

If your boat performs and is equipped like the boat in the test i read, stick to a 19” pitch.


Thanks. So i'm actually running the CARB motor, Unfortunately I don't know the motor specs, as I received no paperwork when I purchased the boat, but I do know it's the 4.3 TKS motor w/ the alpha one out drive. I believe it's the 190 HP.

I haven't ran with a GPS, but typically at top speed i'm cruising about 45 MPH at about 4500-4800 RPM.

I'm definitely satisfied all in all with my boats hole shot, I get on plane fairly easily, and for what i'm doing - the boat operates fine. Keeping the same MPH with lower RPM of course would be ideal.

The other prop i'm looking at is a Turning Point Mach 3 Express, part number 31501922.

http://shop.paxtonco.com/storefrontCommerce/itemDetail.do?item-id=27126&item-number=31501922

which tells me its a 14.25 X 19.

I'm located in Pax River, MD, typically i'm cruising in the Patuxent River, usually don't touch the Chesapeake, but maybe the mouth of the Chesapeake when i'm going to a few restaurants.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Again I’d advise sticking to a good stainless prop. Otherwise it’s just for show really.
If there is no problems with hole shot, you 100% don’t need to drop in pitch. With a good stainless you will see more grip on the water, less flex and keeping shape and intended pitch when underway. Might drop your revs a little, but if you get a good prop it a win win situation.
Try and stay away from the cheaper stainless props. It’s often been the case in testing that the standard ally black max prop out performs them...so there is a real risk you may lose performance.
 

dingbat

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Joined
Nov 20, 2001
Messages
15,413
I'm located in Pax River, MD, typically i'm cruising in the Patuxent River, usually don't touch the Chesapeake, but maybe the mouth of the Chesapeake when i'm going to a few restaurants.
My favorite restaurant in town is the Tiki Bar.....lol
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
15,413
Are you local to Pax as well?

last I saw, unfortunately last I heard they're not opening the Tiki Bar this year.

Live in Western Howard County (for now) but have fished out of Chesapeake Beach and Solomon's longer than I care to admit.

From what I can remember, lots of fond memories at the Tiki Bar....lol
 

porscheguy

Chief Petty Officer
Joined
Jan 17, 2013
Messages
441
I’m in western Anne arumdel county about 15 minutes from Annapolis. I grew up in st Mary’s county. I just read about the Tiki Bar. The deceased owners widow better get off her butt and run the place, or find people to run it. That’s a viable business. The opening of the place in the spring is a big event. The problem is that if the place sits vacant, people go elsewhere. The value of the place has more to do with its revenue rather than the facility itself or even the location.

i haven’t gone boating around there in 20+ years, but I think it’s on my list this year.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
so for starters, i'm operationg a 2012 Glastron GT205, 4.3 motor. My original aluminum prop is a 14 1/2 Diameter, 19 Pitch.

I was chatting with propmd.com and was recommended the SS propeller, that is a 14 1/4 X 17. Does this sound accurate to lower the diamer and pitch when switching to SS? I was always told that you don't want to change diameter and pitch.

if it helps, the prop I'm looking at is http://www.propmd.com/michigan-whee...43-14-1-4-x-17-with-hub-kit.html?options=cart

Usually a SS prop is a high performance screw. That means that for a given dia and pitch it will bite more water or bite what water is uses harder which places additional load on the engine and drops rpms.

However, what is usually not taken into consideration is that a cupped, high rake, thin bladed prop with the trim set to optimum can and will bring the hull out of the water, like the bow lift feature that high rake produces, and by getting the hull out of the water the drag is reduced which unloads the engine and allows it to come on up in rpms and the result is actually higher speed with a prop of the same pitch.

Minor diameter changes in the pitch ranges of a given series of props is part of the prop design and is of little importance.
 
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