Propeller Selection

LivinnSadley · **Joined:** Tue May 29, 2012 12:47 pm **Posts:** 38

Hello All,

I know this topic may have been beaten to the ground already but it is hard to use the search tool to find pertinent information.

I currently own a '93 Sundowner 215 (5.0 EFI OMC, Cobra drive) and have an aluminum 15x17 prop.

- What is the best prop for hole shot for my specific boat?

- What is the best prop for the most efficient mileage for cruising?

- Locally there is a 14.5x17 Stainless Steel prop for sale for $100 and I'd be interested if it can work

- How do I find out the gear ratio of my boat? While doing some research I am trying to learn about prop slip and gas efficiency...

Thank you in advance,

Corey

deafwish · **Posted:** Fri Apr 24, 2015 6:43 pm

Credit to iBoats:

http://www.iboats.com/basics/choose_right_prop.html

ESSENTIAL DATA REQUIRED
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

LivinnSadley · **Joined:** Tue May 29, 2012 12:47 pm **Posts:** 38

Hmm, from memory. I'll have to check out the exact numbers once I can get the boat out this spring.

1) Looking for better hole shot and gas mileage (not sure both are possible with the same prop)
2) Not sure of prop manufacturer (at work, shhh) but I know it is a 3-blade aluminum prop
3) 15"x17p
4) est. 44-46mph @ <5k rpm with 50% tank gas (~25gal) and 2 people. I'm not worried about top speed.
5) OMC 5.0 EFI Cobra, 200 propshaft HP
6) Four Winns Sundowner 215, 1993, 21.5'l x 7'9"w 3,450lbs dry weight

I'm mostly trying to see if my boat is running efficiently. I'd like better mpg mostly.

Who can help me?

Jdpber · **Posted:** Mon Apr 27, 2015 12:30 pm

i started a prop thread a while back that members posted their prop, boat, specs. take a look and you may find some helpful info their..

BUT to start you need to base line and take down some data on your current setup to best address the issues. as some boats run better than others and people that more shit around than others.. these little variables make a big difference. Hell even a broken keg can effect a few mph. to generalize A vs B is next to impossible without the hard baseline data to use in recommending a prop..
you can post your current information here and add to the database
http://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=13646

Jdpber · **Posted:** Mon Apr 27, 2015 12:47 pm

If i was you i would go to a 4 bade< i did this and it is more torque with a little less top speed. but maintains a better 30s cruise and holds plane better.

LivinnSadley · **Joined:** Tue May 29, 2012 12:47 pm **Posts:** 38

The problem is the water I ride will not be navigable for at least a month so getting this data will take time.

Maybe I can narrow my question for now...

I currently have an aluminum 15x17 3-blade prop.

I am currently looking at a Michigan Stainless Steel 3-blade 14.5x17

How may this SS prop differ for me in performance being 1/2" smaller in diameter but Stainless compared to aluminum.?

There is one for sale locally for $100 and may disappear quick.

deafwish · **Posted:** Mon Apr 27, 2015 4:16 pm

Although it's cheap, it's not going to give you your desired end result.
Invest in a SS 4 blade prop of the same pitch and same/ smaller diameter.
5000RPM sounds a couple of hundred RPM higher than it should be turning, so the 4 blade will knock off approx 200RPM.
I bought a Solas HR Titan 4 and it totally transformed my boat.
Look at the Amita 4, for a more cost effective solution.

278TheNiseeII · **Posted:** Mon Apr 27, 2015 5:09 pm

Aluminum props flex under load and after a few years your 17 pitch is bent to a less pitch. That may be why your rims are high.
You definetly need a ss prop. Size may be a challenge but the $100 one would not be a bad place to start as a baseline. You could always sell on ebay later.
4 blade is great for hole shot but will hurt you on top end compared to a similar design ss 3 blade. And a good 4 blade is not cheap.

Good luck.

deafwish · **Posted:** Mon Apr 27, 2015 5:54 pm

278TheNiseeII wrote:

Aluminum props flex under load and after a few years your 17 pitch is bent to a less pitch.

While an AL prop will flex slightly under load, it certainly will not reduce it's designated pitch over time!
SS prop's can be manufactured with more cupping and rake, which also increase their performance over AL.

Jdpber · **Posted:** Tue Apr 28, 2015 9:14 am

Another thing to take into account is that a SS prop when grounded or contacts a solid object has NO give where an Aluminum has give. So take into account if your waters have stumps or floating logs that an aluminum will be safter for your lower unit and less likely to cause shaft or gear damage with impact. Where as a SS prop with no give can damage the shaft and lower gears if impacted abruptly with an object.

SS is heavier rotational mass so the same exact spec alum vs SS will turn different rpm as the alum spins freer than the ss. This also has to be taken into account.

ALum is more cost effective and can yield the same results as a SS if properly sized to the application.

I have a SOlas 4 blade Amita and have been very happy with he hundred dollar prop. I also can buy 2-3 different sizes for different desired performance results for the same money as a SS so this is more beneficial to em to have a cruising prop. a tow prop. a speed prop all for the same money.

WITHOUT BASELINE TRUE NUMBERS AND SPEEDS we cannot accurately recumbend a prop... ALSO remember that not every prop is splined the same so you need a prop splined to your specific out drive shaft..

john55c · **Posted:** Tue Apr 28, 2015 8:51 pm

I bought an OEM stainless prop on eBay and it increased hole shot, top speed, and fuel economy. 3 blade prop. One of the better purchases I have made for the boat....FWIW.

www.iFourWinns.com

Propeller Selection

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