prop question or advice

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I think I am all good now after this question is answered.


The prop on the boat my dad and I got a month and half ago was pretty beat up but still okay for use. My question is for a '16footer that is a inshore fiberglass center console which prop would be great for overall performance for the boat? The top speed is 30mph. Could be a little more if it had the right prop on it.

I read up last night that the 12x22 1.38 sticker on the lower unit itself is not the pitch and diameter but just the gear reduction info.


The info on the motor is that it's a 50 Mercury 5500max rpm and is a 2007 model. kw36.8

The prop number on what looks like the original BUT hopefully NOT the original prop IS --- 8167 2A40P12

so is the 12 the pitch?

And what size diameter is the prop?


Remember its a fishing\cruising boat for both of us and I was just wanting to know what I could change to get more performance OR just a better prop than what's on it deal.

Which brand too?

I see that in a West Marine catalog that Quicksilver props are the best for the boat as they are 150-200range.

But Blackdiamond and Turningpoint among others I found online are available.
If i get a whole host of mixed ideas on here I'll just call or talk to a local dealer to find out.

Just was getting advice on here that's all.
thanks
 
The correct prop is highly dependent on the specific hull shape and weight of the boat in a loaded configuraton, as well as the intended use.

There is no way you can expect to find the ideal prop by inquiring in a forum.

Having said the above, check with the manufacturer of your motor ans see what diameter and pitch ships standard with that motor. That will be a reasonably close compromise.

Alternately you can just test your configuration.
Load the boat as you intend to use it with gear, fuel, passenger(s). Remember to include things like coolers loaded with the weight you would run (food, becerages) and stowed in a safe running location (wide open throttle). Put passengers in their chairs, again the one they would use st full throttle cruise.

Insure you have an accurate tachometer installed on the motor.

Run at WOT for a few minutes, note if you like the attitude of he boat when fully trimmed, the speed/time out of the hole, and top speed (if accuracy is kmportant, use a portable GPS, not the speedo based on the pitiot tube in the boat or motor. If not, the relative speed is good enough. The "marine gauge" speedo will read high).

RPM should be at the specified Redline for the motor. If lower, you can decrease the pitch of the prop which will raise the operating RPM; conversely if higher then definitely increase the pitch.

Proper pitch delivers maximum power at maximum fuel economy at the highest speed.

With heavy loads you may want to increase the power at the expense of top speed and if the boat is light then uou can increase top speed but may find power to be inadequate.

Pitch is how big of a bite of water is taken with each revolution of the prop. You need to be careful thst there is enough power (like a higher numerically axle ratio) to safely climb waves in rough water. Best fuel economy is typically around 4000 RPM or so.

For a gearhead the following sometimes helps:
Compare 17 vs 21 pitch prop, and a 3:08 vs 4:11 rear axle ratio

A 3:08 ratio delivers less torque per revolution of the motor than a 4:11 ratio axle;
A 3:08 ratio delivers higher top speed than a 4:11 ratio at the same engine RPM

A 17 inch pitch prop delivers more torque to move the boat than a 21 inch prop
A 17 inch prop delivers lower top speed than a 21 inch prop at the same engine RPM

PRop diameter also plays a role here but you will find with a 50 HP outboard the diameter follows the pitch and doesnt change much. Racing Stuff is different, pitch and diameter will change in tandem to achieve specific goals.
 
Typically you get a prop with a pitch that allows you to run a WOT with one person aboard and 1/2 tank of gas.

If you remove the current prop it may be stamped somewhere on the hub.
 
Quote:
The prop on the boat my dad and I got a month and half ago was pretty beat up but still okay for use.


If it is pretty beat up then it is NOT okay for use!! You cannot judge performance with a less than perfect prop especially with only 50 HP. Not only does performance and fuel economy suffer but vibrations set up can ruin the seals in the lower unit.

There are several prop repair shops in Alabama:

http://www.southeasternprop.com/

Propeller Repair Services
11707 Memorial Pkwy SW # B Huntsville, AL 35803

Alabama Prop Repair
11014 Al Highway 21 N
Piedmont, AL 36272
256-447-8300

A dealer will sell you a new prop and send yours off to one of the prop repair shops to be refurbished and balanced. That's the one you keep in the boat for a spare.

A prop shop can identify your prop and make appropriate repairs. They can likely sell you a new one without the dealer markup too. It does not have to be a Merc prop. There are many brands that will perform as well or even better.

I sold boats in Bessemer, Jasper, Decatur, and Cullman some years back so I am somewhat familiar with the way things work with props.
 
By the way if the silver tag that identifies the engine serial number etc. says "Made in Japan" it is a Yamaha made for Merc.
The max RPM was usually given in a range such as 5500-6000 RPM. You can only guess at your current wide open throttle RPM 'cause the prop is buggered up.
 
Originally Posted By: RTexasF
Quote:
The prop on the boat my dad and I got a month and half ago was pretty beat up but still okay for use.


If it is pretty beat up then it is NOT okay for use!! You cannot judge performance with a less than perfect prop especially with only 50 HP. Not only does performance and fuel economy suffer but vibrations set up can ruin the seals in the lower unit.

There are several prop repair shops in Alabama:

http://www.southeasternprop.com/

Propeller Repair Services
11707 Memorial Pkwy SW # B Huntsville, AL 35803

Alabama Prop Repair
11014 Al Highway 21 N
Piedmont, AL 36272
256-447-8300

A dealer will sell you a new prop and send yours off to one of the prop repair shops to be refurbished and balanced. That's the one you keep in the boat for a spare.

A prop shop can identify your prop and make appropriate repairs. They can likely sell you a new one without the dealer markup too. It does not have to be a Merc prop. There are many brands that will perform as well or even better.

I sold boats in Bessemer, Jasper, Decatur, and Cullman some years back so I am somewhat familiar with the way things work with props.



I just knew it wasn't up to par. If I were to post a picture of it on here. Y'all would cringe.


I'll pull it off tomorrow and go to the mercury repair/boat shop and show them. If they can sell me a prop for less than $100 for now. I'll save my dad and I further [censored] from tearing up this engine.

Da&$.

Thanks

I bet as soon as I get a new prop the boat will scoot and get more hole shot and better cruising/plane.

I'm very glad I posted this. I've been out in the boat four times. My dad three times.
How can I post a pic on here to show you?

Add... The prop on it now is roughly 10.5" in diameter. I have about two inches clearance or 1" clearance for a slightly bigger prop.


When we got a newer 15hp evinrude on a 14' war eagle boat the boat could scoot. Since the first motor we put on it was a much older evinrude...and the pitch wasn't good for the boat. The '98 or '99 motor was and still a great motor for how our vee front welded/ back waters fishing johnboat.!


Tomorrow I will be going to get a new prop.

Weight of boat is 1150lbs, motor 209#, and 21gal tank. With weight limit I think it's 500lbs of gear and persons. Just an FYI.

I have done 3 different prop finders. Mercurymarine's , prop selector, and overton's...
But the options with pitch confuse me slightly though I do understand the pitch is how much the forward motion is... 13 pitch has a 13" forward in motion
 
Last edited:
FOUND it...
10.75X12


so with that I'm going to see about changing the pitch just a tad to make the rpms lower.

But the only catch is that I am not sure the tach on the boat is accurate which when I back off the throttle after WOT. It reads almost 6100 instead of what the motor's WOT is suppose to be of 5500rpms


thanks again
 
Any good repair shop should be able to cup the prop cheaply and easily when in for repairs.

Cupping really helps some setups to get a better bite of water especially when turning or starting out of the hole....
 
I'll see about that and keep this bent up prop for backup and store it in a compartment on the boat itself with a washer and nut and spacer.

ordered prop yesterday. It's a one piece mercury marine prop from west marine. It will arrive soon enough!!!

I did do a test run today just to see what the performance difference would be. At WOT and trimmed good I got 28.4mph gps as speedo doesn't work. I think all speedos on boats aren't accurate and get out of whack with the tubes and sender. Plus another boater today says his speedo doesn't kick on til he hits 35mph. So how simple of a fix is that? Do I need to mess with the gauge or blow out the air line going to the sender at the back of the boat.

So with that said the tach shows 6100rpms which I believe the tach is definitely off because the rpm range is 5500 for the motor. I got clarification yesterday that the motor DOES or should have a rev limiter on it. I think as I was trying WOT this afternoon that it did kick on as my rpm's suddenly dropped a 1,000rpms. SO it does work, but the gauge (tach) for it is off.

What does work is the fuel gauge and voltmeter like they are suppose to. The bad is the speedometer doesn't and the tach is iffy within itself. I might have to jerry rig that or get it fixed right OR find another tach for it and just replace it.

To make you laugh... I don't have to mess with all this on our trusty 15hp on our 14ft war eagle john boat... ha!
 
An accurate tachometer is a must when propping a boat. Replace it if you are unsure, it's not expensive. If the prop is chewed up then the engine will likely over rev. Run it with the new prop and check the RPM's. Are you 100% positive that only one RPM is listed for full throttle???? That just doesn't sound right unless it is a four stroke engine. Two strokes always have a specified range like 5500-6000.

You MUST have an accurate baseline with that new prop before you go fiddling with cupping or changing pitch.
 
After market props are much cheaper than factory props. Michigan Wheel is a prop manufacturer and sells quality products. I would not hesitate to buy their props and have many times over the years. Give them your prop numbers on your current prop, tell them what you want to achieve, and they will get you the correct prop if they make one for your application.
 
The type of prop you buy aluminum or stainless, should depend on the area you boat in. If your running in shallow water with lots of rocks or stumps. I would go with aluminum. you might damage the aluminum prop if you make contact, but might damage the lower unit if you have a stainless prop.The alum prop is cheaper to fix, so it's smart to carry a spare. Having a cupped prop will give a little more bite in the water. Getting the correct prop dialed in for your boat can be a trial and error event. Too much pitch and you loose rpms, too little and you'll over rev the motor.,,
 
Your tach might be accurate, a rev limited motor will rev higher than the operating range. The operating range (5500rpm) is what the motor is designed to run at continuously, the rev limiter is probably set around 6500rpm to keep the motor from damaging itself if the prop comes out of the water.
 
Just go to a good prop shop on the lake. The one I use in grove, he will put about 5 or 6 in special box, go out with you, change them on the water, and find the right one. For bass boats he can then fine tune the holes in the hub and the cup of the blade for your boat. All for about the same price as a prop mail ordered.

His prop got my old bass boat from 64 to 69 MPH. Better hole shot too.

Cost $200 and my old prop which I am sure he cleaned up and resold. He also made me a great deal on a rebuilt aluminum prop for $90 more in case I bent this one.

Rod

Rod
 
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