Please Enlighten Me!!!!

[Debbolas]

Ok, If you all get a moment I would LOVE to know how the whole Prop Pitch thing works...........
1) Boat size vs Prop Pitch?
2) How elevation affects prop performance?
Thanks!
Deb
:cool:

[riverbound]

You should probably call someone who specialises in props we used to use Hill propellors (before I had the jet) and they seemed to be very knowledgable and explained everything to us.

[gramps]

here is the beggining................
The pitch number is the amount of inches traveled forward for each revolution, ie; a 14 X 16 is 14 inches in diameter and will theoritically push your boat forward 16 inches for each revolution. Now the fun part. Every boat has a slip factor depending on its style, and no two boats will be the same. To find your slip factor, you must know the actual speed and rpm's, then mathmatically back into the slip factor. Prop science is the black hole of boating.

[RiverOtter]

It's real easy. You get your boat. All of a sudden your not happy with the way it's performing. So you listen to everybody and thier brother's opinioin. Go to a prop shop, give them a deposite on several props all with different pitches, cups, blade counts and spend the weekend at the lake trying to find the right friggin propeller. Simple :D
Really, you should talk to the people that built that awsome boat of yours they have probably tested every prop in the world to find the best fit.

[gnarley]

Originally posted by Debbolas
Ok, If you all get a moment I would LOVE to know how the whole Prop Pitch thing works...........
1) Boat size vs Prop Pitch?
2) How elevation affects prop performance?
Thanks!
Deb
:cool:
1) Boat size vs Prop Pitch? This can get very complicated! There is more to it than just size, and pitch and you must weigh in the other factors in determining which prop works best for your hull.
2) How elevation affects prop performance? When you change elevation you loose power, making it harder to turn the prop at maximum RPM since the blade may be too aggressive for the elevation. In order to counter act this you prop down to a smaller pitch to counter act the loss of engine power with a smaller prop the engine can turn.

[Debbolas]

Wow, so it is much more complicated than I thought.
With our old boat
(19ft Sea Ray-1step away from Bayliner.........LMAO, sorry I couldn't resist:D )
We had one prop for the river and one for Lake Powell because of the altitude.
RiverDave sold us an awesome prop that we have on our boat now....:D
I was just wondering...........;)
and we are super happy with our boat!

[Debbolas]

Originally posted by gnarley
1) Boat size vs Prop Pitch? This can get very complicated! There is more to it than just size, and pitch and you must weigh in the other factors in determining which prop works best for your hull.
2) How elevation affects prop performance? When you change elevation you loose power, making it harder to turn the prop at maximum RPM since the blade may be too aggressive for the elevation. In order to counter act this you prop down to a smaller pitch to counter act the loss of engine power with a smaller prop the engine can turn.
Thanks! I totally understand that. :D

[HavasuDreamin']

You want to prop your boat (family type boats) so that at full throttle, your motor is in its peak RPM band. In other words, if your motor makes peak power at 5,000 RPM, you should be able to spin your prop (at full throttle) 5,000 RPM. If you can't spin your prop to peak RPM, you need to move down in pitch (the second number on a prop). If you spin too much RPM, you need to move up in pitch.
At a higher altitude, there is less oxygen in the air. Motors work by mixing gas and oxygen and blowing it up. If there is less oxygen, you will make less horsepower. With less horsepower you will not be able to turn the same prop the same RPM (as you can at sea level). Thus, at altitude, to get back to the peak RPM band, you put a prop on with a lower pitch. The down side is you are now going slower.
Hope this helps.

[Kim Hanson]

Go for a good speed prop....30 -32 should work good..I run a 30 and will be moving up to bigger soon..........( . )( . ).....:cool:

[superdave013]

My props are all 16" pitch. WTF, am I building a slug or what?????? ;)

[Debbolas]

Originally posted by HavasuDreamin'
You want to prop your boat (family type boats) so that at full throttle, your motor is in its peak RPM band. In other words, if your motor makes peak power at 5,000 RPM, you should be able to spin your prop (at full throttle) 5,000 RPM. If you can't spin your prop to peak RPM, you need to move down in pitch (the second number on a prop). If you spin too much RPM, you need to move up in pitch.
At a higher altitude, there is less oxygen in the air. Motors work by mixing gas and oxygen and blowing it up. If there is less oxygen, you will make less horsepower. With less horsepower you will not be able to turn the same prop the same RPM (as you can at sea level). Thus, at altitude, to get back to the peak RPM band, you put a prop on with a lower pitch. The down side is you are now going slower.
Hope this helps.
Yes, thank you!
Ok, dumb question............how do you know if your prop is spinning at 5,000rpm? (or your motors peak power) I mean you can't count the revolutions.................

[superdave013]

Originally posted by Debbolas
Yes, thank you!
Ok, dumb question............how do you know if your prop is spinning at 5,000rpm? (or your motors peak power) I mean you can't count the revolutions.................
It's on one of those round things on the dash. Kinda like the red and green lights. There for a reason. :cool:

[sigepmock]

Posted a similar question in Out Drive Tech....but what are the benefits/downsides to 3, 4, or 5 bladed props?
My new boat came with a 5 bladed 21P, any benefits to getting a 4 or 3 blade?
Chris

[Dr. Eagle]

Here Deb.........
Propeller Calculator (http://www.go-fast.com/Prop_Slip_Calculator.htm)
Altitude robs horse power from your boat. since you don't have a transmission with multiple gears like you do in a car... the HP loss is very noticable.
You generally lose about 3% of engine HP per 1000 ft of elevation if I remember my de-ration tables from our engine generator sets.
This loss is very noticable... for instance Tahoe is at 6,200 ft. You lose almost 20% of engine output due to the thinner air. For this kind of loss you have to pitch the propeller about 4 inches less than at sea level. For my boat I'd have to go from a 21 pitch to a 17 pitch to keep acceleration the same and the top speed will be in the neighborhood of 15mph less.

[Debbolas]

I do remember our old boat, if we didn't change the prop, we had like NO horsepower......

[mirvin]

Originally posted by superdave013
It's on one of those round things on the dash. Kinda like the red and green lights. There for a reason. :cool:
He's talking about the "Tachometer". It's usually next to the "speedometer". IT tells you what RPM your motor is turning.
mirvin
Hey Sigepemock, I think the differences you'll see in the 3,4, or 5 blade props will be in things like: acceleration, bow lift, prop slip, etc. You should find someone with a similar set up (hull, power, drive) as you and see if they can give you any pointers as per thier experience.
mirvin

[Debbolas]

Originally posted by mirvin
He's talking about the "Tachometer". It's usually next to the "speedometer". IT tells you what RPM your motor is turning.
mirvin
Thanks!
I had NO IDEA what he was talking about, so you just look at your Tachometer to see if your prop is working........Got it!!

[superdave013]

Deb, sorry to be the smart ass.
The tach only tells you how fast the engine is turning.
From that you can tell if your prop is in the ball park. Also it tells you if something changed. Less RPM could mean you are down on power. Maybe due to a higher elevation of lake or maybe an engine tune up problem.
The tach is an important gauge.

[mirvin]

Originally posted by Debbolas
Thanks!
I had NO IDEA what he was talking about, so you just look at your Tachometer to see if your prop is working........Got it!!
Basicly yes. It's like this. THink of your prop as your "wheels":
Lets say your car has 15" wheels and at 50mph your tach says 2500 rpm, ok?
If you put smaller wheels on the car, it will change the other numbers. Because you have to spin a smaller wheel faster to acheive 50 mph you'll end up with a higher rpm.
So if you change the prop it will effect the other numbers as well.
You just need to understand that Prop pitch, speed, and rpm all work together. Depending on what you want out of your boat you'll find the right combination of pitch, rpm and speed.
mirvin- trying to confuse you more!!

[Debbolas]

Originally posted by mirvin
Basicly yes. It's like this. THink of your prop as your "wheels":
Lets say your car has 15" wheels and at 50mph your tach says 2500 rpm, ok?
If you put smaller wheels on the car, it will change the other numbers. Because you have to spin a smaller wheel faster to acheive 50 mph you'll end up with a higher rpm.
So if you change the prop it will effect the other numbers as well.
You just need to understand that Prop pitch, speed, and rpm all work together. Depending on what you want out of your boat you'll find the right combination of pitch, rpm and speed.
mirvin- trying to confuse you more!!
NO!
I totally understand that!!!
Thanks!:D
Debbolas<---------"the prop is the wheels";)

[RiverDave]

Debbolas, I wouldn't said like the "wheels" more like the gears in a transmission.. Lower pitch prop = lower gear.
Elevation doesn't really have any affect on a prop's performance, it has affect on the motors performance. Higher the elevation the "thinner" the air, the less HP the motor makes, the less RPM you'll get, the slower the prop will spin and the slower the boat will go.. kapeesh? ;)
I was hoping Scream would get a chance to do some comparison data between that prop and your old one, but after talking to him I guess he never got a chance too, and this new one already got a little dinged up from some gravel and a POS launch ramp. :(
From what he said though he was cruising at 50mph fully loaded with fuel and 7 people or something?
Either way I was going to send him another PM. .
RD

[mirvin]

Originally posted by Debbolas
NO!
I totally understand that!!!
Thanks!:D
Debbolas<---------"the prop is the wheels";)
Do you guys ski or wake board or anything? If so, you may want to keep a second prop that gives you more power out of the whole, which would in turn lower you top speed performance. At the same time if you want to go as fast as you possibly can, the prop for that might make your boat seem sluggish out of the hole but you'll be rewarded by a higher top speed.
It's a delicate balance becuase weight inside the boat effects performance. If you get the prop set to where you get max top speed with just two people in the boat, and then put 8 people in with two coolers and everthing else, yopur performance will change.
The main goal is to make sure you don't have excessively high rpm at top speed.
mirvin

[gramps]

Hey Deb..............maybe you need to change the skull on the side of the boat to a dinged prop with smoke rising from it.
In your extra time you might want to look at this site http://www.props.net/ look at the right side of the page.

[Debbolas]

We were cruising with 13 people on board at 50!!!:D
on the way to pizza at the POS Wawheap Ramp. ( I guess they are dumping gravel off the end each day to try to extend the ramp):(
Scream is the driver, so he knows about the performance, I just pass out drinks and put sunscreen on the driver:D as needed;)
Ok, if the thin air effects engine performance..............why did our old Sea Ray's horsepower improve when we went to a smaller prop?
Debbolas<----------REALLY going to clean the boat now
:D
How are you set up for Jerky Dave? Do you need anymore yet? I wouldn't want to get kicked off the RRL board for lack of Turkey Jerky :D
(jk);)

[mirvin]

Originally posted by Debbolas
Ok, if the thin air effects engine performance..............why did our old Sea Ray's horsepower improve when we went to a smaller prop?
(jk);)
Probly because the smaller prop allowed the motor to run at higher rpm's counteracting the thinner air/feul ratio.... If you take your boat to a higher elevation the thin air will effect the performance of the engine........changing the prop will counter act this effect.....to some extent.
mirvin

[Scream]

Do you guys realize that at some point tonight she's gonna try and explain all this to me and believe in her heart that she makes sense???
:rolleyes: :rolleyes:
I'm gonna have to start drinking early.
Scream <--- thinking about what goes good with Vodka, Rum, and Scotch (mixed).

[mirvin]

I would love to hear that conversation!!!
mirvin:D

[gramps]

hey Scream, I know where there is a Mexican resturant not too far from where you "work".............Margartias by the pitcher!!!!!

[Scream]

Originally posted by gramps
hey Scream, I know where there is a Mexican resturant not too far from where you "work".............Margartias by the pitcher!!!!!
Meetchya there in an hour or so...

[Dave C]

LMAO
Originally posted by Scream
Do you guys realize that at some point tonight she's gonna try and explain all this to me and believe in her heart that she makes sense???
:rolleyes: :rolleyes:
I'm gonna have to start drinking early.
Scream <--- thinking about what goes good with Vodka, Rum, and Scotch (mixed).

[Dr. Eagle]

Originally posted by Debbolas
Ok, if the thin air effects engine performance..............why did our old Sea Ray's horsepower improve when we went to a smaller prop?(jk);)
Deb <------------------------------Defying the laws of physics..........:D

[ROZ]

Originally posted by Debbolas
Ok, If you all get a moment I would LOVE to know how the whole Prop Pitch thing works...........
1) Boat size vs Prop Pitch?
2) How elevation affects prop performance?
Thanks!
Deb
:cool:
Why don't you take God's advice :D

[RiverDave]

Originally posted by Debbolas
Ok, if the thin air effects engine performance..............why did our old Sea Ray's horsepower improve when we went to a smaller prop?
It didn't improve "horsepower" The HP isn't affected by what pitch prop is on the boat. It probably pulled out of the hole a little better and then the RPM's went higher at top end. This is the same as if you were driving up the street in third gear and then (sticking a smaller prop on the boat) putting it into 2nd gear. HP didn't change but acceleration is better, and top end is slower MPH with higher RPM's.
How are you set up for Jerky Dave? Do you need anymore yet? I wouldn't want to get kicked off the RRL board for lack of Turkey Jerky :D
(jk);)
I'm ok for right now, but I'll be hitting ya up soon. ;)
RD

[Debbolas]

So, I go out to clean my boat (Mr. Clean Magic Eraser is the bomb)
and you all are just sitting here discusing my ignorance of prop mechanics..........................LOL:D
Gotta go vacumn the boat now...........
Debbolas<------------------understands....the prop is the gear that makes the boat go. The law of physics is suspended around Lake Powell because of the Anasazi, so your smaller prop will make your boat go faster....The Tachometer is a very important gauge. God wants me to visit a website. All is well:D

[Havaparty]

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