Changing prop diameter

[tiqueman]

I did some quick searching and havent found anything. Just curious, if you have for instance an X447 and cut it down to 45, is it now the same as an X445 or has the pitch or anything slightly changed?

I know there are x445 available so why would you cut a 447 down, but an (R) is not. I cut down both a L and R 447 last night to 45 for a twin I have. And like I said, just curious if anything other than diameter changes.

[siberianhusky]

It still has the pitch of the 47 mm which is 65.8 so it becomes a 1.46222 x 45.

[Boaterguy]

it would change other factors, like siberian husky stated, but a 2mm change (1mm off each blade) would not be so much to affect your setup in any noticeable way. of course do not match an X445 with a cut down 447, but if you cut both, I don't see a problem.

[tiqueman]

So comparitively speaking, it has more pitch than a stock 45? I guess thats what I was getting at. I know that since I didnt physically bend or tweak anything, I didnt change pitch, but a cut down 45 is not the same pitch as a stock 45. Correct?

[Boaterguy]

yes, that is correct.

[siberianhusky]

Lift seems to stay about the same as the larger diameter, at least on the small mono's I've done this on. Boaterguy must have been into the crack again! there is a huge difference in performance! The difference in load is amazing! There is a difference between a 38 and a 40mm prop store bought prop why on earth would you think 2mm wouldn't make a difference if you do it yourself?

[tiqueman]

2mm certainly makes a difference. I got some gps runs earlier today. I'm going to throw some stock 447s on it later in the week for comparison of both speed and temps.

[Rich]

So comparitively speaking, it has more pitch than a stock 45? I guess thats what I was getting at. I know that since I didnt physically bend or tweak anything, I didnt change pitch, but a cut down 45 is not the same pitch as a stock 45. Correct?
The pitch of both props is the same, so is the total pitch after you cut it down, all you have done is made it into an x445. The first "4" in x447 and in x445 denotes the 1.4 pitch of the blade. The 47 and 45 denotes the diameter. The math works out the same. 2mm is a big change in performance especially at the RPMS we run at.

[Boaterguy]

I meant that the pitch that changes with a 2mm diameter larger prop cut down will not have alot of affect, I agree that 2mm is a large change, but a cut down 447 vs a 445 is not much different.

[tiqueman]

Putty shows something is different. If you take a 445 and a 447 cut down to a 445 the blades do not lay the same. My findings cause me to disagree. A 445 and a cut down to 445 is not the same

[Rich]

Putty shows something is different. If you take a 445 and a 447 cut down to a 445 the blades do not lay the same. My findings cause me to disagree. A 445 and a cut down to 445 is not the same

Hmm thats interesting...can you compare a 447 cut down to 445 and a stock 445 with some data? I am curious as to see what happens, since I have an x447 to modify.

[Rich]

I meant that the pitch that changes with a 2mm diameter larger prop cut down will not have alot of affect, I agree that 2mm is a large change, but a cut down 447 vs a 445 is not much different.

Ok I get what you were trying to say now :laugh:

[Boaterguy]

haha good because I don't even understand what I said.

[siberianhusky]

x445 has 63mm pitch, an x47 has 65.8 divide by 45 and you get 1.462 pitch ratio.
You still have 65.8mm of pitch just in a 45mm prop instead of 63mm of pitch, this is a major difference at these sizes and rpm. Boaterguy at least get a running boat before offering opinions on something you have no experience with.

[Boaterguy]

yeah, whatever you say.

[Rich]

x445 has 63mm pitch, an x47 has 65.8 divide by 45 and you get 1.462 pitch ratio.
You still have 65.8mm of pitch just in a 45mm prop instead of 63mm of pitch, this is a major difference at these sizes and rpm. Boaterguy at least get a running boat before offering opinions on something you have no experience with.
Can you explain the reason for your math?

[LarrysDrifter]

Pitch stays the same as the prop came from the factory if all one does is reduce the diameter. Scott has a 45mm diameter prop with the pitch of an X447. Simple as that. He did not tweak the blades, so pitch is still stock. Same thing Husky was saying.

[tiqueman]

That's how I got confused about all this. 45x1.4 and 47x1.4 and I was imagining it as siberian said. Even though its cut down, its still the 65.8.

I can and will test the differences using an eagletree and a gps. Now my gears are turnin???

[Rich]

Pitch stays the same as the prop came from the factory if all one does is reduce the diameter. Scott has a 45mm diameter prop with the pitch of an X447. Simple as that. He did not tweak the blades, so pitch is still stock. Same thing Husky was saying.
Which pitch are you talking about, they both have the same 1.4 pitch (the distance it would travel with one revolution in a soft medium), the total pitch is different since each has a different diameter. This is where I get confused. :confused2:

[tiqueman]

But I think.. and I could be wrong, but its manufacuted relative to proportion? I dunno, its just the way I imagined it which is how all this started. And even though all 4 series props are 1.4, their pitch numbers are all different which I understand how and why but that's what got me to thinking as siberian and larry, its still the 47s pitch.

[Rich]

But I think.. and I could be wrong, but its manufacuted relative to proportion? I dunno, its just the way I imagined it which is how all this started. And even though all 4 series props are 1.4, their pitch numbers are all different which I understand how and why but that's what got me to thinking as siberian and larry, its still the 47s pitch.
I think its because the 447 is longer from the drive dog side to the prop nut side, if you were to cut the whole blade down by 1mm per side it would be a stock 445 hmmm maybe thats the missing link..?

[siberianhusky]

The PITCH RATIO is 1.4 multiply that by the diameter of the prop and you have the pitch. Simple as that, always been that way. If you reduce a larger diameter prop you don't lose the pitch unless you bend the blades.
Argue as much as you want put a 0-1" dial indicator on your prop 60-70% out from the hub and measure the pitch, cut off a few mm and remeasure the pitch it stays the same. And yes pitch is measured about 60-70% from the hub, don't ask me why I don't know, just been told that and it works.
A x447 cut down to 45mm is not the same as an x447, it's closer to an x547 but with different some characteristics.
1.4 x 47 = 65.8 mm pitch for a stock x447
1.4 x 45 = 63.0 pitch for stock x445
65.8 / 45 = 1.4622.
The 47mm prop has 65.8 mm pitch, you cut 1mm of the tip end of each blade so now it's 45mm, you haven't changed the pitch of the original 47mm prop as it's cast in at the factory.
So take your pitch of 65.8 and divide by the diameter to get the pitch ratio.
Pitch is measured 60-70% of the distance from the prop hub.
You are only changing one number in the equation the diameter unless you physically bend the prop you are not changing the pitch, unless you remove a ton trailing edge, but these are different mods.

[Rich]

The PITCH RATIO is 1.4 multiply that by the diameter of the prop and you have the pitch. Simple as that, always been that way. If you reduce a larger diameter prop you don't lose the pitch unless you bend the blades.
Argue as much as you want put a 0-1" dial indicator on your prop 60-70% out from the hub and measure the pitch, cut off a few mm and remeasure the pitch it stays the same. And yes pitch is measured about 60-70% from the hub, don't ask me why I don't know, just been told that and it works.
A x447 cut down to 45mm is not the same as an x447, it's closer to an x547 but with different some characteristics.
1.4 x 47 = 65.8 mm pitch for a stock x447
1.4 x 45 = 63.0 pitch for stock x445
65.8 / 45 = 1.4622.
The 47mm prop has 65.8 mm pitch, you cut 1mm of the tip end of each blade so now it's 45mm, you haven't changed the pitch of the original 47mm prop as it's cast in at the factory.
So take your pitch of 65.8 and divide by the diameter to get the pitch ratio.
Pitch is measured 60-70% of the distance from the prop hub.
You are only changing one number in the equation the diameter unless you physically bend the prop you are not changing the pitch, unless you remove a ton trailing edge, but these are different mods.
I wasn't arguing, just wanted a clear explanation, this explanation is what I was looking for! Thanks!

[martin]

What you also have to take into account is if you have a given diam that your measuring at 70% from the hub is if you cut the diam down you have to recalculate 70% of the smaller diam & not measure at the same point as 70% of the bigger diam prop. Martin.

[tiqueman]

Like siberian has said now several times, they are different. That's all I wanted to confirm. A cut down prop to a 45mm is NOT the same as a prop that comes as a 45mm. Thanks

[siberianhusky]

Who on earth wouldn't use common sense and measure at the same place?:doh: How can you calculate anything if you don't measure from the same point each time you make a change? I'd hate to buy one of your boats if you just pick random spots to measure from when installing hardware!

[785boats]

Another thing to consider is that the cut down 47mm prop will still have a slightly wider blade from the leading edge to the trailing edge than the stock 45mm prop. This will be grabbing slightly more water than the stock 45mm blades & therefore loading up the motor a bit more but hopefully delivering more speed if the motor maintains the same revs as the original 45mm prop allowed it to run.
Just a thought.
Paul.

[FloatDaBoat]

The stock X445 has a smaller hub diameter than the stock X447, if I'm not mistaken. That's got to be accounted for in the equation somewhere, but I ain't got a clue ???

[siberianhusky]

And a 2x6 is wider than a 2x4, this has gotten stupid! Explain why it matters? Please! This should be good!
I'm done with thread, glad I was able to answer you question Tiqueman.