Modelling a Propeller

[Roflhat]

Hi,

For folks who don't know me, I'm studying Naval Architecture with high performance marine vehicles at the University of Strathclyde.
For my fourth year project I want to model a surface piercing propeller, namely a through hub cleaver. I have an 11 x 18 pitch Mercury cleaver which I hope to use as the basis of my design. My aim in the future is to design and model my own propellers, but I would like to start by modelling and existing propeller.

My plan is to get the propeller scanned and get as many figures from it as possible so I can model it. I hope to send it to a company in the UK for this. The prop is in very good condition but I'm going to send it to get repaired so it's perfect in order to start with as good a model as i can.

I want to model this propeller using CAD software and possibly modify the design slightly, I want the prop to use a removable hub kit so it can be replaced if damaged or for use on a different engine.

If anyone has any experience on this would be greatly appreciated, I'm expecting a steep learning curve.

Thanks

[zul8tr]

Exactly what are you modeling? With CAD that would just be the geometry. Are you going to model the hydrodynamics with CFD software + experimental data. The air water interface as well as the entrained air water mix is where the complication comes in with surface piercing props (SPP). Here are some articles I came across:

http://www.well.com/~pk/SPAprofboat.html

https://www.navalengineers.org/ProceedingsDocs/FAST2011/FAST_C/C5-3.FAST2011.Scherer_Patil.pdf

[Roflhat]

Thanks for the reply zul8tr,
I've been speaking to a company in the UK who can scan my propeller and provide a parametric model in IGES format, which I could then modify in the software available at Uni.
My initial plan was to carry out a CFD analysis but I've been advised by quite a few people that this is very ambitious, there are a few people in our department doing that for their PHD.

So my plan now is to get a model of the propeller and modify it from there. I think for now I will leave the design of the propeller blades as they are and just modify the hub.
Thanks for the links, I'll give them a read when I get a chance.

[zul8tr]

Keep us informed on your progress.

[Roflhat]

Will do, sure I'll have plenty questions!
I'm planning on changing the hub so it can use a removable hub kit, what would you recommend? I was looking at Ron's hubs or maybe a Rubex kit, so it can be replaced and also used on a variety of motors.

[zul8tr]

Can't help on the hub Q, Ron is a good source for Q's on that. The interchangeable Rubex hub appears to be a good choice for your purpose.

[Fastjeff57]

If you really want to learn about propellers, try making your own and running them. Since I run oddball Mercs (ex: Mark 78 on a Mark 55 tower) I have to build my own props; and it's been...educational. The latest, Prop #5 (photo), is working fairly well, but #4 self-destructed--not enough weld fillet. I actually have a video of its blades blowing off! Oh well...

I beat the blades out of 1/8 stainless plate and weld them to a hub made from common pipe material. (Crude I know, but it works.) The hubs come from Surplus Supply.

Jeff

[Roflhat]

That's really impressive, do you balance them yourself? I was looking at getting a static balancer.
If this project goes well I hope to get a model 3D printed in plastic so I can at least see if it works. There's a lot of exciting technology happening in relation to metal 3D printing, although I think the prices are still huge at the moment.

[zul8tr]

Thanks for the reply zul8tr,
I've been speaking to a company in the UK who can scan my propeller and provide a parametric model in IGES format, which I could then modify in the software available at Uni.
My initial plan was to carry out a CFD analysis but I've been advised by quite a few people that this is very ambitious, there are a few people in our department doing that for their PHD.


So my plan now is to get a model of the propeller and modify it from there. I think for now I will leave the design of the propeller blades as they are and just modify the hub.
Thanks for the links, I'll give them a read when I get a chance.

Once you get the propeller measured what will be your guideline parameters to mod the hub? What is your plan to perform the mods and test to determine the affects of the mod? Will the testing be done in the lab or on a boat in a lake? What will you be measuring to determine the affect of the mod? Have you defined the variables and how you will control them? There are many for the prop + the power source used + the water? I have done lab and field testing and control of variables and what will be measured are key to get reliable results that relate to the mod being done. Do you plan on any statistical analysis of the measured data to determine the reliability (consistency to reproduce results) and significance of the mod results?

[Roflhat]

It's not going to be that complex, we don't have too much time for this project. If I want to go into further detail then it will be in the future and in my own time. All I want to do for this project is change the hub so I can use a removable hub kit, and change the shape of the bits which connect the inner hub to the outer hub, so they are effectively a continuation of the blade (as if you took an over-hub cleaver and changed it to through-hub). This should allow me to modify the same design in the future to create an over-hub propeller from the same model.
I do want to learn more about propellers, but for this project I've been told to keep it relatively simple. I don't have enough experience to be able to modify the design of the propeller itself, so I'm trying to keep it realistic.

[zul8tr]

It's not going to be that complex, we don't have too much time for this project. If I want to go into further detail then it will be in the future and in my own time. All I want to do for this project is change the hub so I can use a removable hub kit, and change the shape of the bits which connect the inner hub to the outer hub, so they are effectively a continuation of the blade (as if you took an over-hub cleaver and changed it to through-hub). This should allow me to modify the same design in the future to create an over-hub propeller from the same model.
I do want to learn more about propellers, but for this project I've been told to keep it relatively simple. I don't have enough experience to be able to modify the design of the propeller itself, so I'm trying to keep it realistic.

That is a good approach since you were told to keep it simple. Keep us informed.

[Fastjeff57]

...(On my homemade props) "...do you balance them yourself?"

I spin balance them in the fashion of a ceiling fan! (Crude but effective.) Each blade is carefully weighed before welding with a digital scale and 'adjusted' until they are equal.

Jeff

[Roflhat]

update on this, sent the propeller away, 11x18p Mercury Cleaver. Got the IGES file back a few days ago, here's a couple screenshots from Rhino
http://i1013.photobucket.com/albums/af256/Roflhat/IMG_0123.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_0123.jpg.html)

http://i1013.photobucket.com/albums/af256/Roflhat/IMG_0124.jpg (http://s1013.photobucket.com/user/Roflhat/media/IMG_0124.jpg.html)

I've bought a 13 spline RUBEX hub which I'm going to use as a reference to model around, I'll start modifying the design hopefully towards the end of January

[zul8tr]

That looks like a progressive pitch prop based on the curveed blade section with high rake. Now that you have the 3D digital file you can (I suppose) take a radial cut thru the blades at a given radius to see the 3 blade foil x-sections. Then calculate the pitch on the thrust side of the blade from lead to trail edge along that radial cut. Do that for numerous radii and plot the results and get a contour map of pitch at all points measured. It will show you the accuracy of blade manufacturer (generally not the same). Total average blade pitch can then be determined with contour area averaging of all blades. Then you have a record of what you started with.

In case you do not know it, at any point on blade thrust surface: Pitch = 2 x PI x R x Tan(Angle)
PI = 3.14159....
R = radius from hub shaft center (inches for pitch in inches)
Angle = measured at 90 degrees to pitch point interested in on the blade thrust side cut of the foil x-section rearward to a line parallel to prop shaft centerline. The angle is measured in the same plane as the radial cut was made (geometrically, the plane is at 90 degrees to the foil x-section cut and tangent at the pitch point interested in).

[zul8tr]

OK but at least you have the digital file for the future.

[Roflhat]

Thanks zul8tr, that's all good information. I'm looking for literature on this, do you know of any good books regarding propeller design? I'm hoping to get Marine Propellers and Propulsion by John Carlton from the University library.

[zul8tr]

Here are some links I have collected discussing props. Note the pitch gage and the angle measured on the blade relative to the prop shaft centerline at a given radius. That is what the formula above represents.

http://www.boatracingfacts.com/forums/showthread.php?41-Progressive-Pitch

http://www.boatracingfacts.com/forums/showthread.php?10451-LH-and-RT-Pitch-Gauge-by-Hill-Marine&highlight=pitch+gage

http://www.vicprop.com/propeller101.htm#7

http://www.screamandfly.com/showthread.php?24877-Polish-prop-or-not

I have this book by Dave Geer and is a good reference on propellor basics

http://www.amazon.ca/The-Propeller-Handbook-Installing-Understanding/dp/0071381767

Jim Russel has a book on propeller design. He has a lot of great info on this site

http://tunnelboats.com/secretsofpropellerdesign.html

[Roflhat]

I'm just starting on this now, anyone have any advice regarding extrapolating the blade shape further into the hub? I want to remove the fillet where the blade joins the outside of the hub and move it inside the exhaust tube, with the blade continuing through.
Here's a photo of a propeller which looks like what I'm aiming for.
http://www.mccauleyandson.com/lightbox2.05/images/roddyforeman16_800.jpg

[Fastjeff57]

I did that to one my props, whose hub is smaller in diameter than the 'bullet'. Thought it would reduce some nasty cavitation I was getting on plane off. (My boat was used to take grand kiddies for rides--you don't want to hang over the bow with them aboard to get on plane!) The 'barrel' really didn't help, so I removed in and lived with the cavitation.

Jeff

PS: Lots of folks, with 'jet prop' exhausts, use a prop with non-jet prop type hub. The motor will over-rev a bit on plane off, due to exhaust-caused cavitation, but that goes away soon as you get on top. (I'm sure you already knew this!) Your prop could dispense with the outer hub completely.

[Roflhat]

Yeh, I'm thinking with this design the exhaust hub will be structurally redundant, so to turn it into and over-hub exhaust prop you could simply remove the exhaust hub.
But for this project I want to keep the exhaust hub, but just make the blade shape like the photo posted above. I figure this will increase the effective blade area, as the fillet between the blade and the hub is moved to inside the exhaust hub.

[Ron Hill]

I made some props like this about 30 years ago, we weld stainless tubing over the blades as the rules require thru hub exhaust. If you don't have to run a thruu hub these over hubs are fast.


I'm just starting on this now, anyone have any advice regarding extrapolating the blade shape further into the hub? I want to remove the fillet where the blade joins the outside of the hub and move it inside the exhaust tube, with the blade continuing through.
Here's a photo of a propeller which looks like what I'm aiming for.
http://www.mccauleyandson.com/lightbox2.05/images/roddyforeman16_800.jpg

[Roflhat]

I found that photo on http://www.mccauleyandson.com/html/what.html
I've spoken to Joe McCauleuy, who reflects what you say Ron - these props worked well when through hub exhaust is required. I figure they should be faster than an equivelent through-hub cleaver

[zul8tr]

I made some props like this about 30 years ago, we weld stainless tubing over the blades as the rules require thru hub exhaust. If you don't have to run a thruu hub these over hubs are fast.

Ron

On the 3 blade cleaver prop 3rd picture, what is your theory for the offset trailing edge from the shaft center, unlike the 2nd picture where the trailing edge alignment of the 3 cleaver blades intersect at the shaft center?

[Roflhat]

I'm looking to get a 3D model printed once I've finished my design, anyone have any knowledge on different forms of plastic? Generally available ones are ABS, PLA and Nylon. Looking at ProPulse props it seems they chose Nylon, although it is fibreglass reinforced.

[Per]

I suggest you use ABS. PLA pretty much s*cks to machine or shape. Been there done that, had to get new part made of ABS. Have no experience from printed nylon parts. don´t expect to use a printed propp for anyting but mock-up. IF you don´t use a Titanium printer that is:)

[mathrich]

I'm looking to get a 3D model printed once I've finished my design, anyone have any knowledge on different forms of plastic? Generally available ones are ABS, PLA and Nylon. Looking at ProPulse props it seems they chose Nylon, although it is fibreglass reinforced.

If you print with ABS you run a greater risk of the part warping(depending on the competency of the person running the printer). A possible idea is to print it in PLA then cast it. If you print in PLA, mold around it with plaster or sand, heat the mold so all the PLA melts out, then cast it you can obtain pretty good results. The same process can be done with ABS you just need to get the mold hotter than for PLA.

http://3dtopo.com/lostPLA/

[Roflhat]

Thanks for the replies, I'll probably just get one printed in ABS for show. I was looking at metal additive printing but the prices are still very high.

mathrich - thanks for the link, very interesting stuff. Think I'll look into that some more once the project is done

[hOoTs]

I have 4 or 5 old 2 blade yamoto props. Not the brass ones. They are stainless.If you would like to mess with them you can have them.

[mathrich]

I'm not the op but I could use one. (: I'd like to try and print then cast a propeller like I described above. It would be nice to have a real race propeller to design off of.

[Roflhat]

I have 4 or 5 old 2 blade yamoto props. Not the brass ones. They are stainless.If you would like to mess with them you can have them.

I would certainly appreciate that thank you! I'll send you a PM

If mathrich wants a one or two maybe we can split them?

[hOoTs]

I responded to your PM. Let me know if you got it?

[Roflhat]

I responded to your PM. Let me know if you got it?

Got it thanks - sent a reply

[hOoTs]

Ok I got the props for you guys. mathrich I have my old OSY 400 2 blade,and a 3 blade that through an ear off. He was leading at the worlds finals when it broke. Roflhat I got you 3 blade cleaver that will work on your D stock. And one 2 blade. PM me your address and I'll send them to you.

[Roflhat]

Ok I got the props for you guys. mathrich I have my old OSY 400 2 blade,and a 3 blade that through an ear off. He was leading at the worlds finals when it broke. Roflhat I got you 3 blade cleaver that will work on your D stock. And one 2 blade. PM me your address and I'll send them to you.

Fantastic, thank you very much! sent you a PM

[Roflhat]

Regarding material, does anyone have any experience with Aluminium Bronze/NiBrAl? Seems a lot of companies prefer to offer this for casting as opposed to stainless. The strength and hardness figures seem comparable to those of stainless steel, and the propeller would be 200 grams lighter in NiBrAl - 2kg instead of 2.2kg.
Also on the Rolla site as well as others, it seems propellers for larger applications use NiBrAl.

[hOoTs]

RJ just told me that it will bend

[Roflhat]

RJ just told me that it will bend

Thanks Tim,
Seems to be the general consensus - not as stiff as stainless but better than brass.

[hOoTs]

You guys ever think about doing something like this? http://piranha.com/