Is there a systematic way to balance a prop

Hi there, I could not get a prop which turns in opposite direction as the first one. I had to make my own props, simple one's, just for the 3 to 5 knots my boat is moving. For my first motor I made a large prop and this was easier to balance than smaller props at higher speed.
My first step was. to weigh the blades and made sure they had the same weight.
The second step I took, was to turn them on two very light ball bearings to see whether the stopping point is always at the same position. If so, I had to change the balance weight, that works quite well.
The third step was, I tried to ensure that all 3 blades does not wobble, by having a parallel plate, which would show any discrepancy between plate space and tip of the prop.

Any other suggestion I could try out, to make the props working as optimum as possible.
Many thanks
Bert

 

A two blade prop is going to be the way to go for 3 - 5 knots.
Model airplane propellers work very well and come balanced.

 

You also need to balance the pitch.
Gauging Propellers http://www.rundquist.com/how_check_pitch.htm

 

Thank you Bluebell, but I made the 3 blade already, I may as well finished and see how it works. Thanks for your thoughts.
bert

Thanks Gonzo, It gives me some directions. I enlarged the photo and it does give me a good idea, on how to construct something similar.
Bert

 

It is not hard to build for a handy guy like you. In the future it can be used for repairs too.

 

Can you really make an efficient prop? Baumann Marine modifies mine and they have all kinds of jigs and equipment. If the prop is not exactly balanced it's going to be really inefficient. I had one shop add a bit of cup and they didn't do it exactly balanced, boat felt like I was riding a wild horse.

I would just get them to make one for you.

Repairs
STANDARD REPAIR PROCEDURES

All propellers are repaired as close to OEM standards as possible. Pitch and Rake are set back using pitch blocks, when available, giving an exact pitch and rake setting for each blade. When pitch blocks are NOT available, pitch and rake is set by hand using Baumann’s own pitch gauges to measure settings to the nearest degree. This type of workmanship is what sets us apart from other propeller shops. Three generations of craftsmanship are put into every hand pitched propeller.

After pitch and rake are set to OEM standards, the blades are measured for correct diameter. Baumann Propellers has a standard of rebuilding every propeller to original size, unless the customer gives specific instructions. Simply trimming the edges on simple repairs could seriously affect the performance of your boat, as well as shorter the life of your propeller.

The welded propeller is then ground down and sanded to the original blade shape and size. Edges on the leading edges are left rounded, not squared off, to give a more efficient entry. All propellers requiring cup are now cupped back to OEM specifications or as requested.

Every propeller is then static balanced to a zero tolerance to ensure the smoothest performance possible. This also greatly reduces the chance of the propeller causing damage to the lower unit, due to vibration.

The last procedure of repair is finishing. If the propeller is a painted propeller upon arrival, it is repainted back to factory color. If the propeller has a felt finish or a high polish finish, it is the cleaned accordingly. After the polishing process, the propeller is rechecked to ensure a precision balance.

Baumann Propellers is also able to do more advanced repairs for your propellers. Complete blade replacements, tip replacements, Changing more than two inches of pitch, are all common repairs and are accomplished easily in shop.

We also replace hubs for just about every prop available. Most propellers requiring hub replacement only can be taken care of while the customer waits. Thus saving you both time and money.

Baumann Propellers provides numerous other services for propellers, rudders, shafts, couplings, struts, and other marine related hardware. If you have any questions, please call or e-mail us and we will be glad to answer your question.

 

Thank you Jorgepeace, I am sure that the first propeller Bauman has made, was also not 100% efficient either. He learned from making it better and better. That is true, for anything one is making. Thank you for your reply, everything, all information helps to do it right. Thanks
Bert

 

That is what I always say too, good luck! ... BTW, why do you need counter rotating props for 3-4 knots speed boat?

 

Very simple Jorgepease, I bought 4 brush less motors 1 - 3 Kw (max 6 Kw) 6 years ago.

I modified them with 3 sensors per motor . One of them I used in my first design, with a big heavy reduction gear of 4:1 . I made a mistake and it was metal on metal and it is noisy. But thought, after I cool the motor in transformer oil and it is running under the water surface, the noise would be not noticeable. One learn only from the errors made. Although it works like a dream. I can't complain. I am now busy to use 2 other motors and build them on each side of the wooden rudder I made. In such a way that when I am sailing and use the sail, I can lift the 2 very close to each other motors. That is the reason why I need to turn them opposite each other. I build 2 ESC controllers and can thus manipulate speed and direction interdependently .
Bert

 

I guess you have the balancing part down, but in case you don't I'll post a few RC prop balancing sites. The main thing I can see for sensitivity is to have ends of the shaft the prop is mounted on for balancing as small as possible. That gives the maximum leverage to overcome bearing friction. So if you have a 1" shaft diameter, you'd use a bushing in the prop that would let you use a much smaller shaft, say a 1/8" shaft in 1/8" bearings. With theses RC props, they reduce the size of the shaft and hang the works between magnets. If you can replicate that, it's hard to imagine a better way.

Balancing would be the last step. First would be construction that emphasizes uniformity, such as a jig to correctly hold the blades in position for welding, welding practices that minimize distortion etc. When done with that, I would mount it on a fixed shaft, and slowly rotate it around past a fixed grinding wheel or a fixed belt sander to get the outside radius uniform. Such as mount it on your boat motor and rotate it by hand past a belt sander clamped to a sawhorse or something. Do a little, move the sander in, do a little more etc until they are all ground down the same. If you cut the blade ends close to the correct radius before welding them to the hub, it wouldn't take very much grinding to get them completely uniform as far as length and end shape of the blades.

A method to the madness: How to balance 3 bladed props - RC Groups https://www.rcgroups.com/forums/showthread.php?1578080-A-method-to-the-madness-How-to-balance-3-bladed-props

(The above and below are two different sites)



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Thanks very much that are two very useful video's and the first video example is easy to make. I still, have lots of earth magnets and have a lathe. Very useful thread. Thanks so much. Bert

 

I deleted the vibration meter thing as farting around near a full speed propeller doesn't seem like a good idea. Here's an apparently regular prop balance machine at work. I guess the combination of discs supplies the leverage giving the sensitivity.

 

I would suggest you install the propeller in the rudder ( perhaps even the entire motor, depending on diameter ).
It's called a live rudder and if you can swing 180 degrees of travel in your rudder-post, you've got incredible manoeuvrability!
I've driven 20 foot Duffy's from Newport Beach California, they are set up like this.
For light loads, plastic, model-airplane props are the way to go my friend.
Get rid of the reverse pitch issue by rewiring your set-up, or simply make it a puller prop from the front of the rudder!

 

No Bluebell, I am not so lucky. The angle is maximum 90 degrees and the rudder moves between the two transom extension I made. I agree with you that model-airplane props are the way to go, but I made the 2 smaller props already and am busy to balance them. They are directly mounted on the 12 mm hardened steel shaft of the 2 identical motors. The prop diameter is only 172 mm large (6,77 inch) If it does not work satisfactory, I will make something else. Thanks Bert

 

Thank you SamSam, great information, very useful and not so difficult to make something like that. Thanks. Bert