Prop Blade Mapping

[Charles Perdue]

Blade mapping is just another tool for learning props and is also another method of record keeping of your favorite props and of comparing one blade to the other.

It is a little time consuming but for me it is worth it.

Basicly make a reference drawing of all the blades of the prop (I keep these in a note book) and overlay a grid pattern on the sketch using whatever unit of measurement you are comfortable with. I use 1/10 ths of an inch on the prop and 4/10 ths on the drawing. Mark a grid of the same pattern on the inside of each of the prop blades. I expand the sketch at about a 4:1 ratio to make the drawing easier to read. On areas of the prop that have a large change over a small distance (as in trailing edge cup), I make the grid lines closer together. Set the prop in the pitch gauge and take the measurements at all of the crossing points of the grid lines on the prop. Write these down on the drawing at their corresponding points using the grid pattern on the drawing.

Do all of the blades. When you are finished, you will then have a very accurate visual reference of the pitch progession and transition that happens over the entire area of the prop blades.

After you do a few props, this becomes very easy to do.

Keep good notes of each of the props behavior, that you have blade mapped, with the drawing in the notebook and as you use them, your understanding of what parts of a prop blade has what effects on the tuning of the boat will become a lot easier.

Charles

 

[RodneyPierce]

 

[Mike Larson]

Charles... I have mapped prop sheets from Kevin B that are based on the center line of the hub with some kind of xyz ( machinist guy nomenclature), on them... same deal?.... thing is to me, the more numbers mapped out the harder and more meticulous it is to get the things perfect blade to blade, ie: they drive me nuts..... makes sense to know what you had in a good propellor, though... mike

 

[Charles Perdue]

I am not familiar with KB's prop sheets. This system was hatched many years ago by myself and some other boaters that wanted a better way to compare one prop to another and to try to find out why some props, that were supposed to be the same, worked better than others.

Just another tool though, no better or no worse than the user.

Extremely difficult to get the blades exactly the same.

Charles

 

[hugh hargett]

Tongue "thickness" plays a major part in why two of the seemingly same props may act diferently on a boat. Thats another reason why its important to look at leading edge pitch numbers, thinckness, etc. for propeller consistency.

 

[Charles Perdue]

Tongue thickness or blade thickness plays no part in comparing props as that is part of the first step in prepping a prop, the thinning and balancing. That is the easiest to check, just use your calipers when thinning the blade.

Every part of the prop blade is important, if it were not, leave that part out.

It is the complete package.

 

[hugh hargett]

Okay. So what have you learned from your mappings that were the causes of various inconsistency in seemingly the same s&b propellers? Do you have any photos of your maps that you would share ?

 

[Charles Perdue]

Not for public disclosure.

 

[hugh hargett]

LOL :lol: wasnt looking to disect it Mr. Perdue I just wanted to see it so I can get a idea of exactly what you mean. :lol: :lol:

 

[Charles Perdue]

I gave you the tool, it is up to you to use it.

Mr. Jimmy Gale ( JG Props) was one of the other people that used blade mapping, I do not recall who some of the others were. It was just one of the many boating subjects that were conceived and discussed under the shade trees at Legg Lake on the weekends. A lot of guys would participate. Just some of them were Don Maher, Steve O'Donnell, Jack O'Donnell, Mark Grim, Jack Oxley, Joe Monohan, Ron Russell, Paul Dassonville, Scott Bouchie, Alton Bouchie, Norn Teague, Duff, Larry Ingleson and many,many others. Back then there was no internet to use to discuss and share ideas, the 3 fastest forms of communication were telephone, television and tell-a-woman. A normal play sunday would have 30 to 40 boats at the lake.

 

[dwilfong]

Dick Jones told me about mapping the prop with a grid. I have used the FO gage to do this.

Franks gage is made for just this kind of thing.

Have done a few and have learned that the first 20 deg off the tung mean allot to how fast the prop will go.

Would take a prop that a buddy of mine would do for his gas boat map the lead in and tell him how fast the boat would go.

I was always real close with in a MPH or 2.

Takes time to do but you will learn allot from spending the time.

With franks gage you can keep track of the lift at 5deg intervals. Do this at every 10% out from the hub and you will get a real good picture of the progression and where it is on the prop.

Now knowing what it all means. test test test.

David

 

[hugh hargett]

It seems that abc has introduced a line of propellers that have done away with pitch inconsistencies in the same propellers.

 

[lohring]

A long time ago as a way of measuring existing propellers I used a milling machine with digital readouts. Contact between the propeller and probe is indicated with a continuity tester. Below are pictures of the setup and graphs of raw pitch and rake data. More data points would give greater accuracy.

Lohring Miller