Prop Pitch Question about DAH racing props

[Krazymaan]

I was told this prop was pounded out by DAH for my STV. The original owner Mark Tabara Racing said it was some sort of yamaha cut, half breed clever concoction. What does he mean by this? He also didn't know the pitch. He said for sure it somewhere near or past a 30 pitch.
What pitch does it look like to your educated eyes? I believe its cupped and something else he said. Anyone know by just looking at it?
It grabs good, pulls hard and will take me to 100 pretty quick, then I chicken out because there seems to be a lot more and I don't need to know where to top end is quite yet.
He said he has $1100 into this prop and I should treat it like gold.
Is there an easy way to figure out the pitch? I watched some dude try to show how on youboob. But that involved printing paper, using a protractor and a right angle square and all sorts of things that I don't remember how to use anymore.
there is no pitch or serial numbers on the prop.
thanks for the help.

[CNC_Guy]

Probably had the leading edges rolled for more bite out of the hole. That's 1 of the standard things they do there. Pics aren't quite big enough to see much on my phone. Do you have a Yammi drag to compare it to?

[Krazymaan]

No I don't have anything to compare too. I don't have another prop. So If I were to buy a second prop to see how and/or if it's better than this one. I might have a starting point. Seems clevers are popular but that don't mean they are good for my boat. I also don't want 4k in props while trying to find my magical prop. So I'd I can figure out exactly what I have that would be helpful.

[CNC_Guy]

He might mean it is a Yammi clone, if you ever go to Lakeville I could meet you after work and you could compare it to a worked and stock yammi drag.

[90 5.0]

No I don't have anything to compare too. I don't have another prop. So If I were to buy a second prop to see how and/or if it's better than this one. I might have a starting point. Seems clevers are popular but that don't mean they are good for my boat. I also don't want 4k in props while trying to find my magical prop. So I'd I can figure out exactly what I have that would be helpful.

If you are trying to find the perfect magic prop as you put it and only spend 4k on your quest consider yourself Lucky

[97 TWISTER]

What kinda RPM's are you turning at 100? Prop slip calculator should help you get in ballpark of pitch. Come checkout a UMPBA race next season and I will let you run some different props of mine. I have yami's 20 thru 28 and some other pretty wicked one's. That sounds like an awesome prop for you " It grabs good, pulls hard and will take me to 100 pretty quick", most guys would kill for a prop like that.

[HStream1]

If John and Jeff Janaky worked that prop there should be a number stamped/etched on it also. Find that number and call DAH ((262) 534-4440). They can give you the complete history on it.

[Krazymaan]

He might mean it is a Yammi clone, if you ever go to Lakeville I could meet you after work and you could compare it to a worked and stock yammi drag.

Maybe I'll take you up on that this weekend. I'm gonna be juggling boats around at my storage pole barn and will be driving by a few times.
Jeff

[Krazymaan]

What kinda RPM's are you turning at 100? Prop slip calculator should help you get in ballpark of pitch. Come checkout a UMPBA race next season and I will let you run some different props of mine. I have yami's 20 thru 28 and some other pretty wicked one's. That sounds like an awesome prop for you " It grabs good, pulls hard and will take me to 100 pretty quick", most guys would kill for a prop like that.

At 63 - 6400 we were going 97 on the river with gps. I don't know how to calculate slip. That was with three of us in the boat. It would still pull your head back when throttling it harder. It has another 2 - 2500 RPMs left in it. Not sure if I want to go that fast. I'm not set up for survival if it wanted to go airborne. I asked Mark Tabara at Tabara Racing how fast he had it. He said 128. It used to be his boat. This is also why I am trying to find out what prop this is. Mark don't even remember. He has tons of props for his F1's and 3's and its been too long.

[HStream1]

There are prop slip calculators out there just google them. but I prefer this formula. Its always been spot on.

RPM X Prop Pitch =
1052 X ratio =

Example: 6400 X 30 = 192000 = 97.228 Theoretical MPH.
---------1056 x 1.87 = 1974.72

All props have slip what percentage can differ from prop to prop. Take theoretical MPH - actual MPH equals % prop slip. EX: 97 - 92 = 5% slip

Im going to take a stab at your prop and guess its 32 Pitch with around 6% slip. Or it could be a 30 with cup (a tall 30 i.e. 31) with 4% slip.

At 63 - 6400 we were going 97 on the river with gps. I don't know how to calculate slip. That was with three of us in the boat. It would still pull your head back when throttling it harder. It has another 2 - 2500 RPMs left in it. Not sure if I want to go that fast. I'm not set up for survival if it wanted to go airborne. I asked Mark Tabara at Tabara Racing how fast he had it. He said 128. It used to be his boat.

[ZUL8TR]

There are prop slip calculators out there just google them. but I prefer this formula. Its always been spot on.

RPM X Prop Pitch =
1052 X ratio =

Example: 6400 X 30 = 192000 = 97.228 Theoretical MPH.
---------1056 x 1.87 = 1974.72

All props have slip what percentage can differ from prop to prop. Take theoretical MPH - actual MPH equals % prop slip. EX: 97 - 92 = 5% slip

Im going to take a stab at your prop and guess its 32 Pitch with around 6% slip. Or it could be a 30 with cup (a tall 30 i.e. 31) with 4% slip.

Actually % Slip = 100 x (MPH theoretical - MPH actual)/MPH theoretical. Based on your example slip = 100x (97-92)/97 = 5.2% not much diff than 5% but not accurate for other speeds.

Example: 6000 rpm 2:1 gear, 18 pitch speed theoretical = 51 mph, At 8% slip actual speed = 47mph. Your calculation method would be 4% slip.about 1/2 of actual.

Example Calculated below:

http://www.mercuryracing.com/prop-slip-calculator/

They use the classic helical screw advance fully submerged prop formula :

Speed (mph) = (1 - slip) x [(pitch x rpm/(1056 x Gear ratio)]

Unfortunately Speed and Slip are rounded to nearest whole number, use actual formula for more decimals
Pitch in inches
Gear ratio decimal = prop gear teeth / drive gear teeth, or one rev of flywheel / rev of prop.
Slip in %

Formula works reasonably well for surface pierce props.

[HStream1]

There is NO prop that has a constant slip % at different speeds. And Im not following where 97-92 = 5.2% If you take the literal formula example that 97.228 Theoretical - 92 actual then yes its 5.2%.

The problem with most all online Prop calculators is you have to plug in a slip percentage to get a answer. And one cant determine the actual slip unless they have a known actual speed.

If one will Calculate Theoretical speed at say 2k, 3k, 4k >>>>> etc. The % slip will change (hopefully lessen) as the RPM's increase and the prop starts to hook up.

Actually % Slip = 100 x (MPH theoretical - MPH actual)/MPH theoretical. Based on your example slip = 100x (97-92)/97 = 5.2% not much diff than 5% but not accurate for other speeds.

Example: 6000 rpm 2:1 gear, 18 pitch speed theoretical = 51 mph, At 8% slip actual speed = 47mph. Your calculation method would be 4% slip.about 1/2 of actual.

Example Calculated below:

http://www.mercuryracing.com/prop-slip-calculator/

They use the classic helical screw advance fully submerged prop formula :

Speed (mph) = (1 - slip) x [(pitch x rpm/(1056 x Gear ratio)]

Unfortunately Speed and Slip are rounded to nearest whole number, use actual formula for more decimals
Pitch in inches
Gear ratio decimal a prop gear/ drive gear teeth
Slip in %

Formula works reasonably well for surface pierce props.

[ZUL8TR]

From my 1st line 5.2% is calculated based on the 97 and the 92 mph speeds you posted, slip = 100(97-92)/97 = 5.2%.
It is not a simple subtraction as you state is all I was posting, the calculation is a simple relative proportion see link.

http://www.go-fast.com/Prop_Slip_Calculator.htm

If you calculated theoretical 97.228 mph then what is the accuracy of the 92 mph you are using to calculate slip. If you are calculating theoretical to 3 decimal places than measured must be to the same decimal places. In field practice math degree of accuracy is rounded to the least number of decimal places or the result is given greater accuracy than can exist.

?NEVER said slip was constant? And I realize slip changes thru the rpm range. The the simple screw formula is for a specific set of conditions of pitch, rpm and gear ratio.

The calculation for slip assuming you have calculated speed with slip = 0 (theoretical) and a measured speed (with same degree of accuracy) then slip can be calculated for the same rpm in both cases for those conditions. Then slip is calculated as I noted by

100(speed theoretical - speed actual)/speed theoretical

All props slip some or there would be no thrust, nature rules.

Here is something else to ponder, what accurate pitch is used for a variable pitch blade with leading edge pitch less than trailing pitch edge pitch (not including cup) at a given radius? The pitch generally used is what is posted on the prop but that is traditionally based on a specific radius but where along the radius? Thus the formula for speed can only be approximate since pitch is approximate. I have experienced cases where speed exceeded the theoretical formula because of variable pitch blades.

Therefore I only use the formula as a relative reference to approximately determine differences not absolute speeds and slip.
As for real world absolute speeds I use a not too long measured distance and a stop watch and compare for different set ups that tells me more than any formulas.

[FORBESAUTO]

All that's fine and dandy as long as you 100 % know exact pitch of prop which rarely do. I had a DAH 27 Srx that calculated at 14% slip which is worse than any prop I ran yet was the fastest prop I ran. It had a rolled leading edge which gave it a progressive pitch which threw a monkey wrench in slip calculations.

[XstreamVking]

Not to mention that most props have a slightly dif pitch for each blade and work real well in spite of it.