13x16 or 13x17 RH 1" Bore

81nautique wrote: Now don't go Cajun on me Billy,

I like it!! Alan, now if you can come up with a term for Chris's style it would be great!

Here it is, but you still have to determine the slip before you can use that fancy one otherwise you're just guessing and they always go faster when your're guessing.

fancy Propeller guide

Now don't go Cajun on me Billy, I'm just having a little fun with you.

Edit, I take that back, it works pretty good.

boat dr wrote: Pete just tried to call you , must be still at work. There is a site with the info already there even easier to use.......billy

So is this one of those A & B discusions or would you care to share the web address?

Ok, I don't have Excel on this computer but I do at work so I'll try it there.

8122pbrainard wrote: 81nautique wrote: Pete, were you able to download it and play around with it? No, What program do I use to open it?

It's an excel spreadsheet, it may not be downloadable because of permissions on my server. I think I have your email, I'll send it to you.

8122pbrainard wrote: 81nautique wrote: I spent a few minutes and put together an excel spreadsheet using the formulas from Billy above. It helps you figure out your baseline and then allows you to enter some hypothetical numbers and see what the results would be. Be interesting to hear some opinions and if it is actually helpful. You will have to download it from my FTP site, if you have password problems let me know and I'll email it to you. Prop Guide Alan, Sent it to Tim so he can put all his test results into it. I mentioned a long time ago when he said he was going to do the testing that a % of slip would be a very good indicator of a efficient design prop.

Pete, were you able to download it and play around with it?

This thread hurt my brain.
Lefty

Good info but way too technical, Put the 13x14 oj on it. The stock 351 will turn around 3800-4200 max and go cruising. My bet is he's turning 4300-4600 with the 13x13 as long as it's not trashed.

Barry, I would still borrow a shop tach so you can check the RPM's. Tim (TRbenj) is correct that slip is a difficult factor. The only way to get a semi accurate % is at a steady RPM getting a GPS speed and then calculating backwards. Do get the shop tach hooked up because we would like to know what it's running at.

Go to Delta (one of our sponsers) and look in their used/reconditioned section for a 13x14

It did not copy as well as i wanted but hope this will do..........boat dr

http://continousWave.com:Whaler:Reference:Propeller Calculator

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Propeller Calculator
The propeller calculator computes any one of the five parameters shown below based its relationship to the other four as described below. The calculator is not a Greek Oracle; it simply computes an answer based on your inputs. Prior to clicking the Calculate button, you must have one field blank. You can select the units for the BOAT SPEED parameter. (If units are changed you must force a recalculate.) The calculator returns advisory messages based on your input.



Propeller Calculator v1.1. Written in PERL by James F. Hebert. ENGINE PROPELLER BOAT
Speed Ratio Pitch Slip Speed
RPM :1   in. %   MPH KN KPH
Number of decimal places to show:      

NOTE: Some features require a browser with Style Sheet capability.

Ideas for Use
The most commonly calculated value is BOAT SPEED, based on the other four parameters. Set the SLIP value to zero to see what the maximum speed could be. A typical actual value for SLIP would be in the range of 6-10 percent if the propellor is in good condition and running near the maximum speed at which it was designed to operate.

If accurate observations of boat speed versus engine speed have been made, the propeller SLIP can be deduced. This will allow analysis of the propeller performance. Typically values of SLIP will be at least 6% at wide-open-throttle speeds. At lower speeds slip can be much higher, often 50% or more. Generally SLIP decreases as SPEED increases, typically tapering to less than 10 %. If a negative value for SLIP is calculated, the propeller PITCH was understated. Add one-inch to the PITCH for any propeller with cupped blades.

If the PITCH of the prop is not known, it may be deduced by observing the other parameters and using various values for SLIP in the anticipated range. Probably the best assumptions about SLIP can be made at wide-open-throttle speeds, where it will probably be as low as 10% or lower.

Your engine manual will contain information on the GEAR ratio. Usually it is around 2:1, but it varies with horsepower. For 200-HP engines a ratio of 1.86:1 is common. For smaller horsepower engines, higher ratios are used, more like 2.33:1.

For more information on the relationship between these parameters, read my articles on propellers in the Reference section.

Foundation
The calculator is based on the following relationship:

          RPM     PITCH       
SPEED = ----- X ----- X [ 1- (SLIP/100) ]
        RATIO     C       

Where:

RPM a positive number; the crankcase speed in revolutions-per-minute.
RATIO a positive number; lower unit gear reduction ratio; the number of revolutions of the crankshaft to produce one revolution of the prop shaft.
PITCH a positive number; blade pitch of prop in inches.
SLIP a percentage, 0-100; index of propeller performance.
SPEED a positive number; the boat speed.
C a constant to convert inches-per-minute of revolution to boat speed; for miles-per-hour, 1056; for nautical-miles-per-hour, 1215.2; for kilometers-per-hour, 656. (See below for derivation.)
By manipulating the elements using algebra, any of them can be computed if the others are known. Hence:

                      SPEED X RATIO X C
SLIP = 100 X [ 1 - (-------------------) ]
                      RPM X PITCH


               SPEED X RATIO X C
PITCH = ( -------------------------- )
             RPM X [ 1 - (SLIP/100) ]



             RPM X PITCH X [ 1 - (SLIP/100) ]
RATIO = ( ---------------------------------- )
                     SPEED x C


               SPEED X RATIO X C
RPM = ( ---------------------------- )
            PITCH X [ 1 - (SLIP/100) ]


The constant C is derived from the analysis of the dimensions involved in the calculations. The propeller advance is generally given in INCHES/REVOLUTION and the speed of the propeller rotation is generally given in REVOLUTIONS/MINUTE. The speed of the boat would then be calculated in units of INCHES/MINUTE, an unusual dimension which needs to be converted into something more commonly used for boat speed.

The most common conversion is to MILES/HOUR (MPH), which is derived below:

1 HOUR   12 INCH    5280 FOOT    1056 HOUR INCH     
------- X ------- X --------- = --------------
60 MIN    1 FOOT     1 MILE       1 MIN MILE

Similarly, if the results are desired in NAUTICAL MILES/HOUR (KN):

1 HOUR   12 INCH   6076 FOOT      1215.2 HOUR INCH     
------- X ------- X ----------- = -----------------
60 MIN     1 FOOT   1 NAUT-MILE    1 MIN NAUT-MILE
And if results are desired in KILOMETERS/HOUR (KPH):

1 HOUR   12 INCH   3.28 FOOT   1000 M   656 HOUR INCH     
------- X ------- X --------- X ------ = --------------
60 MIN     1 FOOT   1 METER     1 KM     1 MIN KM
Comments or questions about the prop calculator can be posted in a message thread in the forum reserved for that purpose.

Acknowledgements
The propeller calculator was inspired by a JavaScript version that was created by Gary Polson.

Bhedbloom wrote: TRBenj, The Tach on my southwind is not stock, and after reading the other posts I don't think it is reading correctly. The prop is a federal 13x13 cuped and has a few small dings on it. boat dr, I know for a fact that my H-M motor isn't producing 450HP, and my top speed is around 42-43 mph GPS with the 13x13 federal. Could you post the formula that you use to calculate the information in your previous post? It would be helpful to many here. Thanks!

That would make sense if it werent reading correctly. 42-43 MPH is about right, and I would say youre likely turning ~4400 RPM with that cupped 13x13. Like was previously mentioned, you might pick up a little economy with a 13x14. It would take you a long time to recoup the money in gas savings to justify the expenditure on a new prop, though.

I think the Doc is using a fairly simple formula, and Im not sure its very useful. The pitch of the prop is how far it would turn in one revolution (in inches), so subtract a % for slip, multiply by RPM and convert to MPH. There are several problems with that formula- namely slip % is nearly impossible to calculate accurately if you dont know the boat speed and prop RPM. Prop diameter, cup, rake, and efficiency all factor in, as does hull efficiency.

I would think the prop has been de pitched,try another or have it checked.

The otherside is you got a really hotrod motor maybe a little cup to controll rpms would get ya the extra cruise ya want

Tim, you need this motor in your project boat....
13x13 with a 1:1 tranny @ 5500 rpms with 15% slippage will give him 57.6 MPH.
That H/M must be putting out 450HP to push a 2000 lb. boat that fast.
Or his numbers are all wrong, you do the math.Pitch ,rpm's, ratio,slippage,will give you speed, and I factored in 15% slippage. That is way high even on an old Federal prop.
Something ain't rite here, BS maybe????

5500 seems way high. I didnt think a 351 could push that big a boat that fast, even if it is a H-M. What kind of 13x13 do you have? Are you sure the tach is reading correctly? Whats the top speed (preferably GPS)?

Barry, I'm sorry to say that it doesn't quite work the way you're thinking. The engine will be under a greater load and will burn damn close to the same amount of gas. Plus, beyond a 15 pitch on a inboard type prop, the efficency drops way off due to the prop blade angle. The prop will start throwing more water out the sides (radially) than out the back. With this in mind, you may even get less MPG! You may want to consider just going to a 13x14. What WOT RPM's are you getting?