propeller software

[lifetime]

hello!
Is there anyone who knows about Propeller Calculation Software..Or how to calculate correct dimensions of a propeller??

[Eric Sponberg]

Lifetime,

The best propeller calculations come from propeller charts such as Bp-delta charts or Kt-Kq-J charts, which are all based on open water model tests of different kinds of propellers. I use NavCad from HydroComp (www.hydrocompinc.com) which is a very comprehensive program (and pretty expensive) for specifying propellers that operates on a PC. The program allows you to model hull resistance in any number of methods for many different kinds of craft--sailboats, powerboats, tugs, ships, barges, etc. You can also import your own model test results for vessel resistance. You can import engine power, torque, and fuel consumption curves for any kind of engine. First you determine the vessel resistance for the range of speeds you want, then you determine which engine you want (put in its power curve) and then start the propeller calculations to determine diameter and pitch. You can even specify the amount of cupping. The program also works for waterjets. The program has many Kt-Kq-J curves within its database for many different manufacturers of propellers from around the world. All of the results are saved in a spreadsheet format and you can chart any variable against any other variable. You can also export to another spreadsheet if you want, and plot reports. It's a really neat program.

If you don't want to spend the few thousand dollars for the program, I highly recommend Dave Gerr's book, the Propeller Handbook. I have found it to give very good results with simple hand calculations and the charts within it. The Bp-delta method is the one I use for preliminary calculations. The book fully explains the science behind propeller physics in a pretty simple format. I don't know of any other program available that gives provides the simple calculations that this book has, but if you can understand what the book gives you, you can probably write spreadsheets yourself for your own needs.

Eric

[DaveB]

I've found this one to be pretty handy:

http://www-personal.engin.umich.edu/...b/propelle.htm

Cheers,

Dave

p.s. there's some other neat stuff at:

http://www-personal.engin.umich.edu/...re_manuals.htm

[CGN]

Another good alternative is

http://www.sea-power.net/ very complete software for resistance and propeller selection

And Eric is right, Dave Gerr book is a very good reference, highly recommended

[DMacPherson]

Let me chime in here, if I may...

First, thanks Eric for the kind words about NavCad. It was a pretty good overwiew of its capabilities. As you know, we've been developing NavCad since 1984, and it has become the de-facto powering tool for naval architects. (I believe we hit 500 users this year.)

For those who do not need the broad capabilities of NavCad, we do offer less expensive softwre - all derived from the technical features of NavCad. There is SwiftCraft, a speed-power tool for small ships using conventional propellers (serving most of what boat and yacht designers will need). For just propeller sizing, there is PropExpert, which is used by over 150 propeller and engine companies and their dealer/distributor network.

I also agree that The Propeller Handbook is a good primer. However, it does make a couple of recommendations with respect to propeller sizing that I find significantly in error. For example, there is a comment about using a reduced RPM for the propeller design point. If you follow this practice, you will choose a propeller which will be overloaded in service (too much pitch). There are other such things, but overall it is a very good reference - just be careful about using it to size propellers, and always get a professional "second opinion" (whether that be with validated software, a trained prop shop or a consultant). Propellers are not cheap, and buying one back costs much more than having it done right.

Regards,

Don MacPherson
Tech Dir
HydroComp

[CDBarry]

Also, using the B-series data (including the Bp-delta charts in Gerr) results in overpitching if used for segmental props. The hydrodynamic pitch of a Troost or B prop is slightly less than its nominal pitch compared to a segmental one, so a segmental prop sized off B charts will typically be about 5% under RPM at WOT. Since the standard is 2-3% over, this might be a problem.

Don's other point is a very good practical one, since most prop shops will take back a bad prop for free if they sized it, but not if you did.

Finally, having software that actually lets you see in detail what is going on with torque, turns, etc. and lets you play with it is very valuable for really diagnosing problems or making a match for best service.