Inboard Propeller sizing / theory ??

Cupping reference

Hello Jehirdman,

Thanks for your cupping reference - it was very useful. Do you have anymore on leading or trailing edge cupping or camber?

Thanks,

nevd

 

No, I just googled that one up, though I am familliar with MacPherson's work. Most propulsor designs are conserative or you throw horsepower at it. Only the real go-fast guys do much prop tweeking.

 

On a planing boat I would only use cupped blades. The shops around here do it as standard practice, have been as long as I can remember. They have always said it added from 1/2 to 1 pitch in load. On my last boat one pitch was 250 RPM. I still think I would simply add cupping to the current props.

 

I am attempting to optimize a prop /tranny combo , and could sure use a recomendation for an on line calculator.

Sure Skeens works , but for me its too much work to run thru all the variables, in an attempt at optimization .

Hopefully,

FAST FRED

 

Fast Fred,

the best one I've found is on the boatdiesel.com site. It's not perfect as it can't really predict differences in speed at cruise vs wot for different blade configurations but other than that, it was more accurate than michigan wheels predictions. You do have to be a member to use it though.

 

Just a little anecdote from the UK. I was involved in hand over trials with a couple of launches that were not coming up to spec speed. Fairly large ie 75ft and 20kts reqd. Engine parameters were all being met . Contacted prop mfrs send them down and we will fix. Took myself met at gates Sat morning! carried both into foundry were placed on large pile os sand designer took off coat hit each blade with very large wooden mallet slightly reducing tip pitch. Returned to trials fitted boats ran up to speed???????

 

Propeller seminar

I'm posting the following for anyone interested in digging deeper into the topic of propeller performance. Don

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SEMINAR NOTICE

Contemporary Propeller Performance and Sizing

This 3rd Annual Propeller Seminar from HydroComp is being held in Naples,
Florida USA on January 21-22. This professional development seminar is
suitable for everyone with an interest in inboard propeller propulsion,
including ship operators, boat owners and builders, propeller dealers and
manufacturers, engine and gear companies, port agents, and surveyors.

One- and two-day tracks are available depending on your particular
interests. The first day is where marine professionals can reacquaint
themselves with the principles of marine propulsion for inboard propellers
on all boat types, from large commercial ships to work boats to smaller
"go-fast" boats. The second day is devoted to propeller sizing calculations
for those actively involved with the selection and installation of marine
propellers.

Complete information can be found at

http://www.hydrocompinc.com/support/2005PropellerSeminar.htm

Thank you.

Regards,

Donald M. MacPherson
VP Technical Director
HydroComp, Inc.

Celebrating 20 years of excellence.

 

Prop companies give you a close GUESS. You need to find a local prop shop or place with used GOOD props close to the GUESS. Borrow one at a time until you are happy. Then add $$ to the deposit you left at the start. Works every time. OR. Have lots of people with a prop you can borrow. There is no other way. Save money and freinds. Make double sure the nut and cotter pin is new each time. Don's Prop shop in Clayton, N Y is setting a used Hi Five aside for me. Rich