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suider

Prop Sizing

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Hey guys and gals-

Let me preface this by saying this particular question IS in fact for a powerboat repower, but I know there are a lot of knowledgeable people lurking around here, so I thought I'd at least ask.

Do y'all have a favorite propeller calculating program/algorithm? I'm having a heck of a time using either of my two stand-by methods (Crouch and Bp-δ) because, in this particular case, I NEED to override the optimum diameter- and in the 'abnormal' direction- I need to override UP. SO, I'd like to be able to essentially start with a 'desired' diameter and alter P and possibly DAR to suit. Any thoughts? It's VERY likely easier than I'm making it, but I keep getting mired somewhere.

And, before you ask:

  1. I need to override optimum diameter due to existing shaft size. All of my standard calculations are giving me an optimum D that just isn't possible with the existing shaft size.
  2. No, I can't add a reduction gear due to a lack of space in the boat.
  3. It's a Hackercraft, so we are talking a light boat (24', 4500lbs) with VERY little deadrise (7-8 degrees).
  4. I understand there will be tradeoffs by straying from optimum, but we are likely talking the difference of a few knots at WOT. The customer doesn't care how hard his ears are pinned back, as long as they are. Even with a less than optimum D, the boat will be 40kts+.

Thanks!

 

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Talk to a prop shop.

Way too much bullshit and guessing on the Interweb for a job that expensive.

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Hey Suider , long time , how are u ?

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12 minutes ago, SloopJonB said:

Talk to a prop shop.

Way too much bullshit and guessing on the Interweb for a job that expensive.

I hear you, JonB. And I have. It just seems that most of my 'normal' prop shops (of which I have several) aren't THAT interested in solving issues right now- they'd rather just say 'it can't be done'. And I don't say that to be a jerk- this project went WAY too deep in the off season due to customer indecision and now I'm sure they are just as busy/behind the 8 ball as I am. But your point of interweb prop sizing is well taken- and that wasn't exactly what I was looking for- I was more curious for an alternative to the two methods I usually use.

9 minutes ago, Mid said:

Hey Suider , long time , how are u ?

Hey Mid! I've been back lurking for a while, just don't post as much anymore. Things are good-just busier than they were 'back in the day'!

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(Interested observer - I'm trying to size a prop too but smaller than recommended and get different answers depending on which sites/ formulae/ people I talk to. At least mine will be feathering so I can adjust the pitch if wrong.)

 

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