# Savitsky Power Prediction

Discussion in 'Software' started by guest12020101217, Sep 23, 2003.

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### arkieNew Member

Shaft angle effect

Hi all,

I’m using Savitsky method in my software in a simplified form with fixed VCG and f parameters. Recently I decided to add variable VCG and shaft inclination to simulate outboard motor trimming. I was very much surprised that the model is practically insensitive to the shaft angle variation. The pictures below show two cases of +5 deg and -15 deg inclination (f=0.372 and f=0.966 m respectively). Speed is equal in both cases, trim and wetted area differ very slightly. It is contrary to my own practical experience and common practice. Even smaller change in angle led to change in RPM of at least 200 and more notable trim, wetted area/splash pattern change.
I checked formulas, code e.t.c., everything was OK. Running sample from original Savitsky’s paper gives good agreement. I checked this trim vs angle reaction in FreeShip software and had same small changes. What’s wrong?

My other sample data in terms of Savitsky-64 was as follows (metric, sorry):
Delta=365 kg
LCG=1.47 m
VCG=0.268 m
b=1.38 m
Beta=9.4 deg.

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### MothilalNew Member

xxx

Hii Dingo,

I have seen your planning spreadsheet. I have found that it's very useful for calculation part. But, i was week in coding part and i am unable to get the coding you have done in VBA. Can i get a brief on this coding.

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### MothilalNew Member

xxx

Dear Dingo,

1) I have Calculated Trim angle by using your Spreadsheet but it shows trim angle is less in high Speed and High at Low Speed. From Conceptual Point of View trim angle should be more at High Speed. Am I right?

2) To calculate trim angle you have done coding in Excel. Can i know brief on this coding how you have done. What exactly is happening in this coding(Bereken Trim).

3) In my boat i am having waterjet system. what is the effect of this system on resistance and propulsion.

4)My Email Id: mothilal.iitkgp@gmail.com. Please send me if your having any info on the above queries.

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### rxcompositeSenior Member

Mothilal-The only code written is to automate it otherwise the formulae is shown in the cells.

If you are using waterjet, Arneson software might work for you as the principle is similar. It is a modified short form Savitsky. Don't have the link but it was mentioned several times in this forum, including the history and note from the author. it won't work in newer PC. Mine does in Pentium 4 and windows 98.

Ah yes! Search Daiquiri's posts. It was a long time ago. There is a link.

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### daiquiriEngineering and Design

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### daiquiriEngineering and Design

Anyways, Arkie, it is true what you have noticed - the thrust angle is not accounted for in the Savitsky's formulae, although it does appear (the variable "epsilon") in the drawings shown in his papers.

A good occasion to extend the calculation method by including the epsilon too, isn't it?

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### rxcompositeSenior Member

Memories just pop in my head sometimes especially with what you have posted. Mine worked when I was using windows and floppy discs. Later version gave me just a tiny window image and I don't know why? Maybe because I saved it on a hard disc. Can't open it now as I am using Win 7, 64bit format. Used to have it full screen in old windows.

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### SukiSoloSenior Member

You might need to specify 32 bit for the application, if it ran on NT and NTFS. Win 98 had both 16 and 32 bit code along with the file formats FAT16 and FAT32. DosBox runs on Win 7, though I've stuck to the 32 bit version (of 7), but do have the 64 bit as well, partly to deal with legacy software.
Even have a Win95/98 Pentium 2 400 still running fine with original CR2032 battery! There are/were apps that would work on Win 95 but not on 98 despite claiming to be compatible. That would be 3rd edition Win95.

Still have to decide whether to go to Win10? free for a few more days...

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### baeckmoHydrodynamics

What is your recommendation on this, Suki? (sorry taking it a bit off topic!)

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### TANSLSenior Member

My opinion, if you will allow me (I'm not a computer but I make my living with a PC): If everything works well you do not change your OS. When some, important to you, software requires, inevitably, other OS, switch.
Many people regret change only, not to be obsolete. We must learn to give up what we do not need.

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### daiquiriEngineering and Design

IMO, there is a good offer of refitted PCs with old operative systems around, like the one in my previous post. If a given old software is important for you, \$50 for a such machine might be a reasonable way.

About Win10 - I am using it and it is a very good, fast and stable OS. A huge quality lap from Win8. It also has a choice of compatibility modes for running older software, for example those made for Win XP.

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### TANSLSenior Member

All programs developed in previous operating systems can run on Windows 10. The reverse is not true. Another thing is the many adventures that one can suffer for proper installation of a program.

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### daiquiriEngineering and Design

But this one won't run on Windows 10.

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### TANSLSenior Member

What I think is that it is not it can not run on W10, but it is difficult to get. Although, I repeat, all programs can run on W10 (even those developed for MS-DOS are supported), the installation and start-up, in some cases, is more complicated than what a normal user can do.

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### rxcompositeSenior Member

Good idea. I just recently fixed my P4 last month. Replaced a few bloated capacitors on the motherboard and it sprang back to life. These dinosaurs just refuses to die. I dusted it and scrubbed clean everything (non electronic) just to preserve it but now you gave me an idea. I am going to put all my old programs in it that came in the floppy disc. I used Arneson only in 1995-96. Never found a use for it afterwards.

We installed W10 a few weeks ago. Works great, no bugs but the more experienced users says we have to upgrade our other apps (like Corel) as there is a conflict. Bugger. More expenses.

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