# Savitsky Power Prediction

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

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### guest12020101217Junior Member

Hi all

I am writing a savitsky planing power prediction porgram in Mircosoft excel at the moment. Well in fact l am writing two! One using the thoery in principles of yacht design and the other from copies of savitsky's and others papers.

Can anybody tell me how l can get Excel to solve equations like the one below. I need to solve for CLo.

CLb = CLo - 0.0065*B*CLo^0.6

CLb = Deadrise Lift Coefficient
CLo = Flat Plate lift Coefficient
B = deadrise angle.

I can do it by getting excel to plots graphs and me having to pick the value off and enter it in, but l really want excel to solve it.

I want to do the same when solving for the wetted length/wetted beam ratio (L).

CLo =t^1.1 x {0.012L^0.5 + (0.0055L^(5/2))/Cv^2}

t=running trim
L=wetted length/wetted beam ratio
Cv= Speed coefficient

Plan to develop the programs over time and use Maxsurf's Hullspeed as base data. May but the program on net when happy with it.

Any help or comments are very welcome.

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### DimSenior Member

all input data - "from my mind". Check formulas, please.

#### Attached Files:

• ###### colin.xls
File size:
13.5 KB
Views:
3,846
3. Joined: May 2003
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### guest12020101217Junior Member

To Dim

Thanks for your help, but think l didn't explain what l needed help on clearly. Need excel to find CLo from a inputted value of CLb, in the first equation and then use that value to solve for the wetted length/wetted beam ration "L" in the second equation.
But, once again thanks for the reply.

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### DimSenior Member

on first to yours post, I have understood (not correctly has understood), that the help on job with Excel is simply necessary.

Dim.

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### BrettMSenior Member

Use solver... May be easier to rewrite the eqn to equal zero so you don't have to think next time.... Can also set up a macro button to automate it. Good Luck.

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### nevdJunior Member

Hello,

As a new member, I think your project will be very useful to myself and many other members.

Please advise how the programme is progressing.

nevd

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### nicoSenior Member

Hi,

When u think that all the formular are right,etc.. If i have the file, i could program a bit and add some macros using the solver from excel (I am already using it for a VPP). I think it is easy to understand VB language so it ll be easy to change.

Nico

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### guest12020101217Junior Member

Thank you for the offer. It been on the back bench as l am still waiting for copies of the papers by savitsky from SNAME. Want included pre planing prediction. I will be making the program free on the WEB but not until l am 100% happy with it. Plan to learn VB myself as there is other plans for programs l want to follow up.

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### tspeerSenior Member

Did you ever get a real answer to your Excel question?

There are a couple of ways to solve the equation. One is go to the Tools menu and using Goal Seek. Tell it to set Clb to the value you want by varying Clo.

If you have several sets of equations to solve for, you can have a column of desired values for Clb, a column of Clo values (loaded with initial guesses), a column of Clb's calculated from the formulae, and a column of squared errors. Sum the squared errors in one cell, and use Tools/Solver to minimize the sum of the squared errors using the Clo cells as the parameters to vary.

You can also do it by intentionally setting up an implicit loop and going to manual calculation. Hit F9 repeatedly to iterate to the solution once you have your starting guesses entered.

10. ### GuestGuest

On the web

Congratulations for taking the time to do learn Savitsky by doing this instead of just using available programs.

However, if you want to have a benchmark to check your answers, search on "fishmeal" and "kamen". His site has a free Savitsky program for download.

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### guest12020101217Junior Member

To Guest

Thank you for your support and links. They where very useful

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13. ### GuestGuest

I have already written an Excel spreadsheet to solve Savitsky's planing hulls. Give me your e-mail and I will send it to you. You can either use it, or see how I get Excel to solve Clo by itself.

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### gonzoSenior Member

Would you post it?

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### DingoJunior Member

Here is my spreadsheet on Savitsky and other methods. It contains various allowances for trim-tabs and shafts etc. Unfortunately, it was written by me in Dutch and Afrikaans, but the symbols and references should pose no problem. Any translation problems just e-mail me at: dingo at postmark dot net.

#### Attached Files:

• ###### prestasie.xls
File size:
261.5 KB
Views:
4,955
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