# Savitsky Power Prediction

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

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### Tapsa84Junior Member

If you want to run older software with your brand spanking new win10 super computer, you can just install WMware player, download the older windows image for free and install it on a virtual computer. Easy and works wonders!

I have had to do this on occasion in software development.

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### arkieNew Member

Hope it's not too late to thank you for the answer. Yes, these results were obtained with epsilon consideration. The problem was that my scope included outboard motors and stern drives. Besides the propeller, they have a lower unit which creates a lift affecting significantly the balance and trim. I have added to the Savitsky's algorithm lower unit forces calculation and the results were very close to reality. The model accurately predicts trim change as the reaction to prop-keel angle variation, which is in a good accordance with experimental data. This new algorithm is implemented in my simulator, which is free and can be downloaded from Test Range http://www.sounddesign.sp.ru/marine/range/index_en.htm

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Hi Dingo and folks,

Firstly, thank you to Dingo for sharing your amazing work.
I have tried to calculate the speed a planing craft by using your tool but I think it didn't work well since '#VALUE' appeared on the row of 7 - 55 kn. Hence the graphics starts from above 55 kn (please find the attached file). The excel worked fine with your default parameters.
Did I miss something important? I am curious to find out my mistake.
The parameters of my planing craft are:
Lwl: 10.33 feet / 3.149 m
Beam: 4.79 feet / 1.46 m
VCG: 2.40 feet / 0.73 m
Displ: 2,315 lbf / 1050 kg
Angle of thrust line: 0 degree (since I would like to use outboard engine that the shaft is 5 cm below the keel)
f: 2.59 feet / 0.79 m

LOA: 13.78 feet / 4.2 m
Bmax: 6.23 feet / 1.9 m
Z: 2.46 feet / 0.75 m
Hss & Bss are 0 since I don't have superstructure.

N:1
I wouldn't utilise trim tab. But I read previous post that using outboard engine should set shaft and strut to zero while setting small number for rudder. Hence the rudder parameters are:
c: 1.84 feet / 0.56 m
t: 0.59 feet / 0.181 m
A rudder: 3.21 feet^2 / 0.298 m^2
Xc: -0.05 feet / -0.014 m
Yc: -0.87 feet / -0.266 m
Thank you

Kind regards,

#### Attached Files:

• ###### Planing craft calc of 4.2 m.jpg
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### Mr EfficiencySenior Member

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The displacement is not 2.315 lbf , it should be 2,315 lbf or 1050 kg. Thank you for pointing out, I'll correct it soon

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### Mr EfficiencySenior Member

Sounds way high to me, 2315 lbs.

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### Olavnaval architect

I second Mr Efficiency's opinion, the displacement seems rather high for a planing craft of this size.

But something else comes to my mind: Where is your lcg? I cannot find anything about this in your particulars. Did you leave it at a default value that is much larger than the overall length of your boat (I have a copy of Dingo's spreadsheet that I believe still contains the "original" data, with lcg = 29 ft)? If yes, this would explain why the calculation did not work.

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Okay I missed that point, thank you for noticing it
the LCG has been set at 4.265 feet / 1.3 meters
However, I still haven't clue about the '#VALUE' for 7,8 and knots of speed. So the graph is still untypical, I believe. (please check the attachments)

#### Attached Files:

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• ###### Planing craft calc of 4.2 m-new.jpg
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### Olavnaval architect

Remember that the Savitsky method is all about finding an equilibrium for all forces and moments. With a boat with such a high bottom loading I reckon there is no solution for the slow speeds, as the required trim angle for the necessary lift would be too large (i.e. > 15 deg as indicated in the spreadsheet).

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### vkstratisNaval Architect

For anyone interest, you can check our quickPlaning for Windows software. quickPlaning is a simple windows desktop application that offers resistance prediction for planing crafts using the Savitsky's method as well as preliminary propulsion analysis using the GAWN propeller series. You can download and evaluate quickPlaning at www.boatdesignlab.com.

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### Manolo RdENew Member

Problems arising with the last versions of Excel which has built-in functions named "Function" and "Lamda" (see attached captures image). Any ideas...?

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• ###### problem.jpg
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