Help SAVITSKY power prediction

[chocomono]

Hello

I have to do a power prediction for a patrol of 20m in length using Savitsky´s method. The length is the only data i have, and I don´t know what parameters I have to suppose and how to get the power by this method. Can u help me, please?

Thanks

[Willallison]

I don't think that you could reliably do a power prediction with so little information - whether by Savitsky or any other reasonable method.
There are a number of variables that you could assume - like CG position for instance, but others, like displacement can vary so much that your predicition could by out by multiples of the correct number

Take a look at this thread. Amongst other things, there is a link to a spreadsheet (by Dingo) with savitsk's

Savitsky Power Prediction

[chocomono]

Thank u very much Willallison

I saw Dingo´s sheet, but I don´t have enough information to use it, and I think I can´t use any software. I have to explain the method and suppose as many things as necessary to get the power.

Thank you again

[RANCHI OTTO]

Give me displacement, hull shape (round or chine), propulsion system and power or speed.....

[Willallison]

Ah - ok - this is a 'school' question - thats different. You must go look at as many similar boats as possible and note down as much info about them as possible - displacement, deadrise, CG etc etc. Many things you wont be able to get info on - like CG for instance, so you will have to make an educated guess about its position

[chocomono]

Yes, it´s a school work. I don´t know anything about high speed vessels, and the only data I have is the length. I have to talk about forms, resistance, porposing, speed coefficient, give a table of planing vessels against Froude number and do a prediction of power by savitsky (I have to give a number).

I made the following data base and I have found some information about the other things (not many), but I don´t know how to do the savitsky prediction of power.

Thank you very much

[chocomono]

Hello

I have read that the best option for this kind of patrol is:

chine forms
waterjets propulsion

and I can suppose:

displacement about 20 T
max speed about 55-60 knots
service speed 15-25 knots

How can I do the power prediction?
Can u tell me something about the speed coefficient?

Thank you

[RANCHI OTTO]

20 t seams to be to optimistic for such top speed and waterjet propulsion plant...

Anyway according to my KR system you will need 3100 hp abt. in order to reach 57.5 knots, but as sed in my opinion the displacement would be btw. 25/30t.

KR = (BHP)^0.551 / (Displ.)^0.476

[chocomono]

Thank you very much Otto,

I will consider your prediction but I have to do it by Savitsky´s method.

Thank you anyway. I will keep in mind your power prediction and weight

[RANCHI OTTO]

Savitsky ,according to my own experience based on model test results, is too optimistic...

The input for a such patrol boat would be:

Length at waterline = 17.00 m > 55.77 '
Beam = 5.2 m > 17.1'
Deadrise angle = 18.5 deg.
L.c.g. = 6.3 m > 20.7 '
Displacement = 27.5 t > 60'627 lbs

try to calculate the bare hull resistance with Sav. with these data...

[chocomono]

I would like to try with Savitsky, but I have a little problem. I don´t know what Savisky said!

[Willallison]

I think what Chocomono is looking for is a copy of savitsky's method.
I'd post one but I don't have it handy - or in electronic format either...

[chocomono]

You´re right.

I want to know how is the method or what Savitsky said. What I have to suppose and how can I get the power prediction.

Thanks

[wdnboatbuilder]

http://www.sname.org/newsletter/Savitskyreport.pdf#search='Daniel%20Savitsky'
Try this link or what was suppose to be a link, anyway good luck.

[chocomono]

Thank you very much!

Savitsky´s method is not explained in this article but it´s interesting and I think it will be very helpful for my homework. Thank you again

Anyone can attach the method?