Savitsky Power Prediction

[Dingo]

Here is the Planing spreadsheet with the correction for the trim tabs. Sorry for any inconvienence!

Has anyone looked and used the theory in the paper "A Rational Prismatic Hull Approach for Planing Boat Analysis" by Richard A. Royce, Jan 1994, SNAME local section paper of the Great Lakes (also on the Small Craft CD)?

[Dingo]

I was asked by CGN on another thread what the section by Lewandowski is for on the spreadsheet Planing.xls
This paper set out the dynamic stability for a planing vessel. For a given angle of roll, the restoring moment in ft-lbs is calculated (note: a negative moment means a restoring moment, positive is non-restoring).

[CGN]

Thanks dingo, I much appreciated your help

cheers

[Janamon]

Hi Dingo.

I'm working through your excel spread sheet. Have you a copy in English. I just can't work out some of your symbols. If you could help me that would be great.

Cheers John H
ngaire_john@xtra.co.nz

[vankamal07]

i am new here, and a young naval arc, i want to predict my boat using savitsky method because what i know this method suitable for planning hull.

so i had got all the particular from that formula, but i still confuse with one thing, my boat length overall is 12.0 meter, and LWL is about 10.33 and her draught is 0.53 meter.

what the problem i get, when i calculate the Lk from the savitsky method it give larger than my length's boat. why? and it give the effect for power prediction i getting. here i attached for you the results i get. i just attached the Lk result and speed and power prediction i get only.i just want know, it is what i get is correct or false to compare with my length of boat.

please help me senior and junior :rolleyes:

[Dingo]

vankamal07,
Please give me more details on your vessel especially LCG, displacement, speed etc. I can't analyze any results without knowing more about the vessel. One thing I can tell you is if the LCG has been assumed incorrectly, the value of Lk will vary. Note that Savitsky's method does not take into account the length of the vessel since the beam dimension is what gives it its lift. The length only comes into play to calculate wind resistance etc.
Dingo

[vankamal07]

Thank dingo for your co-operation,

Here i state the particulars of my boat and the results i got.

Boat's particulars:

Weight = 4.5 tonnes,
Estimation LCG = 4.72m from transom,
Beam = 2.76m
Deadrise = 15 degree

Results:
Based on Savitsky's method, i got
at 50 knots,
λω = 2.414,
trim = 1.452,
Lk = 11.31 m
Ds = 0.29
Stotal= 19.03
EHP (hp) = 551.7 hp

So , i hope u can tell me what wrong in my calculation.

[Dingo]

Vankanal07, I could not get the results exactly that you had since I still do not know your VCG, angle of shaft etc. What I did notice is that under the comments column, it displayed "Note: Not Planing". This method is used only for planing vessels, so Lk could be wrong for your vessel.

[vankamal07]

dingo i appreciate on your help, i am new in this field, so i don't have enough knowledge an experienced, i hope u can guide me...dingo can u give me the methods of your calculation...so that i can study on and find the answer from it...

[Dingo]

If you look inside the tab entitled "Berekenings", you will see all the calculations. On the very right-hand side of the columns I have listed all the references and papers which I used. Hope this helps.

[rxcomposite]

What is the best method to predict the performance of a demi hull planing catamaran? The flat side of the hull is located inboard. Section shape looks like a tunnel boat.

[rahaman]

Dear Dingo Tweedie,

I have found your latest planing spreadsheet. It is very nice work. Thank you very much for sharing your excellent work . Is it possible for you to provide the password of your spreadsheet? I want to do some calculation by using your spreadsheet for my graduate report and I have to submit my report on next Tuesday(2/9/2008). So, if possible please........

Thank you once again.

Rahaman Md. mashiur

[Dingo]

Dear Rahaman,
The spreadsheet should work without needing a password. All calculations and formulas are visable, and the macros work. If the spreadsheet has a problem running, let me know.

[rxcomposite]

Rahaman,
You may try copying the sheet to another spreadsheet. You will lose some macro but the cells can be edited. Dont edit the formulas however.

Dingo,
I tried this to disable the password because I have an officemate who is Dutch Afrikan. He says the words are in Dutch German. He was able to translate closely most of the word anyway. I find your work very complete and I want to know how everything connects so I need to decipher some words.

Rx

[Dingo]

The reason that I lock the spreadsheet is so that no one can tamper with it and re-post it, or submit it as homework by tweaking it and calling it their own. It took me a long time to write it, but, for the purposes for sharing engineering knowledge, I allow the formulas to be seen, and all the macros to be read. Nothing should be hidden; all references are also able to be read (see the right hand side in Berekenings). I am willing to explain my logic and any translations required if asked. I hope that this seems reasonable.