Savitsky Power Prediction

[rahaman]

Dear Mr. Dingo,

Thank you very much for your reply. Your work is really excellent and thank you once again for sharing your knowledge and work with us. I can understand the effort you made for completing your works and I have no intention to do the things you mentioned in your mail because we professionals must have some ethics.I just seek the password only to convert some headings in your calculation that is written not in english. I would like to mentioned here that I have collected all the papers you mentioned in your calculation and I read all of them. So for me now your calculation is understandable and your spreadsheet is running properly.

Thank you very much.


Dear Mr. rxcomposite,

Thank you for your advice but I am not interested to do that.

[Dingo]

Rahaman, what is your e-mail address? I will send you the password.

[Dingo]

Regarding demi-hulls, there is a paper by Mustafa Insel of Turkey that addresses this subject. This is the paper that I was going to use to add to the Planing.xls spreadsheet. My copy is currently in storage since I moved and will take a while to retreive it.

[rahaman]

Dear Mr. Dingo,

My e-mail address is rahaman@triton.naoe.t.u-tokyo.ac.jp

Thank you very much.

Rahaman

[Sercan]

Hi Dingo,

This is an old thread but I still want to reply because I'm confused about the critical trim angle before porpoising. I see the critical angle results from Angeli and from Lewandovski on the excel sheet. And they are different. On the other hand some people uses Savitsky 1964 in order to find the critical angle. Which one is more realistic? And also what to do for warped hulls, because I think all these methods are for prismatic hulls.
If there is anybody out there still interested in the subject Im waiting for some advices.

Thank You very much
Sercan

[Dingo]

Sercan,

Savitsky, from memory, predicted the running trim angle, not the critical trim angle (note, from memory, but please correct me if I am wrong). Angeli and Lewandovski gave different theories on when the porposing angle occurs. My opinion is to use the lesser of these angles to be on the safe side when designing the vessel.
Regarding warped hulls, this spreadsheet takes into account the warped hull. That is why the deadrise at the transom and amidships is required; they do not have to be the same.

Dingo

[Paul Kotzebue]

Hey Dingo,

It's been awhile since the AAA days in Bremerton. Good to know you're still at it.

[Yellowjacket]

While we are on the subject of your most excellent spreadsheet, perhaps you could explain what the limitations are on the maximum valid speed for the analysis.

The maximum speed is calculated as 13 x the square root of (g times the beam) all over 1.688.

I was curious as to what part of the theory this is based on and why it this is so.

Also many thanks for creating this fine piece of work, it obvoiusly took a long time and it has been a huge help in some analysis I was doing.

Thanks,

[Sercan]

Originally Posted by Dingo

Sercan,

Savitsky, from memory, predicted the running trim angle, not the critical trim angle (note, from memory, but please correct me if I am wrong). Angeli and Lewandovski gave different theories on when the porposing angle occurs. My opinion is to use the lesser of these angles to be on the safe side when designing the vessel.
Regarding warped hulls, this spreadsheet takes into account the warped hull. That is why the deadrise at the transom and amidships is required; they do not have to be the same.

Dingo

Thank you very much for your reply
If you check Savitsky 64 , page 92 you will see that there is a graph showing purpoising limits for prismatic planing hulls ( for 0,10 and 20 degrees of deadrise angle). I think you are right , Its a good idea to use the lesser of these angles.

[Victor T]

Originally Posted by Sercan

Thank you very much for your reply
If you check Savitsky 64 , page 92 you will see that there is a graph showing purpoising limits for prismatic planing hulls ( for 0,10 and 20 degrees of deadrise angle). I think you are right , Its a good idea to use the lesser of these angles.

Porpoising regime of planing (by Savitsky 64) is calcs in Free!ship Plus v3.07+.

[Dingo]

Yellowjacket,
From memory, Savitsky tested a few models and obtained parametric formulas for their performance. Any theory is only valid for the particular set of models, speeds etc. that were tested. In this case, I assume that Savitsky concluded that his theory was only valid within given parametric boundaries, hence the speeds were valid from 0.6 x sqrt(gB) up to 13 x sqrt(gB). Beyond these speeds, the theory may or may not be valid.

[Yellowjacket]

Originally Posted by Dingo

Yellowjacket,
From memory, Savitsky tested a few models and obtained parametric formulas for their performance. Any theory is only valid for the particular set of models, speeds etc. that were tested. In this case, I assume that Savitsky concluded that his theory was only valid within given parametric boundaries, hence the speeds were valid from 0.6 x sqrt(gB) up to 13 x sqrt(gB). Beyond these speeds, the theory may or may not be valid.

Dingo,

Thanks,

I was looking at some analysis for high speed small monohulls with zero deadrise, and the analysis showed improvements for narrower planing surfaces. As you go to higher speeds, the trim angles are getting very small, so it is not suprising that a narrower surface will provide lower drag since you can't get the CG far enough aft to make the planing surface efficient.

The problem was that I was quickly getting below the minimum beam and was wondering why the analysis was limited at this higher speed. As we look at very high speed hulls, such as padded v hulls, you can easily exceed the recommended speed limits for Savitski so perhaps I should look at the work that Jim Russel has done in this area as this may be more appropriate.

Not sure myself as to why there should be an upper speed limit for the analysis based on beam. I can see a lower speed limit, since the edge effects become pronounced and you are falling off a plane. But at higher speeds, the trim angles become lower and the effects of edge losses are not as pronounced. What I'm saying is that I can understand an upper limit for the analysis, but I had trouble understanding why it would be based on the width of the planing surface.

[sandmanclose]

Dear Mr. Dingo
may be I late to read this forum, but I really interst with your spreadshet, I really want convert your program in matlab language, can you give me your password sheet protection
please send to sandmanclose@yahoo.com

[Adis]

Dear Mr. Dingo,

I would like to thank you for giving in public such a wonderful spreadsheet. It is an amazing piece of work, and I appreciate your kindness to allow all of us to have such a valuable tool in our hands!!!

Thank you very much again!!!

[XXL]

Dear Dingo,

I programmed Savitsky equations using Basic HP on a workstation, then with HTBASIC on a PC years ago., for my studies.
I would like to program it now under Excel and to have a basis for a transverse step planing hull calc. using modified Savitsky equations.
Would it be possible to have the password of your file in order to have a sound basis for my new program of hulls with steps?
Thanks a lot for your answer and for your help.

kind regards
Michel