Design parameters methodology

[hbr]

Have found following formula applied to calculate the area of the hull at a specific station.

AREA at station x =
(SIN((x*Pi/LWL))^2*(cA1_*x+cA2_*x^2+cA3_*x^3+cA4_*x^4)+cA1_*x^2+cA2_*x^3+cA3_*x^4+cA4_*x^5)

cA1_ =
-8*Volc*(32*LWL^3*Pi^8-180*LWL^3*Pi^8*Cp-465*LWL^2*Pi^8*Cp+210*LCBfpp*Pi^8*Cp*LWL^2+64*LWL^2*Pi^8-210*LWL*Pi^8*Cp+525*LCBfpp*Pi^8*Cp*LWL+28*LWL*Pi^8+210*LCBfpp*Pi^8*Cp-1575*LWL^2*Pi^6*Cp+360*LWL^2*Pi^6+420*LWL*Pi^6+1575*LCBfpp*Pi^6*Cp*LWL-3150*Pi^6*Cp*LWL+3150*LCBfpp*Pi^6*Cp-2520*LWL^2*Pi^4+18900*LWL^2*Pi^4*Cp-3780*LWL*Pi^4-18900*LCBfpp*Pi^4*Cp*LWL+37800*Cp*Pi^4*LWL-37800*LCBfpp*Pi^4*Cp+18900*LWL*Pi^2-226800*LWL)/((4*LWL^3*Pi^8+22*LWL^2*Pi^8+35*LWL*Pi^8+14*Pi^8+210*LWL^2*Pi^6+630*LWL*Pi^6+420*Pi^6-2520*LWL^2*Pi^4-5985*LWL*Pi^4-1890*Pi^4-37800*LWL*Pi^2-75600*Pi^2+226800*LWL+453600)*LWL^3*Cp)

the other parameters Ca2_, CA3_, CA4_ are also based on a similar formula(s).

Who can explain from design point of view the methodology that is applied ?

[Guest625101138]

hbr
If you do not know basic stuff like this then this forum is not the place for you!

Rick W.

[Gilbert]

Does that mean you can't answer his question Rick?

[jehardiman]

Originally Posted by hbr

Who can explain from design point of view the methodology that is applied ?

It is a curve fit of some data. In order to know if it is useful, you have to know what the parent model was designed for or how the data was collected and parsed.

On it's own it is just button sorting by who ever authored it.

[Guest625101138]

Originally Posted by Gilbert

Does that mean you can't answer his question Rick?

Yes - my eyes glaze over when I see something like that. I could not resist taking a shot at it.

Rick W.

[hbr]

Yes, starting form the LWL, the boat characteristics are derived.
and as a result the area od the stations are calculated.
From drawing point of view the result is excellent.
Can not find in the theory books (e.g. Larsson & Elliasson,..) any reference and yes the basic math books are providing the nescessary formula for curves (ellips, circle, paraboloc,..) still i didn t found an example expressed with such a terms.
Seems difficult to get some feedback and yes the answer that it corresponds with a curve is right. Could anyone be more specific ?

[hbr]

A nice feedback is that the formula belongs to the applicable model,
what models are there available in order to formulate the hull characteristics in a mathematical way ?
again the theory books about sailing hull design are not that specific.
looking forward to understand this model approach a little bit better.
Do not hesitate to provide me any guidance bacause up to know i could not find any model information so far (nor book/internet)

[hbr]

Originally Posted by Rick Willoughby

hbr
If you do not know basic stuff like this then this forum is not the place for you!

Rick W.

My experience is that there do not exist places for this or places for that and that anyone can learn from any question formulated. if it is such a basic question then it is for a simple man a rather easy action to improve the world and guide to basic info.

[Munter]

Originally Posted by hbr

My experience is that there do not exist places for this or places for that and that anyone can learn from any question formulated. if it is such a basic question then it is for a simple man a rather easy action to improve the world and guide to basic info.

Yo hbr - you may not have picked up on the sarcasm/humour in the first response to your question. It was probably a language/cultural barrier thing. I don't think the first response genuinely meant you any disrespect.

FWIF - I have no idea what your formula is about but I don't feel too stupid to read these forums...

[Guest625101138]

Originally Posted by hbr

My experience is that there do not exist places for this or places for that and that anyone can learn from any question formulated. if it is such a basic question then it is for a simple man a rather easy action to improve the world and guide to basic info.

hbr
My earlier comment was intended as a joke. It is a very complex formula when you consider you have only given us 1/4 of the parameters.

I have made similar formula in Excel spreadsheet that will generate hull sections based on given hull shape constraints and total displacement. I would not dare publish them because they are just too complex for others to fathom.

Anyway I gave up on this type of approach once I discovered Michlet/Godzilla.

Godzilla is an extremely useful fuction within Michlet developed by Leo Lazauskus. It will iterate hull shape at a rate of about 1000 trials a second to arrive at the lowest drag hull. In a around 30 seconds with a computer you can do the equivalent of milennia of trial and error on hull development.

I am sure Godzilla will give a better result than trying to fathom monstrous parametric equations. Life does not have to be that difficult.

Rick W.

[jehardiman]

Originally Posted by hbr

A nice feedback is that the formula belongs to the applicable model,
what models are there available in order to formulate the hull characteristics in a mathematical way ?
again the theory books about sailing hull design are not that specific.
looking forward to understand this model approach a little bit better.
Do not hesitate to provide me any guidance bacause up to know i could not find any model information so far (nor book/internet)

Hbr.

Let us take 100 different "good" hulls that I have speed and powering data on. I can then non-dimensionalize those hulls and their powering on dimensional data (i.e. LWL,LWL^2,LWL^3,V,B,B^2,T, T^2, S, SA, seconds since the beginning of time, etc.) and other non-dimensional coefficients like Cwp, Cb, LCB/LWL, Rn, Fn, moon-phase, etc. I can then, using statistical methods and stochastic methods, come up with a "best" fit set of interlationship curves based on random non-dimesionalized pairings for that data.

There is no real "scientific" basis for the equation and the factors...it is someones informed and overprocessed guess at a curve fit of the data. There has been a lot of this type of pseudo-science since the advent of computers that makes it easy to do.

Get a good book on dimensional analysis, curve fitting, and nomograph development and design (a dying art IMHO). If you are an engineering student, this should have been covered in your very first engineering class.

[PI Design]

Where did you find that formula hbr? It seems to be a way of producing a desired 'curve of areas' based on a pre-selected LWL, Cp and LCB. But it is ridiculously complicated and without more information there is no way of knowing what type of vessel it is supposed to be applied to, nor whether the resulting curve is actually optimal.

I have used a formula for curve of areas that I first saw used by Tom Speer on his Basilicus project - I think he got it from a Russian paper. I developed this for use in ship (not boat) design to allow automated hull generation including parallel mid body and transom submergence. It runs in Excel and the resulting hull offsets can be imported to Rhino for further modelling. I will try and post a copy of it on this site when I get time, but it is quite buggy and needs Solver to be installed in Excel. It currently only works for ships (which have no rocker, just a keel cut up) but I started to develop a yacht/dinghy version which allows a rocker profile to be included and more elliptical cross sections (actually cateneries). It isn't finished and I don't have time to work on it at the moment, but hope to complete it one day.

Cheers,

PI

P.S. I started writing this before Jehariman's post appeared. He is quite right, there is no scientific basis for the formula you give. The remarks about over processed pseudo science are spot on.
Knowing a desired Cp, LCB position etc however is not pseudo science but good traditional nav arch, albeit things should never be set in stone.

[jehardiman]

Originally Posted by PI Design

Knowing a desired Cp, LCB position etc however is not pseudo science but good traditional nav arch, albeit things should never be set in stone.

That is absolutely correct, and something I forgot to point out. Given enough relevent data, you can make things like cluster plots and Poincare charts and use those to make broad connections like LCB should be between 0.54 and 0.56 aft for Fn between 1.3 and 1.4 for a given type of hull form.

[hbr]

Originally Posted by Munter

Yo hbr - you may not have picked up on the sarcasm/humour in the first response to your question. It was probably a language/cultural barrier thing. I don't think the first response genuinely meant you any disrespect.

FWIF - I have no idea what your formula is about but I don't feel too stupid to read these forums...

Yes of course i immediatly understood and i have replied in the same way

[hbr]

Originally Posted by Rick Willoughby

hbr
My earlier comment was intended as a joke. It is a very complex formula when you consider you have only given us 1/4 of the parameters.

I have made similar formula in Excel spreadsheet that will generate hull sections based on given hull shape constraints and total displacement. I would not dare publish them because they are just too complex for others to fathom.

Anyway I gave up on this type of approach once I discovered Michlet/Godzilla.

Godzilla is an extremely useful fuction within Michlet developed by Leo Lazauskus. It will iterate hull shape at a rate of about 1000 trials a second to arrive at the lowest drag hull. In a around 30 seconds with a computer you can do the equivalent of milennia of trial and error on hull development.

I am sure Godzilla will give a better result than trying to fathom monstrous parametric equations. Life does not have to be that difficult.

Rick W.

Rick, of course i understood (and have the nescessary humour). And formulated the reply in the same way
Serious now i am going to have a look to your tip : Godzilla.
Best Regards,
Hugo