Resistance prediction for a large B/T

That is what I meant, Pavel.

It's good you have the software but I understand tht finding the papers can be a problem for you. Then, for example with Holtrop and Mennen, you also need to know that there were mistakes in the original paper and find the errata!

Have fun!
Leo.

 

Leo,
Regarding Holtrop and Mennen method,what mistake you meant? Would you please point out?

 

Pavel, have you checked the Savitsky-Mercier regression method? Included in the data base of its origin is the series 63, which seems to cover your range here. It also includes the ser 62, which admittedly is a monohedron planing hull; but it has been tested down to displacement speeds and it also has hull models with similar proportions. Model no 4668 might give you a starting point for a design spiral, it has B/L ~5.5 . With its submerged transom area of ~75% of midship transverse area, at least it may give you a "roof value" for (Resistance/Displacement)-ratio as a preliminary input.

A quick glance at your figures tells you have a Fn(displ) no of 0.78. A rough estimate of waterplane area ~240 m2 gives a bottom loading (Awp/Disp^0.67)~6.5. For the 4668, we have one test series for 5.5 and one for 7.0 recalculated for 50 tons.

The corresponding R/D values are ~0.025 and 0.022 respectively.

 

Thanks a lot baeckmo, I havent yet checked this method but now I will try to study on this. If I have any quarry I will be back to you.

 

Pavel I have another idea for you. Instead of programming an empirical algorithm in your software, you can try to implement a CFD algorithm. If you have difficulties in programming Navier–Stokes equations, you can try with Mitchel equation ( for laminar flow I think ). It’s much faster than “real CFD”, If you want to do so, contact with HSVA, they have already developed such software nu-shallo, and it works just great, so they have experience with this.

 

Michell's thin-ship theory is not applicable if L/B is too low, or if the longitudinal hull slope is large.

 

Another resource on this topic is the recent thesis of Simon Robards which describes a 23
(or more) parameter empirical formula.
It might also apply to your (non-immersed) transom vessel.

http://unsworks.unsw.edu.au/vital/access/manager/Repository/unsworks:3426

The hydrodynamics of high-speed transom-stern vessels
Author: Robards, Simon William
Abstract
In the design of all marine craft the prediction of a vessel's resistance characteristics is a major consideration. The
accurate prediction of resistance is particularly important in the design of modern high-speed vessels where the primary
contractual obligation placed upon the builder is the vessel's achievable speed. Investigation was made of the methods
of Doctors and Day, whereby the traditional Michell wave-resistance theory, published in 1898, is improved on through
a better understanding of the hydrodynamics of transom sterns and the application of statistically determined form
factors.
One of the difficulties with the Michell theory is how to account for the hollow that forms behind a transom stern,
a feature prevalent in high-speed vessels. A common approach in the numerical prediction of wave resistance for
transom-stern vessels is to discretize the hollow as a geometrically-smooth addition to the vessel. Therefore, of great
importance in accurate prediction of wave resistance is the hydrodynamics of, and in particular, the length and depth
of the hollow formed behind the transom stern. Accordingly, a systematic series of transom-stern models were tank
tested at various drafts and speeds in order to determine experimentally the length and depth of the hollow as a
function of vessel speed, draft and beam.
From the experimental data, algorithms for the determination of the length and depth of the transom hollow, have been
developed and utilised in the discretization of the transom hollow for prediction of resistance using the Michell wave-
resistance theory. Application of the developed hollow algorithms produced significant improvements in correlation of
the experimental and theoretical predictions of total resistance, particularly in the lower Froude range.
In addition to the transom-hollow investigation, form factors were obtained using least-squares regression of existing
experimental data. The form factors were based on the major geometric parameters of the models used. In the research
presented here, the method was applied to a large range of published resistance data for high-speed displacement
vessels. Considerable improvement in correlation, between theoretical and experimental predictions of total resistance,
was obtained by incorporating the calculated form-factors into the total resistance formulation.

HTH
Leo.

 

Some brackets are missing in the equation as published in some books and journals

That raises some interesting questions about the peer-review process for these empirical equations. How do we know that there are no misprints in the equations, or in the values of the coefficients. How could a reviewer know that there is something wrong?

Good luck,
Leo.

 

Thanks a lot..... honorable Leo,
The papers of Simon Robards seems to be great. I will study them now. I hope I will get something.

 

baeckmo,
Would please provide any link for any paper which well describes Savitsky-Mercier regression method? I googled but did not sufficient information about it.

 

Thanks a lot Leo,
The paper seems to be great.

 

Baeckmo,
http://academic.amc.edu.au/~psahoo/Research/Int.Workshop-AMC-2003/PSahoo/Lectures.doc
this link has a doc file in which at page 15 I got some notes on Savitsky-Mercier regression method. But I did not understand something. Would you please make something clear to me? :

I am really confused about what is written : "Formulas were derived for the total resistance-displacement weight ratio RT/Displacement for eleven values of the volumetric Froude number, 1.0, 1.1 to 2.0, for a displacement of 100000 lbs"

The matter of 100000 lb displacement is not clear to me. How can I convert the values for the displacement of my boat?

I think the notes are not much detailed what I am wanting.

 

Pavel,

have a look at page 16 of the *.doc-file you posted. There's a formula to correct the RT/Displ. values from the original formula for a 100000 lbs vessel to any other displacement.

Also find attached a paper by Savitsky & Brown from 1976 in which they explain the aforementioned resistance estimation method in more detail.

 

Thanks olav for the attachment of that paper.

 

Baeckmo,
So I con not use use Savitsky-Mercier regression method bellow Fn(volume)=1 ?