Resistance prediction for a large B/T

[Leo Lazauskas]

Originally Posted by b1ck0

...
Mitchel equation

For the non-English speakers here...

"Michell" is not pronounced like the French "Michelle". The first syllable rhymes with "rich".

"Froude" rhymes with "dude", not with "crowd".

Don't make these simple mistakes, or people will laugh behind your back at hydrodynamics parties.

Leo.

[baeckmo]

The referrence posted by Olaf is the one I had in mind, and yes, the limit of application is 1<Fnd<2. At Fnd=1, the writers mention an average difference measured/calculated of 6.0 %, and increasing in the low Fnd range.

Extrapolating down to Fnd=0.8 is questionable, of course. If that is your only way, however, then you should plot the coefficients (A1 to A27) versus Fnd. Then apply a curve-fitting function to each and see if they change smoothly in the low Fnd range. If so, they may be extrapolated down to Fnd=0.8. Of course this is increasing the the mean fault range, but if no other way is available, you have to use whatever information you can get, and be aware of the risk level. That is the essence of engineering, irl!

Recalculating for another size is of course conducted "as usual"; separate the friction area and its friction losses from the rest of the losses, recalculate for a new Reynolds no, with a new friction coefficient. The recalculate friction with the new wetted surface and speed and recombine with the residual resistance. In this range though, the real Cf-values are quite flat and the major influence comes from the relative "unsmoothness" of the surface, but that should be simple piece of cake for a NA.

[pavel915]

Originally Posted by baeckmo

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.

Baeckmo,
Model no 4668 is of which series? How can i find information regarding this? I need any model test data which is close to my boat, then I will have a smell that what should be the characteristic of the resistance curve of my boat.

[baeckmo]

"Resistance tests of a systematic series of planing hull forms",

E.P. Clement, D. L. Blount, SNAME 1963.

[pavel915]

Originally Posted by baeckmo

"Resistance tests of a systematic series of planing hull forms",

E.P. Clement, D. L. Blount, SNAME 1963.

Baeckmo,
I googled a lot,,,but did not get that paper.
It is not available free?