theoretical displacement hull shape for min drag

[yipster]

before the thread started i was watching rowboat racing and saw how deep the bow burries during strokes
and was impressed from the quik speed reduction between strokes ( on 4 "engine" boats even more )
i wondered if the sinking could have anything to do with slender ships like those fast boats from the thirty's

thanks again for the wardoss hull form witch satify's my curiosity, i'm trying to get a shaded visual out of the .mlt file
to get a better idea of the, i gues dolfin bulbnose, this without succes so far

like to input a dented bottom hull with a volume keel sticking out of the dent checking on area rule but thats a nono eh?

have to learn a bit more NA to quiker compare out files but started using Dr Leo's acronym
planty very intersting hull shapes and must say the program is a gem.

i'm still looking for a virtual tuft becouse gee, how did i make those batch files long ago?
and sorry, no cant help with verification i'm affraid

 

[Leo Lazauskas]

y's

thanks again for the wardoss hull form witch satify's my curiosity, i'm trying to get a shaded visual out of the .mlt file
to get a better idea of the, i gues dolfin bulbnose, this without succes so far

Thanks for the kind comments, Yipster.

Some of these minimum wave resistance hulls have very unusual bows
as shown in (attached) fig29 and fig30. The hull on the left of
fig29 has a fairly normal bow, but side bulbs.

The measured resistance of Ward's Optimum Symmetric Ship
is shown in fig37 from Wehausen's monograph, "The Wave
Resistance of Ships". The drag curve you calculated using
Michlet should be very similar to the one shown in that graph.
The low drag seems to be confirmed by experiments, which is
a pretty good result for Michell's theory. More so because
the bulbs are so large that Michell's fundamental
assumption (small longitudinal hull slope) is violated at
some places on the hull.

Of course the residuary resistance (wave + form drag)
is much higher, as expected.

It is a funny sort of result for mathematical hydrodynamics.
Once again, mathematicians have shown themselves to be clever,
but not very practical! On the other hand, there are some features
of the weird bulbs that are similar to the sonar domes on some
naval vessels.

I think it's one of those research projects that just had to be
done, even though the ultimate outcome was not particulary useful.

Regards,
Leo.

P.S. fig29 and fig 30 come from:
"Optimal ship forms for minimum wave resistance"
Chi-Chao Hsiung,
Report No. NA 72-1
College of Engineering
Uni California, Berkeley.
August 1972.

 

[yipster]

thank you, wobly hull and bulb visualised, i'm on it and comparing but playing chess (level7 on vista) with a frend as well
old drop out that i am i was in berkely at that time but for a rock concert. btw, resistance in kN i asume, wikipedia say's

1 N is the force of Earth's gravity on an object with a mass of about 102 g (1⁄9.8 kg) (such as a small apple).

On Earth's surface, a mass of 1 kg exerts a force of approximately 9.80665 N [down] (or 1 kgf).
The approximation of 1 kg corresponding to 10 N is sometimes used as a rule of thumb in everyday life and in engineering.

The force of Earth's gravity on a human being with a mass of 70 kg is approximately 687 N.

1 kN equals 101.97162 kilograms of load, but multiplying the kN value by 100 is a good rule of thumb.

 

[johnhazel]

.......

I don't think that we ever satisfactorily explained the strange "optimal" pressure distributions shown in:
"Free-surface pressure distributions with minimum wave resistance"
http://www.cyberiad.net/library/pdf/tl01.pdf

.... At high speed there is definitely something like hydrofoils at the ends.

Leo.

I looked at the hydrofoil wakes shown in a NACA report from:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930087415_1993087415.pdf

It seems the min resistance condition for the high speed case might be a result of the trailing pressure bar (or hydrofoil of a dual hydrofoil assisted cat) could be surfing down the face of upward moving wake from the leading pressure bar (hydrofoil).