Parabolizing lines of existing hulls

[daiquiri]

Originally Posted by Leo Lazauskas

In any case, I hope you can now appreciate what an exciting place Adelaide is.

Yeah, you guys are having some great times down there.
Think that, from my geographical point of view, that fly is landing perfectly leveled and with her head up. If she decided to do some back-flips for the audience then it's probably just her exhibitionist nature... It is you guys in Australia who walk around turned upside-down. I don't want to think about the mess when you have to pee...

[apex1]

Originally Posted by daiquiri

Yeah, you guys are having some great times down there.
Think that, from my geographical point of view, that fly is landing perfectly leveled and with her head up. It is you guys in Australia who walk around turned upside-down. I don't want to think about the mess when you have to pee...

Haah........ now some things become clear to me.

[marshmat]

I hope you're not getting cooked too badly there, Leo. (I'll gladly trade half of your weather for half of mine- we're down below freezing at night now, so your weather plus mine should give us a nice 22 C....)

Perhaps I'm missing something here, but the paper in question seems to be a lot more limited in its scope than the introduction and conclusion would suggest. That one particular fishing boat hull could have its resistance reduced by 15% in the speed range 0.3<Fr<0.4 says, to me, that this particular fishing boat was not optimized for efficiency alone (at this speed) when originally designed. (What will a wider beam do for motion and seakeeping, for example?) But since so few parameters were held constant, I don't see how the conclusion of parabolic waterlines being better can be extrapolated to parallel-middle-body hull forms in general.

It is, of course, never wise to artificially restrict the design space too early in an optimization problem. However, there may be artificial but essential constraints that help to push the design in a particular direction. The fishing boat hull in question was Canadian-designed, thus quota regulations were likely considered in the selection of its main dimensions. To use another example, a Great Lakes ore freighter (square bottomed, and wall sided for 80% of its length) is a long way from an 'optimal' shape from an efficiency standpoint, but since it must traverse canals with strict draught and beam limits, it is an economically acceptable solution.

[Ad Hoc]

Leo
"..I have their FAST 93 paper on fishing boats. I guess that's the one you mean..."
In my fast 93, their paper is not included, says oral presentation only! I was referring to their paper in Marine Technology.

I agree, it is odd to have a paper in such an obtuse publication.

And, as i noted previously, they are not practising naval architects. As you and Matt both rightly note the obvious:
"..They do make one good point - one should not restrict the design space too much in optimisation problems so that good solutions are not immediately rejected because they violate hard constraints.."
"..It is, of course, never wise to artificially restrict the design space too early in an optimization problem..."

One must always do the 'what if' scenarios, as a check, just in case and helps to validate the final solution when questioned by the client!

[Ad Hoc]

Have you ever noticed how you can slowly, very very slowly bring your finger from behind the fly's head and actually touch a fly. If you do this from the front, it flies away immediately. Neat

[apex1]

Try this with the one above John.............

[Leo Lazauskas]

Originally Posted by Ad Hoc

Have you ever noticed how you can slowly, very very slowly bring your finger from behind the fly's head and actually touch a fly. If you do this from the front, it flies away immediately. Neat

I disagree. If you approach slowly from directly in front of them you can flick them right between the eyes. I think they must have a blind spot there. When you get good at it, and I fancy myself a bit at this sport, you can even flick them a little sideways in much the same way as cutting a billiard ball. This sort of thing can really impress girls, BTW.


Leo.

[Ad Hoc]

I've never got them directly from the front....hmmmm....sounds like an "ashes" style challange to me.!!

[wardd]

i have no desire to catch and eat flys

[marshmat]

Being married to a biologist, I have learned that our current crop of apparently identical fruitflies are in fact at least two different species, with different habits and behaviours.... I'm half expecting the genetic tracking experiments to begin any day now.

[apex1]

Now it gets really scientific here.
I like you peers... ..........

Dunno how she thinks about it, though.

[yipster]

gettin confused, o yes me to have some old schoolbooks on fruit fly's

Originally Posted by Leo Lazauskas

If it is about slamming, then it is Korobkin.
If it is about ships in waves, it is Korvin-Kroukovsky.
If it is related to ship wave resistance, it is Kostyukov.

hydrodynamic impacts by A. Korobkin and Korvin-Kroukovsky wave papers that should open somewhere and thanks for your explanation Ad Hoc
amazing how much can be found on the net, here books related to Kostyukov resistance
doing some drawings but should an will get godzilla on screen, dont have a batch switching file huh? (or a free visual basic version )

[yipster]

with nice big glossy buttons? have to see to what can be optimised and almost forgot godzilla is the optimiser
(i only used once or twice) and dont need new optimised hulls to import to check


looked at several waterjets at the marine equipment trade show yesterday
one reply was the boat would start to pulsate as well when the jet somehow would pulse
and reading a bit Korobkinon hydrodynamic impacts i dont find if the idea has any merrit at all
underway you may argue the jet hits new surface anyway etc still i'll ask you experts

[baeckmo]

Sorry,Yipster, I don't follow you. Exactly what are you asking??? Is it about jet performance in a "foaming/aerating" environment, or what? And what is the connection to parabolic lines?

[yipster]

baeckmo, no excuses, i know i'm a wild imaginer and there's no connection to parabolic lines but to mentioned Korobkin hydrolic impact(s) and waterjet drives
way above my head i know but imagine having a shower head taped and facing down on a scale, mine sprinkles, fine or rough, 2 aerating positions but no pulse
would the scale give various readings ? btw, not so shure i agree with propwash in your post 21, props or jets can be trimmed to step out smoothly
or to put the wet delta in a deep hole making big waves due to transit of deadrise to blunt bow trying to break froude nr is my belive