boat design - art or science?

If the objective is to deliver one million tons of material to anywhere in the world in 30 days, then carting extra weight around at high speed makes an extremely difficult task almost impossible.

Glad to hear that Michlet was of some practical use.
"...send gold, willingly, as much as you please."
Letter from Kadashman Enlil I, king of Babylon, to Amenhotep III...

 

ALMOST impossible. Remember to keep using that modifier ...or ONR will cut our funding.

"Gladly pay you Tuesday for a [program] today". with apologies to Wimpy

 

The concept that you describe has been found mathematically to offer *huge* potential drag benefits for very high L/B cushions. A certain LCS design was predicated on that feature. However, having personally been involved in divided-cushion tank tests...I can tell you that achieving effective cushion division is 'somewhat problematic', to use one of my favorite mealy phrases designedtoavoidscaringoffgovernmentfundingofcrackpotideas.

Why you ask?

 

If a SES or Hovercraft's air cushion acts as an "air-spring", then having stacked springs of various frequencies is practical. The interactions of these springs to the surface and to each other is not something I'd be taking shots in the dark at. More science, less art.

I know people are working on this topic and have been.

 

How you do dat?

 

You control the pressure by controling the rate of flow either through dampers or baffle valves (activators/louvers). Also I suppose if one could adjust the cross section geometry "at will" this would have an effect (reel in/expand out like a sail?).

I am not working on such a system, nor have I seen these "active" or reactive systems in use or tested. I'd say my guess is as good as yours BMcF, but I know it's not.

 

I don't see how that is the same as having 'stacked' springs, which implies springs in 'series'; compliance thereof and the resonant responses easily calculated (and still dominated by the spring with the lowest 'K').

Cushion damping systems, or ride control systems (RCS), in use today do use active vent arrays commanded by 1s and 0s to add to the damping (modifying the 'b', not the 'K' in the simple resonance model) of the otherwise lightly damped and lively air cushion. The problem with doing that (for 'large' air cushion vehicles) is that the fundamental 'heave bounce' mode (related to compressiblity of the air) is not far removed from Helmholtz (acoustic) resonances in the cushion. The former is essentially spatially uniform throughout the cushion, the latter quite the opposite. Early attempts to control heave bounce (or cobblestone effect) were stymied by the fact that they often amplified - sometimes radically so - the acoustic responses. In the controls world, this called 'spillover'.

A rather savy Swedish SES captain once told me that he believed that "RCS" must be an acronym for "Rediculous Craft Shaker"...but that was before we got called in to replace a well-intentioned but poorly-executed prototype system with one that actually worked well.

Today's active cushion damping systems have reached the point where they are not only killng the fundamental heave bounce..they even kill the first and sometimes second modes of the acoustic activity. But the 'spring constant' remains unchanged....it's all about adding damping.

 

I'm going to work on my hovercraft now, it's just warm enough to scrape off the snow.

I'll be thinking about the "b" or as seen in the drawing below the "C" factor.

http://www.signalysis.com/press/sensors0899_1.shtml

 

I've had a crack at the problem from a non-artistic point of view,
but I was wondering whether the results are realisable.

"Free-surface pressure distributions with minimum wave resistance"
E.O. Tuck and L. Lazauskas, ANZIAM Journal, Vol. 43, 2001.
http://www.cyberiad.net/library/pdf/tl01.pdf

Potters, sculptors, daubers: any opinions?

 

I couldn't understand it..half of it is in Greek.

As I alluded to earlier, your work and Larry's were used (somewhat liberally extrapolated) a few years back to predict that the use of different pressure 'patches' along the length of the cushion in a very high L/B 'fast ocean transport' SES concept could produce huge reductions in resistance relative to a 'single cushion' under the same concept. The 'how to do dat' part is still untouched. I'm working now with an SES design of 11:1 L/B (!) ...same issues are extant.

 

I'm old..it was always 'b' when I was a young lad attentively copying from the professor's chalk board. Somebody must have decided along the way that the damping term was due to be incremented one letter.

http://www.calpoly.edu/~fowen/me422/eqmotmbk.html

 

Thanks BMcF.

A L/B=11.0 SES is certainly an unusual beast.

Just for fun, here's a plot of my calculations of the (Newman-Poole) wave resistance coefficient, C_NP, as a function of Froude number, F, for a "pure" hovercraft with the same L/B.

C_NP = rho*g*R/(B*p^2)
where
rho = water density
g = gravity
R = wave resistance
B = beam
p = mean cushion pressure.

Note that I've set the origin of the graph at C_NP=0.95
to emphasise the humps and hollows in the curve.

Regards,
Leo.

 

A workable SES system ?

To messers:
RANCI OTTO, BMcf, Kach22i and Leo Lazauskas.

Tending to work from the intuitive and then go to the computer and the math
- I'm a little nervous bantering with you guys.
However, Leo invited any potters or sculpters....to jump in.
So here goes:
Having produced a few vessels that operate effectively in " ground " or
surface effect, I can bring some imperical, experience to the table.
Not just as an aesthetic imbellisher.....

- Although we have noticed, that Ferrari Red paint in our tests:
- makes boats go .07% faster than Olive Drab......

On SES.
We did some work with Ulstein and others, a while ago. And we are aware
of the distance that has been experienced between practice and theory.

Some thoughts:
To maximize load and deck space people often come up with rectanguler
ships. Especialy tempting when twin hulls are used.
Now I know one of you published a paper that states that aerodynamics
has a minor effect with conventional craft at displ. speeds. Or words to
that effect.
However, it was also noted, that as Multi - Hulls have less boat below
the water line proportional to the total surface area - aerodynamic concerns
will become a greater concern.

We agree. So wind tunnel tests were done to test a theory of ours.
Not too Earth Shaking. Basicaly, that square boats will be less
stable than ones with pointy ends, as speeds increase.

Results were better than anticipated. So a working prototype was built.
With field tests supporting the lab work.

The people that worked on this project and myself, found a suprising
lack of rigerous inquiry into aeodynamics, re: ship design.

Another interesting consideration re: SES
Given:
That these ships are in " effect " - more low flying aircraft than
canal barges.....
That a safety factor closer to a plane is required to maintain useful
cruise speeds....
Are all composite hulls going to be the way to go ?

Cheers All !

 

Hey now..I painted my Donzi 'Fountain Red' Imron because Reggie found out the same thing as you with regard to 'speed vs. paint color"

Who is 'we'? ..I was on the original UT904 SES design team..much to my later chagrin, I might add. We (Loheed, Gore and I, working with Phil Curran's gang) did get that design fixed before/when it was later built as the UT928 by Oceanfast in Oz.

Every SES I have designed has included the effects of aero drag in the lift-moment-balance calculations and air tare measurements are always done during tank tests. It is indeed important..just hard to reconcile with the shapes dictated by the need to make it carry lots of cattle.. er..passengers..whatever.

SES are not quite in the realm of 'surface effect' as it is now more commonly known as relates to WIGS or air-entrapment hulls. As long as you supply the air from the forward end of the cushion to avoid 'presssure-gradient-induced tip-over', they otherwise operate at extreme speeds without drama. I could go in to a lot more detail about how high speed affects the distribution of cushion pressure and how aero drag affects running trim...anyone want to be bored to tears about the subtle niceties of SES design?

Unfortunately for me..I am not a member of the famous "100 MPH' SES club..those who got to hit that speed on the ole SES -100B got nice lapel pins to prove it. Fastest I have ever been on an SES is 59.8 knots..but she was 47m long, 260 tons, and rock stable doing it. No drama.

Composites?..they're great. So is aluminum. To be perfectly frank, I think both have their merits and both have their drawbacks..and both have been badly used to equal degree in high-speed ship construction.

The UT904 sure was a pretty thing though..all sandwich composite contruction too, as were all the Aa boats ever built.

 

Looks like I'm busted - working with clay.

My hovercraft study model, foam, clay, plastic sheet, and followed by many paper skirts fitted with pins like a taylor.

http://www.hoverclubofamerica.org/forum/index.php?showtopic=412&st=135


http://forums.pelicanparts.com/show...&perpage=20&highlight=hovercraft&pagenumber=2




http://www.hoverclubofamerica.org/forum/index.php?showtopic=962


I'm still fitting the skirt using an artist method of what feels right. I make many mistakes this way, each mistake I learn something new. It's the process not the end results I enjoy.

The next skirt will be drawn using 3D computer software (for a cutting pattern), I imagine in a slightly different direction what the other two skirts before it were, yet building on my experiences and drawing upon them.

In the end it will have to be science, the begining must be artistic, at least for me it's more fun this way.