Definition of Planing

In the new issue (#140) of Professional BoatBuilder Magazine, page 41, there's a graph attributed to J. Hadler et. al. from "Series 62/65; NSRDC Report 4307, Apr 1974" that compares resistance for boats of various slenderness ratios, defined as L(p) / Displ(volume)^(1/3), at various volumetric Froude numbers. If one looks at slenderness ratios of 6.0 and 7.0 there's a clear crossover at Fn(v) = 3.25. As slenderness ratio increases toward 10.0 the crossover with slenderness = 6.0 migrates toward Fn(v) = 3.5.

 

Unstable in what sense?
When I get time I will release here a version of P2D that allows shapes other
than simple flat planes. There is no instability in the ship-wise direction, but
I appreciate that there could be "sideways instabilities" in 3D.

 

Because, as already noted, in craft like light catamarans the water can be leaving the transom cleanly, but the boat is clearly not planing. I would also point out that in some longboard windsurfers the water leaves the transom clearly at quite low speeds, well below planing speed. So you can have a clean wake and still not be planing. A definition that doesn't fit the facts is not much use.

Oh, and try to define "cleanly"....in fact try to define "transom". Where is the clean transom flow on this slender double-ended windsurfer which (from personal experience) clearly planes?
http://2007.star-board.com/images/2007/products/pict_serenity-2.jpg

 

How about this:

-Transition to planing, partial planing, or full planing occurs when:

1: A boat displaces less water than its displacement at stand-still (It rises from water line)

and/or

2: Total hull water resistance reduces despite an increase in boat speed (at a treshold of variable width)

 

So even a slight decrease in displacement relative to static would qualify as planing? It seems to me some boats would meet that criterion even at nose-in-the-air semi-displacement "hump" speeds.

How would you measure that in practice? I think that was the point of the CG proposal in post #2 from Don MacPherson - that wherever the boat's CG is, that's where you'd measure change in freeboard in running-trim photographs. Do I have that right?

Something similar to your proposal might work if you looked at frontal area below the water's surface plane, which at a high angle of trim would occur at the transom, instead of displacement. But again, how would you measure that in practice?

 

Wow, nobody here is even remotely close.

On a more serious note, over the years I've contributed development work to POWERSEA, a time domain planing hull simulator, and even I don't have anything particularly novel to say. Generally we rely on the savistsky reynold's number based pre-planing/planing transition, usually in conjunction with a wink, nod, or 'quote un quote' gesture.

In my view the definition is based on the type of math that can be used to model the water flow. At displacement hull speeds you can obtain generally good results using Havelock sources and sinks. When you get to high speeds the hull sections are impacting, rather than merely perturbing, the water, and the linear potential flow approach becomes less and less valid.

The POWERSEA Kernel uses a highly modified impacting wedge theory by E.E. Zarnick (1978).

http://www.dtic.mil/dtic/tr/fulltext/u2/a052039.pdf

 

Measuring water resistance v.s. speed could be done via fuel consumtion v.s. speed I suppose. Make a graph of gradual increase in speed & fuel consumption and I'm pretty sure you'll easily "see" when the boat starts planing.

Measuring displacement at speed probably more tricky. But probably doable with a scale model in some sort of pool made for similar tests, hull efficiency etc. Pull the model with a string at higher and higher speeds and watch when the water level in the pool drop as the boat starts skimming on the surface?

 

well??

Has anyone solved the mystery of the definition of planing ??
Is it really that difficult to just look at the boat and say it planing !!! yeah!! or no its not planing ooooh !!!
or are they still lost in all that big pile of brown and no one can agree with the other and at the end of the day . come on people whats your problem ?? you all lost in a pile of endless theory and mumbo jumbo and books and figures from 100 years ago !! Maybe its time to simply just push down the throttle lever and let nature do its thing !!

How do you make up you mind what to eat for breakfast ?? is life really that difficult ?? why cant you all at least agree on something !! This tread has run its course and everyone has had they say and has petered out , so what is the simple answer ?? anyone !!!Now remember keep it simple i been told many times here that im not to bright ok !!

 

There lots of things in life that are imposable or nearly so to construct mathematically.

Some examples might be; constructing a triangle from its angle bisectors is in general impossible, deriving Euclid's fifth postulate from the other four, doubling a cube, finding the center of a given circle with the straightedge alone, solving the general quintic equation in radicals. The list can be extensive if you want to look at these sorts of things.

I'm not sure if the actual definition of planing is necessary, in the construct of any specific design, though certainly from a psychological view, entertaining.

 

At the end of the day its just figures on paper and totally meaningless the world has been here for millions of years and will be a few million more who cares !!!

 

The reason you are able to say that is because many people have been writing "figures on paper" for centuries.

 

Which is also the reason he can write it on a KEYPAD of his PERSONAL COMPUTER and send it via INTERNET. And have a CAR which he can drive down to the marina where his GRP boat is moored, turn on the boat's ENGINE and get to his favorite fishing spot. There he can get some beer from the REFRIGERATOR, perhaps turn on the RADIO and listen some nice soft music while enjoying the fishing. Of course, all these things need to have a relative AC/DC ELECTRIC POWER supply and CONTROL SYSTEMS, or they won't work. If they are not made with proper MATERIALS and dimensioned for proper MECHANICAL STRENGTH criteria, they will again not work or will break.
And this list can go on and on and on. All things which have not been here for millions of years but now are, thanks to persons who have done their work with the help of books, numbers and graphs. But, hey, why bother with these details? Let's just spit on other people's efforts, it's much more funny that way!

 

It's this mentality I get so wired on. I'd like to think it's blissful ignorance, but not the case with Tunnels, unfortunately. 4,000 years ago, the Pythagorean theorem was worked on, of course after basic arithmetic and geometry had been worked out. Had he any intelligence, he'd know that the earliest recorded use of "math" was over 34,000 years ago with the Lebombo bone, though this might be a bit obscure for him to grasp, it isn't to hard to grasp that as early as the Paleolithic period, man was attempting to quantify time. Yea, you know stone age men, using tools and attempting to keep track of time, much like some other similarly minded regulars here, that can't believe in things they can't physically grasp.

 

Yeah.... Let's just spit, think math, machines and have fun. Life itself has nothing to do with our..... life.......??????.


Apparently it's not easy to come up with an perspective of planing which suits us all.
Saying that I'm thinking of Royal Vestas Sailrocket which made me wonder when does a vessel actually stop planing; that is on the speedy side, not the side in which the vessel get sucked in again.
In other words; between which phenomena is planing "caught".


And by the way, not only, my dear Tunnels, if we as humanity don't get our act together and priorities sorted soon, seen in the perspective of the total existance of life on earth that is only a couple of decades, we lose it all.
Human existence that is, and possibly more.

 

to me planning is the moment water starts leaving the back of the hull cleanly and the tumbling water is gradually left behind !! then you are planing so to speak!! how hard it it to determin that point in time?? throttle in one hand and gps in the other !! go a littl efaster and then come back to that point a couple of time and the boat returns to tumbing water starting to come back but not touch the back of the boat "THATS PLANNING"

Its like finding the perfect trim each time i go out im my own boat ,i set the rpm 's at 3000 and then use the power trim button and as the nose comes up little by little and the hull finds its optimum planning attatude where it likes to be ,the boat moves easyer and the sound of the motor changes slightly and picks up a few rpms and i dont even have to look at the trim gauge to find that point . Trim past that point the motor will tell you as its harder to push over the water surface ,come back a fraction and motor sound changes back also my hull starts to porpose if its trimmed to far at that speed increase the rpms and knock the trim back a little and its flattens out again . the loading of the boat with one ,two or four people all change the trim requirements but the method of finding that best trim is always the same !!