Definition of Planing

Gonzo, that's a nonsense. It does travel through water, though for a very short time. It cannot just bounce off as if water instantaneously turned into ice. If you try to slam it perpendicular to the water surface, it will not bounce off. A high forward velocity is required, compatible with one of fundamental requirements for planing. Same for skipping stones.

But... At this point I propose to leave the ball case for much later stages of discussion. We are unable to find an agreement on planing of much better known common hull forms, let alone stuff like spherical balls. Let's first try to do that, then we'll see how it applies to more general geometric forms.

 

Does anyone disagree with that "a vessel's weight is supported more by hydrodynamic forces than by buoyancy" is necessary for a vessel to be planing? Or can a vessel be planing without that statement being valid?

 

Your are neglecting the thrust and resistance/drag and the resulting moment in your trim equilibrium analysis. The magnitude of thrust and resistance vary with speed and the location of the resistance also changes. The effect of the resulting moment and thus its effect on trim will vary with speed.

 

I would say that it is the physical essence of the planing, and hence should be the fulcrum of the discussion and the main parameter of verification of calculations.

But, since several writers have pointed out the difficulty of:
1) establishing the right value of the hydrodynamic/hydrostatic ratio at the inception of planing, and
2) reliably empirically measuring the said ratio,
the discussion has turned towards other ways of identifying the planing condition. Trim, heave, wake, etc.

 

back in post 72 I asked the following question-

This preceding discussion is why I asked that question.

Do we want a physicist's definition that describes planing as a hydrodynamic phenomena applicable to arbitrary solids, or do we want a mariner's definition that considers intelligently designed boats operating as intended?

The first corresponds to my first question earlier. The second one to the second question.

If we are more interested in the second one, the next decision is whether we are solely concerned with hull behavior, or do we want to include appendages, propulsion, and aero forces. As a sailor, it seems a bit silly to ignore aero lift. That is the dominant upward force on the skiff in the previous pictures.

 

Am I the only one here with that uncomfortable feeling of being stuck in the middle of a minefield?

 

And, if 60% of a vessel's weight is supported by hydrodynamic forces, is it
planing more than one that has only 50% hydrodynamic support?

 

Yellowjackets arguments are good enough for me, I now understand planing, always happy to learn something new! Thanks, and thanks also Leo for the great comment about the planing splash, and for starting this thread. Thanks also for the RX-windsurfer paper, in which your friend E.O. Tuck's 2D theory does seem to perfectly confirm Yellowjackets findings.

 

I'm sure Ernie Tuck would have loved to see this discussion, but it is not his
theory. 2D planing theory has been known for a long time, at least since
Sottorf (circa 1929) and Sedov (circa 1932).

IIRC, Squire (circa 1957) was the first to recognise that the lift force must be
an input rather than an output, and Ernie's student Oertel (circa 1975) was the
first to appreciate that, in practice, the moment of the lift force must also be
an input rather than an output of the theory.

 

Unless we start pouring vodka down your throat, you should be ok

from wiki- http://en.wikipedia.org/wiki/Shtrafbat

 

Not really, in the limit, as the increment of speed becomes small, the effects of thrust and resistance become second order and don't really effect the results. If you look at large changes in power, then yes, but but we are focusing on the area where planing begins, and what happens there is that the trim angle is falling with very little increase in thrust.

 

Ok simply now !!
When is bouncing not planing and when is planing not bouncing ??????? so if its bouncing its really planing !!!so the planing is causing the Bouncing!!!!
If its bouncing and planing its traveling across the surface of the water and not travelling through the water !! if it was traveling though the water it would be submerged beneith the suface!!,but its not submerged beneith the surface its planing on the surface of the water !!! if it was submerged it would be impossible to bounce or plane untill it was on the surface !! then it could bounce and momentarily leaving the clinging of the waters surface to launch and fly through the air to be able tofall again and bounce off the water and fly through the air yet again but because itlooses momentum each time due to skin friction and the water clinging to the balls surface for a slightly shorter distance falling yet again and retouch the surface to then in the state of planing and if it hasent slowed sufficently to bounce yet again then it will stop and is neither bouncing or planing but simply floating !! untill its picked up and the ball is hurled with great force and the whole process is repeated all over again !!
Any of the bouncing ,planing, flying, clinging ,floating make sense ????? forgot about skimming across the surface !! skimming must be another word for planing ! ,skimming,skipping , sliding, sliping !!! WHAT EVER !
Time for a coffee atfer all that !! its really makes me tired all this having to use those lonely braincells !

 

I visualize the ball as hitting the water and bouncing, not moving any significant distance through the water.

 

Ok then, back to balls.
It looks like the elasticity indeed does play a role in the planing of balls, together with density. I've just found this video on you tube: http://www.youtube.com/watch?v=k4767cZzS28 which shows some examples. It treats balls of small diameter and relatively high density. A bigger, air-pressurized ball probably has a better chance to bounce off due to lower density, but gets less help from the elastic deformation of it's skin. Perhaps there is an optimum combination of inflation pressure and diameter for a given speed?

Gonzo, you can clearly see that those balls do get quite some way into the water before skipping upwards.

 

There appears to be agreement that "a vessel's weight is supported more by hydrodynamic forces than by buoyancy" is necessary for a vessel to be planing.

A claim has been made that when a vessel is planing the trim angle must to go down if the speed increases.

What is a vessel, perhaps one with other than a prismatic hull, doing if above a certain speed its weight is supported more by hydrodynamic forces than by buoyancy but the trim angle does not go down if the speed increases? What term should be used for that situation?

Perhaps there will be a reply that this question is moot because the situation can never happen. If so then there is no need to use "trim angle must to go down if the speed increases" as a necessary condition to define planing. All that is needed is "a vessel's weight is supported more by hydrodynamic forces than by buoyancy".

But I'm not convinced that there are no vessels, including ones with non-prismatic hulls, which above a certain speed have their weight supported more by hydrodynamic forces than by buoyancy and their trim angle does not go down if the speed increases. So back to the first question - what is the vessel doing if not planing?