Definition of Planing

You have already asked that question few pages back, but oddly I was the only one to reply.

Citing my previous post:

I would say that it (percentage of hydrodynamic lift contribution) 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.​

 

Two different but related topics:

What is planing?

How can a determination be made if that a boat is planing?

 

I don't think anyone disagrees with that definition of planing, but it is very hard to see, feel or measure in the real world. Also it may be necessary to add that only hydrodynamic lift from water-air boundary is accepted, not submerged foils, thrust etc.

And even to that definition there may be some exception like racing boats with aerodynamic lift carrying most of the weight. I guess these would be considered to be planing as long as they touch the water.

To also allow those special cases maybe: "Hydrodymanic lift from water-air boundary is at least equal to the dynamic displacement", which would be equal to 50% of weight for most boats.

 

Leo,

I'll admit, I don't have the patience, time or inclination to follow this thread too closely but I am curious: Are you any closer to a refined definition of planing?

If so, what is it and if not, why?

Thanks,

 

No there dosent seem to be any one getting close to a answer because there is no simple answer it seems !! theres to many variables and just as it get close then something else gets tossed into the boiling pot .
Why is it so difficult to simply say yes its planning once it reachs this point where the water is leaving the transom cleanly and tumbling water has left there !!

 

It is difficult because it just ain't so. I have been on a simple 18' boat that is making 20mph and the transom has long since cleared of tumbling water but it still had a lot of high trim and was making a huge amount of wake. Doesn't fit any definition of planing I can think of. Top speed with a 115hp outboard was 28mph. Bad design and overweight to be sure but the world is full of boats like that.

There is simply no suitable technical point that is always applicable to define when a boat starts to plane. We can always tell if a boat is in displacement mode or when it is fully on plane but, in between, different boats have different habits. All this conjecture is like counting angels on a pin head.

 

Posts are getting easily lost in this quickly-growing thread. Please let me reiterate what I wrote in the post #190 , so that we can discuss it, if you wish. Here it is:

We have never considered the waterplane area in the previous discussion, or perhaps I've missed it. However, in the general hydrodynamic lift equation: L = 0.5 rho V^2 S Cl two things can change with speed - the lift coefficient "Cl" (depends on the trim angle) and the reference area (which can be either the waterplane area, or the wetted surface) "S".
futhermore, also in view of Leo's theoretical work on 2D planing plates and Ad Hoc's post #64, there's the known fact that the wave drag becomes progressively less predominant with speed when the boat is on plane.

So, perhaps hydroplanes, stepped hulls etc. could be included in the general definition of planing by stating that a boat of a fixed weight and fixed configuration of the propulsive device is in the planing regime if the following 3 conditions (and their combinations) are satisfied:

1) the wave drag decreases with increasing speed
2) the trim angle decreases with increasing sped, for constant waterplane area
3) the waterplane area or the wetted surface decreases with increasing speed, for constant trim angle.​

Are they sufficiently comprehensive, measurable and consistent with the practical observations, or do you folks have counter-examples which could prove they're still insufficient?

 

In reality it is planning !!
its really only you opinion that its not ??
sure its out of ballance and dosent tick all the boxes in YOUR check list but Its planning !!
its all these personall things people keep adding is why there is no deffinate answer !
When a boat is doing this ,it means its planning . full stop no more end of story !!
no more buts and because of this means dadadadadada!!!

 

Well, and what makes you believe that your personal opinion (by the way - wrong) is the ultimate and undisputable answer to the question?
I can give you an example of a boat which can have a water flow leaving the transom cleanly even at displacement speeds. Just cut the transom so that it's lowest point is just above the water surface. Even at very low speeds you'll get to a point where the water will leave the transom very smoothly. Is it planing?

 

What is the intended use of the desired definition?

 

How is that relevant for the discussion?

 

Yes in my book yes it is !! now forget all the technical stuff you all hung up on and get back to absolute nitty gritty basics , it is running at an efficent speed and shedding water and pushiing it aside and planing !!. cutting through because of its shape !!! its never going to plan (in your sense of the word )even it it would do a 100 mph .no two boats will ever plane the same as the next each one has a personality of its own !!it seems everyone is so caught up in facts and figures and computer prodictions you have all lost the pure pleasure of boats and boating . At some point hulls plane !! no one here is able to say where that point is !! everyone has a differant interpritation and keep moving the point to suit there own ends and meaningless predictions so they look good . I found the answer so there !!!

 

Ok, thanks. That was a very poetic and emotional view on boating - and planing.
Unfortunately Leo needs a definition which can be measured and quantified, and not just felt deep in our hearts. So I propose to get back to the opening question of this thread and to concentrate our efforts on trying to carry on the technical aspect of the discussion.
Cheers

 

I mean no disrespect but I suppose the only way to end this is to admit that tunnels "opinion" is superior to all others. The boat I mentioned and that tunnels says is planing, was making 20mph but, it was pushing a huge amount of water (which means that it was laboring and not yet "over the hump") and was a beast to steer. If that is planing, I want no part of it.

I still invite you to look at the series of photos I posted on #163 ( www.bluejacketboats.com )and tell me when the boat goes past the displacement/planing point. Notice that the bow trim never does fall, even at top speed when much of the boat is out of the water. Water flow clears the transom at about 9 1/2mph. The displacement in these photos is about 2400# and the power is a Yammy50.

 

Tom, from the pics in your site it looks evident that the trim is rather constant but the waterplane area gets smaller as she speeds up.
Do you think it conforms to the criteria in my post #202? To me it looks so.