Author Topic: Will it Plane?  (Read 15441 times)

PonoBill

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Will it Plane?
« on: June 29, 2016, 08:55:58 AM »
This topic is kind of nonsense, most people won't care, but there's a reason our boards don't plane, and it's a good one. It would be easy to build a planing downwind board. Copy a modern windsurfing tail. For the one percent of the time that the board might plane it would work well, for the other 99 percent of the time it would suck.

Anyone who windsurfs knows what planing is about. Your board pushes and pushes, but if you have enough wind and a good board you can give a little pump, or transfer some added weight to the boom, and the board pops up onto the plane. You immediately accelerate, because planing offers much less friction. The lift component picks most of the hull out of the water and skin friction is confined to a small area. Planing enables planing jibes because a board that is planing generally has speed in excess of that required to come up on a plane. With the lower friction you can coast through the turn, losing speed but remaining on a plane if you started the turn with enough excess speed and you turn quickly and smoothly enough to still be planing at the end of the manuver. You can make the turn with minimal sail power because you're costing down with excess speed.

Now try that on a SUP with a mast track. You get going quite fast, but no matter how hard you pump, you won't get up onto a plane--because the board has no planing surface. the continuous rocker in the tail won't pop up onto a plane except in very rare circumstances. If you try a planing jibe your board slows dramatically, because you aren't on a plane and you need power to keep pushing the board up onto the bow wave. You have to turn the board with sail power, in a non-planing jibe.

So what does that have to do with downwinding boards? Same thing really. Planing is not something you "almost" do. There is a sharp transition, very obvious in windsurfing. Maybe less so with a downwind board. Pushing further up the bow wave is not semi-planing, it's just further up the resistance curve. The "release" that downwinding creates when you catch a bump is when you match your speed to the swell closely enough that there is a lot of energy being transfered from swell to board. What facilitates this energy transfer? Well, a lot of it is tail rocker. With some extremely rockered boards in short period, steep swell the boards can be almost stationary and still catch the bump. The reason is that the skin of the board conforms well to swell, causing maximum skin friction which is the medium that transfers energy from swell to board. Conversely, a rockerless tail with a planing surface is levered deep into the wave, lifting the nose, shortening the waterline, and minimizing the transfer of energy. Try to use your planing surfboard without a sail to catch waves and you you'll be amazed at how bad it is.

Next post I'll do the math. Right now I've got to go downwind. The gorge is nukin'.
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Bean

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Re: Will it Plane?
« Reply #1 on: June 29, 2016, 10:15:17 AM »
In one word, a word that everyone in the SUP community would recognize and understand, how would you describe board speeds exceeding displacement speed?   

Here is an interesting vid from Jim Terrell:

https://youtu.be/IkQWkOIkxpo
« Last Edit: June 29, 2016, 10:21:13 AM by Bean »

FloridaWindSUP

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Re: Will it Plane?
« Reply #2 on: June 29, 2016, 10:53:15 AM »
I have some experience with windsurfing my sups, and whether or not they plane.

http://jimbodouglass.blogspot.com/search?q=windsup

There seem to be three categories of sup-planing ability.

1) The ones that really do plane like a windsurf. What they have in common is a step-tail, which is a ~1" ledge about a foot ahead of the tail, which isolates a flat planing surface from the tail kick aft of the ledge. When the board planes, the section behind the ledge doesn't touch the water at all. The fin is forward of the ledge. This is what it's like on the Exocet Windsup 11'8 I bought from the store, and on the Angulo 10'4 where I added the flat rocker section and step myself and moved the fins forward.

2) The ones that plane, but inefficiently. I.e., if you apply enough sail power they will partially then totally climb over their bow wake and start scooting along at 12-20+ mph, but they're not too happy about it. This includes the surf style and race boards that have a drawn-out rockerline that's pretty flat for the last few feet of the board. For example, I put a mast track on my 14x27.25 Fanatic Falcon and I can get it going over 20 mph in flat water in a stiff breeze, but it throws an awkward rooster tail and feels unbalanced. 

3) The ones that are highly resistant to planing; where planing is essentially impossible, at least on flat water. This includes anything with too much rocker, especially too much tail rocker. Before I did the step-tail modification to my Angulo 10'4 it would definitely not plane on flat water.

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pdxmike

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Re: Will it Plane?
« Reply #3 on: June 29, 2016, 11:13:06 AM »
Planing? Displacement? Semi-planing?  I'm still trying to get past "heteroscedasticity".


TallDude

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Re: Will it Plane?
« Reply #4 on: June 29, 2016, 11:23:05 AM »
Planing? Displacement? Semi-planing?  I'm still trying to get past "heteroscedasticity".
And of course to support our lgtb paddlers we need to acknowledge the inverse " homoscedasticity". All things being equal.
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PonoBill

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Re: Will it Plane?
« Reply #5 on: June 29, 2016, 03:31:23 PM »
hetero or homoscedasticity aside, the planing surface of a windsurfer is fairly large. the reason is that the lift component has to fully support the weight of the rider and board. For many boats, and nearly all windsurfers, once the board transitions to planing the buoyancy component goes away--there is virtually no displacement, hence no buoyancy. It's ALL lift. The lifting force is applied over the area of the lifting plane. So one pound per square inch of lift applied to 100 square inches lifts 100 pounds. The more surface area available, the lower the maintenance speed is. Hulls in planing mode frequently "hunt", raising and lowering the bow. What's happening is the lift is raising the nose, and inertia carries it past the point where there is enough surface area exposed to provide the lifting force required. the nose settles, total lift increase, and it bobs back up.

A lot of things conspire to keep a rockered hull from planing well, and one of them is lifting area. When any curved surface is raised from contact with the water the area decreases as some exponential value based on the radius of the curve. There isn't a somewhat fixed flat surface for the lift to effect. If lift were dominant the area exposed to the lift varies rapidly, so the board gets very hard to control.

Much worse though is the approach to planing. With continuous rocker, any increase in lift decreases the waterline, which increases the resistance of the bow wave. Flat hulls can raise substantially in the water without losing waterline, so the bow wave resistance remains applied to the same wetted length. So with a curve rocker line, as you get closer to the bow wave, the rate of increase of resistance grows much more rapidly--the usual curve defined by froude limits goes exponential, but also the the waterline that determines that curve gets worse.

You CAN push a rockered hull into a plane, but it takes a lot of energy and it's helped by having a wave behind that conforms to the shape of the bottom. This creates a virtual flat spot that can offer a somewhat stable planing surface. But this is very dynamic and unstable.

The amount of energy that's required is substantial. We can derive a number mathematically, but the number used heuristically in boat design is 125 pounds per horsepower. and that's for a purpose-built planing hull. We can assume a higher number, but even in the best case, that means if you weigh 180 and your board weighs 20 you need two horsepower to get it out of the water.

As soon as I can get to it I'll derive how much power we're generally getting from the swells and waves we ride and how that power gets transferred to our boards.  But right now I have to get stuff ready to go race cars.

I'm really not trying to continue an argument about whether or not someone is really planing. If they want to believe they are, then that's nice. I'm laying out the information i have . I'd be very happy to see any discussion or information either supporting or blowing up what I'm trying to explain.
« Last Edit: June 29, 2016, 03:47:48 PM by PonoBill »
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PonoBill

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Re: Will it Plane?
« Reply #6 on: June 29, 2016, 04:49:35 PM »
In one word, a word that everyone in the SUP community would recognize and understand, how would you describe board speeds exceeding displacement speed?   

Hell, I don't know Bean, I'm not in charge of names. If I were we certainly wouldn't call these boards and what we do SUP. I never say that. Call it Beaning. Flatwater boards exceed "displacement speed" by which I assume you mean the froude "limit"--that's not called anything special, but from now on we can call it beaning. Catamarans go a lot faster than "displacement speed".  they Bean like crazy. That makes a lot more sense to me than incorrectly using a word that already has a specific mean throughout the water environment.

If you mean "matching board speed to an overtaking wave to transfer a large amount of energy and accelerate the board" then I'd call that surfing. But If you like we call that Blue Planeting. Or Fred.
« Last Edit: June 29, 2016, 04:52:59 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

blueplanetsurf

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Re: Will it Plane?
« Reply #7 on: June 29, 2016, 04:51:45 PM »
Thanks for moving this conversation to a new thread Bill, so we don't have to keep going off topic on the flatwater testing thread.

I appreciate your scientific approach but to me planing is something I feel.  Maybe planing is not the right word but to me there is only either displacement or planing, the transition is abrupt and you can feel it.   You are either pushing through the water or sliding on top of it, there is no in between state.

I have been windsurfing since the 80's so I'm very familiar with the difference between planing and not planing on a windsurfer.

You don't need a certain shape to plane.   I know that a wide, flat board board with no tail rocker and sharp rails like a formula slalom racing board will plane much earlier and easier than a rockered wave board but both boards will plane at speed.

I think this is an example most can relate to: think of a rock with rounded edges and a flat surface, it's certainly not designed to plane.  If thrown right though it will skip over the water and when it slows down too much to skip, it will often slide over the surface a bit before sinking.  It is too heavy to float, so it does not have a displacement mode, it can only plane or sink.  Once the dynamic lift created by the speed of it's flat surface moving over the water is less than the weight of the rock, it will sink. 

I don't think that you can reach planing speeds on flatwater, not even Connor.

With the help of of a waves or a good bump, a good downwind board will plane and slide over the surface of the water, with the weight supported mostly by the hydrostatic lift of the water underneath the board and not by the board's volume.  The faster you go, the further back you can move and the more you can reduce the wetted surface as more speed creates more lift and less surface area is needed to create the lift needed.  The board will keep sliding over the water until it slows down too much for the hydrostatic lift to support the weight of the paddler and the board drops back down into the water and goes back into displacement mode where the weight of the paddler and board are supported predominately by the volume of the board.  You can clearly feel the transition.   
I don't understand why you would not call it planing when most of the lift is created by hydrostatic lift.  If the rock sliding over the water is not planing, what do you call it?  If the skim boarder is not planing what do you call it? 




 
« Last Edit: June 29, 2016, 04:54:51 PM by blueplanetsurf »
Robert Stehlik
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Pierre

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Re: Will it Plane?
« Reply #8 on: June 29, 2016, 04:53:53 PM »
Thanks for all those explanations, Pono, I will add few ideas, theory and observation-based. Because if we cannot plane, we can try to get faster...
Indeed, a paddler on a SUP board cannot plane, some can reach an intermediate condition, the so-called "semi-planing" or "semi-displacement", which occurs at speed above hull speed, means their board's hull can create lift, which is not sufficient to counter all weight, but takes part of it, indeed nobody can reach it continuously, and it depends on design: a low-rockered hull with concave ( and some concave rocker below feet, some may guess which brand/model I am thinking about ;) ) which takes advantage of lightening and pop-up effect at paddle stroke.
another solution is to narrow and overspeed o a fisplacement mode by minimizing wetted surface and transverse wave system, like on a racing kayak or surfs or multi-hull, in that case hull resistance is much less at froude number a bit above hull speed... problem on a SUP board is stability so this method is marginal ( but has been tested see for example jim Terrel's experiences and designs)
Stabilizing method for such narrow low wetted surface design can be either outriggers or hydrofoils, or both.. it can work, even this is not SUP as we use to see.

Hydrofoils is another artefact which make buzz in DW condition, but needs to be better considered in flat water, I dream about a SUP board/ aquaskipper ( or Pumpabike) hybrid design... why not, there is a "pop-up" effect with paddle stroke, so...

Whatever the way we may take to break out speed limit, we face another limitation, which is propulsion, not only POWER but speed: the fastest, the higher paddle frequency we must keep...

Personally, I search the way of minimizing friction by lengthening ( a bit) and narrowing hulls, but also reducing wetted surface. it works, not so stable but it works and ESPECIALLY on smooth DW conditions; and guarantees a low drag and low power need at speeds around "Froude barrier"...  an option to make thing stable is under preparation.
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PonoBill

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Re: Will it Plane?
« Reply #9 on: June 29, 2016, 04:56:34 PM »
Skipping. and you might be surprised to know that a skipping rock doesn't skip on one surface in the water--it doesn't "plane" at all. The trailing edge hits first and pivots the rock over, then the leading edge catches and throws the rock clear of the surface. It drills a cavity in the surface and then rises up the steep face of the cavity.  It flips over with each skip. Probably not what you think of as planing, though in the video they use that term. Oh well. High speed rock video at 1:30.

Here's a little paper on it: http://arxiv.org/PS_cache/physics/pdf/0210/0210015v1.pdf and a video:
https://www.youtube.com/watch?v=9ocg__QFVEc
« Last Edit: June 29, 2016, 05:18:14 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

leecea

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Re: Will it Plane?
« Reply #10 on: June 29, 2016, 05:09:10 PM »
Quote
Catamarans...they Bean like crazy

If my foot ever heals and I get the Hobie out again, I can tell people I was at the lake beaning the Cat  :-\
« Last Edit: June 29, 2016, 05:10:44 PM by leecea »

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Re: Will it Plane?
« Reply #11 on: June 29, 2016, 05:11:49 PM »
Skipping. and you might be surprised to know that a skipping rock doesn't skip on one surface in the water--it doesn't "plane" at all. The trailing edge hits first and pivots the rock over, then the leading edge catches and throws the rock clear of the surface. It flips over with each skip. Probably not what you think of as planing.

Ok, so let's say the rock is skipping, not planing (it does not however flip over with each skip). What about the skim boarder, what do you call that?
« Last Edit: June 29, 2016, 05:13:32 PM by blueplanetsurf »
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PonoBill

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Re: Will it Plane?
« Reply #12 on: June 29, 2016, 05:22:50 PM »
skim boarders are absolutely planing. Held up almost exclusively by lift. Flat surface, minimal buoyancy. Planing for sure. So are Paipos. Sims went so far in trying to ensure his boards were planing that he built them with very low buoyancy. It's never been clear to me whether he thought decreasing buoyancy would increase lift, or if he just thought it would be more certain that he was reaching the transition to planing. Smart guy, I'm sure he knew that the amount of lift available is a function of area and speed. 

I'm not sure what that disc is or what it's doing. With a very high spin rate you don't get a flip, but look at the video of a rock being skipped and you can see the flip.
« Last Edit: June 29, 2016, 05:24:43 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

blueplanetsurf

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Re: Will it Plane?
« Reply #13 on: June 29, 2016, 06:03:28 PM »
http://www.storerboatplans.com/wp/design/planing-is-bunkum-myths-about-planing-displacement-and-semi-planing-hulls-and-modes/

I mostly agree with this guy's thinking, he concludes:

Water displaced + dynamic lift = total weight of boat, gear and crew.
or
planing force + displacement = total weight

So “planing” is something that belongs in descriptive language rather than being a technical term. Like saying the moon is “golden”. So it can still be used for something you experience … but it is something that just can’t exist in a 100% pure form …

… because if it did … the boat would not be touching the water at all … so could not develop “planing lift” from the water.
Robert Stehlik
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mrbig

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Re: Will it Plane?
« Reply #14 on: June 29, 2016, 07:22:52 PM »
Bad hyperlink..I'll  try to fixit.
« Last Edit: June 29, 2016, 07:26:41 PM by mrbig »
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