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Surfing vs. Plaining


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How do you separate surfing vs. plaining? Over here the ocean swell runs at approximately ~ 14 knots.  In blue water  you hear that number often. To me, if your boat speed/swell speed is similar, you are "surfing". When you start launching into the backs of waves in front of you, you are "getting on the step". My Moore definitely lights it up downwind, to the speed of the swell, even under reduced plain sail, but in flat water bursts up to wind speed are great and fun, but short lived... Where do you guys make the distinction??

 

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For me, an ultra simplistic separation is that planing (not plaining ;)) is solely achieved through hydrodynamic actions acting to lift the hull.

If there is any gravity component, ie a small wave, chop, bump or such, then it's surfing.

Surfing can often initiate planing but that to me is still surfing.

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An 86ft power boat can plane with the big diesels cranked up.

The same boat can surf when just in gear and the waves are smashing into the aft doors. It stops surfing when the bow is deep enough in the back of the wave in front...

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18 minutes ago, Jethrow said:

 

Surfing can often initiate planing but that to me is still surfing.

Yep, a Laser can plan because of the SA/Disp ratio.  A displacement boat may need a push but one on a plane a good driver can milk it.

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You can plane is flat water...

You need waves to surf...

If you are going faster than the waves you are planing,

if you are moving about at the wave's speed, and staying on the same wave for a while you are surfing.

 

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If you get a push from a wave to start you are surfing.  It then becomes a matter of how long you can maintain the surf before she drops back into the water.

My personal record was in about 30 knots of NE heading for Hobart in 89 or 90 on a 42 foot cruiser racer.  3 waves.  Got thrown by a big 1st one continued surfing up the back of the second and over the top which gave us enough momentum to climb over the third one and ride it to the bottom.  Surprisingly this was all done at 21 -22 knots so never got particularly fast,  just got lucky with the swell pattern.   We managed 2 waves 3 or 4 times that evening,  so it was an unusual swell.

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2 hours ago, TUBBY said:

If you get a push from a wave to start you are surfing.  It then becomes a matter of how long you can maintain the surf before she drops back into the water.

My personal record was in about 30 knots of NE heading for Hobart in 89 or 90 on a 42 foot cruiser racer.  3 waves.  Got thrown by a big 1st one continued surfing up the back of the second and over the top which gave us enough momentum to climb over the third one and ride it to the bottom.  Surprisingly this was all done at 21 -22 knots so never got particularly fast,  just got lucky with the swell pattern.   We managed 2 waves 3 or 4 times that evening,  so it was an unusual swell.

So you are also saying that when a surfer catches a wave his little board is not planing? Yes he uses the waves to get the initial push, but it sure looks like the board is planing.

1 hour ago, Chris in Santa Cruz, CA said:

I have been on boats where a swell instigates planing and then the boat proceeds to go faster than the waves until wind apparent wind pressure drops below the threshold needed to maintain the plane.

Yep, it almost feels like you are on Ice or on snow skis. The verge of control has been hit and it can be scary fast.

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Seems impossible for a hull in displacement mode — hull speed limited — to stay with a wave. The boat’s immersed waterline would need to be the same as the distance between wave crests. So surfing on a wave face requires planing mode.

Some confusion may arise because heavy boats on a plane still displace a great amount of water. A powerful cabin cruiser for example. 

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2 hours ago, Borracho said:

Seems impossible for a hull in displacement mode — hull speed limited — to stay with a wave. The boat’s immersed waterline would need to be the same as the distance between wave crests. So surfing on a wave face requires planing mode.

Some confusion may arise because heavy boats on a plane still displace a great amount of water. A powerful cabin cruiser for example. 

Not quite true. First of all no such thing as hull speed. Second. All it takes is power. A big wave the slope of the wave suffices to provide the power.

A 3o foot sailboat can and will sirf the wake of a 45 footers. Even old tymie boats

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With my Olson 29, 30 knots wind and 10-15' waves, boat speed peaking above 16 knots we were exceeding the speed of the wave and driving into the back of the next wave(if you've ever been on an O29 in these conditions, we are talking burying the bow in the next wave). Was I surfing or planing?

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Thank you all for the clear and concise responses. They allow me to hone in and clarify my inquiry. Obviously dinghies & multi-hulls have different parameters for "surfing vs. planing", and to muddy the water, (sorry for the pun), there is now so much development in lifting foils, T-foils, hull shape and stability that our very basis for what is "hull speed" may not be so clear anymore. Good possibility I am wrong but I believe in the era of the age of sail up to and including the clipper ships, hull speed was determined to be the square of the weighted waterline length, as the twentieth century progressed it became 1.34 the square of the WWL. Love them or hate them, the America's Cup T-foilers WWL has absolutely nothing to do with hull speed, and they are in flat water. Obviously they are not surfing but are they really planing? Are they just an anomaly? Do we just sort them into a range of their own, (not dingy, not multi-hull, developmental?). The wakeboarding video's bring out a part of this. Notice the difference in the length of the different boards. In the 1st video the board on the outside is noticeably longer and the guy is just cruising, the others are shorter and obviously more responsive but kinda need to be "worked" to stay on the wake. Then you have the foiler who can go faster than the boat creating the wake, until he runs out of wake. When I'm at the helm of my boat I'm more like the guy with the long board, my younger crew are much more aggressive on the helm, knowledgeable pumping of the sails seems to help us all out equally. 

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Well...hull speed is definitely a real thing, @fastyacht.. It is defined as the speed at which the wavelength of a boat's bow wave equals the waterline length of the vessel. The value  does not vary except with waterline length except for a tiny amount due to water salinity and. The incremental amount of energy to increase the vessel speed beyond the hull speed varies with the characteristics of the boat. However in engineering, it is now (for 200 years?) replaced by the more scientific Froude Number.

Planing is defined as the mode where hydrodynamic lift overtakes buoyancy (hydrostatic lift). Surfing is being propelled by a steep or breaking wave without regard to planing. Surfboards are always planing while surfing. Waves in the open ocean are unable to accelerate a floating object unless somehow steepened. A floating ball will not roll down the face of even a huge ocean swell, for example. Nor do boats change speed in such seas. Steepening can be from entering shallower water or from being driven by wind. Heavy slow boats entering a channel with following seas often surf for a moment, without planing, just before embarrassing themselves. In heavy following seas heavy displacement boats will surge somewhat beyond hull speed. Such boats tend to just create more wave drag until they either slow down or sink bcuz hydrodynamic lift never overcomes buoyancy. So the thread title Surfing vs. Planing is improper. Surfing and Planing would be better.

I don't think one can plane at less than hull speed. The water moves out of the way, around the hull, rather than producing any upwards force. 

As a boat begins planing the wave-making drag is reduced. For some boats the wave-making drag is already small so there is not much difference at the transition to planing. 

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2 hours ago, inneedofadvice said:

With my Olson 29, 30 knots wind and 10-15' waves, boat speed peaking above 16 knots we were exceeding the speed of the wave and driving into the back of the next wave(if you've ever been on an O29 in these conditions, we are talking burying the bow in the next wave). Was I surfing or planing?

You were having fun.

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4 hours ago, inneedofadvice said:

With my Olson 29, 30 knots wind and 10-15' waves, boat speed peaking above 16 knots we were exceeding the speed of the wave and driving into the back of the next wave(if you've ever been on an O29 in these conditions, we are talking burying the bow in the next wave). Was I surfing or planing?

Surfing, planing, and submarining. Big fun. Can get crowded in the back of the boat. 

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This discussion promotes a false dichotomy - it is not either surfing or planing. 

Boats can surf without planing, or plane without surfing. Boats can plane while surfing. There is an overlap between surfing and planing.

On a planing hull (or board), once you exceed your hull speed (so long as you aren't foiling), you are planing.

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2 hours ago, Borracho said:

Surfing, planing, and submarining. Big fun. Can get crowded in the back of the boat. 

Already told my sons we would be crowded in either the port or starboard stern quarter when flying the chute on the hotfoot 20. 

550 lbs on a boat like that is statistically meaningful :)

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21 minutes ago, Bruce Hudson said:

This discussion promotes a false dichotomy - it is not either surfing or planing. 

Boats can surf without planing, or plane without surfing. Boats can plane while surfing. There is an overlap between surfing and planing.

On a planing hull (or board), once you exceed your hull speed (so long as you aren't foiling), you are planing.

bravo, sir, for ending our mildly entertaining circle jerk

hope you're happy with yourself :)

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18 minutes ago, Chris in Santa Cruz, CA said:

Already told my sons we would be crowded in either the port or starboard stern quarter when flying the chute on the hotfoot 20. 

550 lbs on a boat like that is statistically meaningful :)

Have them watch for kelp patches while back there. I recall a collision with kelp ahead of a very rare black squall was the demise of the Hotfoot down in Monterey. Still on the bottom I assume. Many years ago. 

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5 hours ago, Borracho said:

As a boat begins planing the wave-making drag is reduced. For some boats the wave-making drag is already small so there is not much difference at the transition to planing

Thanks Borrachio, that was all very informative and succinct, nicely put.  The 12.50 had a lurch onto the plane, smooth but it was there. Makes sense with a flat transom. 

We forgot one thing, noise. Surfing is noisy, planing is not ...well, at least till you get up into the teens and the harmonising starts. But prior to that, it amazes me how quiet everything becomes. Sounds more like a muted radio hiss than water.   

 

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In the dinghy world defining planing is an old argument. The powerboat boys don't reckon they are planing properly until they are at about 3 x root L, which precious few sailboats are capable of. Truth is, it is, to borrow the trendy phrase of the time, a spectrum. At 0.1 root L knots boats are pretty much 100% displacement, at 3x root L predominantly dynamically supported, in between its pretty much impossible to draw a rational) line. Sufficiently light boats can have significant dynamic support well below "Hull speed", and sufficiently narrow boats very little dynamic support well above that point. In any case "Hull speed" is an approximation anyway, not a boundary. The "Hull speed" of a low prismatic and high prismatic boat of the same nominal length will be subtly different. 

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12 hours ago, Borracho said:

Well...hull speed is definitely a real thing, @fastyacht.. It is defined as the speed at which the wavelength of a boat's bow wave equals the waterline length of the vessel. The value  does not vary except with waterline length except for a tiny amount due to water salinity and. The incremental amount of energy to increase the vessel speed beyond the hull speed varies with the characteristics of the boat. However in engineering, it is now (for 200 years?) replaced by the more scientific Froude Number.

Planing is defined as the mode where hydrodynamic lift overtakes buoyancy (hydrostatic lift). Surfing is being propelled by a steep or breaking wave without regard to planing. Surfboards are always planing while surfing. Waves in the open ocean are unable to accelerate a floating object unless somehow steepened. A floating ball will not roll down the face of even a huge ocean swell, for example. Nor do boats change speed in such seas. Steepening can be from entering shallower water or from being driven by wind. Heavy slow boats entering a channel with following seas often surf for a moment, without planing, just before embarrassing themselves. In heavy following seas heavy displacement boats will surge somewhat beyond hull speed. Such boats tend to just create more wave drag until they either slow down or sink bcuz hydrodynamic lift never overcomes buoyancy. So the thread title Surfing vs. Planing is improper. Surfing and Planing would be better.

I don't think one can plane at less than hull speed. The water moves out of the way, around the hull, rather than producing any upwards force. 

As a boat begins planing the wave-making drag is reduced. For some boats the wave-making drag is already small so there is not much difference at the transition to planing. 

Hull speed is a fixation in peoples brains. There is no such thing except as a convenient abstraction.

But glad you enjoyed writing all that. I concur substantially on the rest.

Froude number has nothing to do with hull soeed. It is merely the nondimentional ratio of vessel speed to a reference dimension. The reference can be length, depth etc. Many intetesting curves have been drawn using it. The principle importance being similitude.

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Just now, fastyacht said:

Jim brought up the effects of dispkacement vs kength. This is really, along with prismatics and buttock shspe, why I make fun of "hill speed"

( There is domrtiing misleading in there about dynamic lift though). I have never seen any way to acheive dynamic lift at Fn less than0.4 except eith foils. In fact vrssels even loght develoo suction and bow down trim at Fn lrss than 0.4

:^D

 

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41 minutes ago, fastyacht said:
44 minutes ago, fastyacht said:

Jim brought up the effects of dispkacement vs kength. This is really, along with prismatics and buttock shspe, why I make fun of "hill speed"

( There is domrtiing misleading in there about dynamic lift though). I have never seen any way to acheive dynamic lift at Fn less than0.4 except eith foils. In fact vrssels even loght develoo suction and bow down trim at Fn lrss than 0.4

:^D

 

Is "foiling" a subset of planing?

"Dynamic lift" is kind of a clumsy and inexact phrase. Water being incompressible, i assume we can't really postulate a high-pressure region of water pushing a planing hull upward. We -can- postulate that a hull may be moving so fast that the inertia of the water it has to push downward to go by, is greater than the weight of the hull & it's contents....

FB- Doug

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Surfing can take place underwater just ask all the dolphins and seals out there. There does not have to be a gravity component. If you have ever bodysurfed and done an underwater takeoff, you know what I'm saying.

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22 minutes ago, Steam Flyer said:

Is "foiling" a subset of planing?

"Dynamic lift" is kind of a clumsy and inexact phrase. Water being incompressible, i assume we can't really postulate a high-pressure region of water pushing a planing hull upward. We -can- postulate that a hull may be moving so fast that the inertia of the water it has to push downward to go by, is greater than the weight of the hull & it's contents....

FB- Doug

Coprdssibility is not the issue.

The classical  thing is measuring cg rise. At below Fn 0.4 (wave speed of hull wl) the cg actually falls due to suck. As you get on the back of the bow wave you are still not lifted therefore classically not planing.

From a thought experiment standpoint iti s semantics. "Chines dry" is another planing idealisation. For thought experiment can you have that without maximum cg rise? (The answer varies because of tricks!)

The whole subject is slippery lol

 

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35 minutes ago, fastyacht said:

Coprdssibility is not the issue.

The classical  thing is measuring cg rise. At below Fn 0.4 (wave speed of hull wl) the cg actually falls due to suck. As you get on the back of the bow wave you are still not lifted therefore classically not planing.

From a thought experiment standpoint iti s semantics. "Chines dry" is another planing idealisation. For thought experiment can you have that without maximum cg rise? (The answer varies because of tricks!)

The whole subject is slippery lol

 

OK, this is intriguing but I don't really understand. CG rise and fall? Chinese dry?

And yes, slippery subject, fraught with old wives tales and misinfo, such as the pernicious lie that Flying Scots and J105s can plane......................

FB- Doug

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The "suck" reaches it maximunm somwhat past hull speed when the boat is "digging a hole"

Like I said before, this sucking down begins below hull dpeed. (Really all the way from zero)...there are interesting interferenceceffects with wavevpositons rhat affect a hull floating level...when crest at fattest part of boatvit lifts...hydrostatically....trough loewrres it...

In a planing hull you fo not even get back to normal hydroststic cg position until somewhere around Fn 0.7

Whoch is more that 1.5 times "hull speed."

Jim points out that "planing" to  dinghy sailors aint planing. Certainly no such thing as upwind planing haha unless you are a 49er or aedeen

As for surfing. Yes.

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Lifelong surfer and multi sailor here.  On most multis you can surf all day with not much planing going on.  On my Weta, off the wind, it's nothing but planing whether surfing or not.  Super flat skiff-like main hull, the amas rarely touch the water.  Very different feeling from other multis.  

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On 6/9/2021 at 8:33 PM, Moore Play said:

How do you separate surfing vs. plaining? Over here the ocean swell runs at approximately ~ 14 knots.  In blue water  you hear that number often. To me, if your boat speed/swell speed is similar, you are "surfing". When you start launching into the backs of waves in front of you, you are "getting on the step". My Moore definitely lights it up downwind, to the speed of the swell, even under reduced plain sail, but in flat water bursts up to wind speed are great and fun, but short lived... Where do you guys make the distinction??

 

You know when you are surfing - it's self evident.  The boat will take a nose down attitude, and 'slide' along the face of the wave.  You will be traveling at the same speed AS the wave.

If you're planing, it's unlikely you are traveling the same speed as the waves, unless they are so large that you can't plane up and over the face of the one in front of you.

They are two pretty obvious different things.

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3 hours ago, fastyacht said:

Hull speed is a fixation in peoples brains. There is no such thing except as a convenient abstraction.

But glad you enjoyed writing all that. I concur substantially on the rest.

Froude number has nothing to do with hull soeed. It is merely the nondimentional ratio of vessel speed to a reference dimension. The reference can be length, depth etc. Many intetesting curves have been drawn using it. The principle importance being similitude.

Heh. In my professional opinion, you should get back to use when sober :-) After merely downloading Grammerly.

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2 hours ago, fastyacht said:

So if "hull speed" is a "thing" why is there a smooth curve? And where on it do you put the defined point?Yes this is arhetorical question

You guys are arguing at cross purposes.

Hull speed is a thing, it's is a well defined velocity and can be calculated for any hull, it's the speed at which the wavelength of the bow wave is equal to the waterline length.

BUT it's just a number, if doesn't  necessarily have a physical effect. The fact that there is no hump of bump is irrelevant.

The whole point about the hull speed is that it was a very cool (early) example of the power of non dimensional quantities. A chart of resistance vs velocity is much less use than a chart where the abscissa is velocity/hull speed, as you demonstrate in the fig 8 chart you show.

In fact the two charts you show are a great way of showing the power of a concept like hull speed. (As long as we don't claims about it being a barrier between displacement mode and planing etc.)

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16 hours ago, Bruce Hudson said:

This discussion promotes a false dichotomy - it is not either surfing or planing. 

Boats can surf without planing, or plane without surfing. Boats can plane while surfing. There is an overlap between surfing and planing.

On a planing hull (or board), once you exceed your hull speed (so long as you aren't foiling), you are planing.

I've been told that my boat has a Zero Step Planing Hull. That little flat spot in the bow goes all the way back to the stern. And I swear I have planed at least once, the boat felt like it was on ice and not connected to the water at all.

Zap26_1600.thumb.jpg.37028e47aff9b2867fdd5adc270dd9da.jpg

 

As for the submarining discussion. Here is the greatest shot of them all. Can you imagine the load on the backstay?

merlin_submarine.jpg.767acd051bc27d256afb3fbb52c28085.jpg

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On 6/9/2021 at 6:18 PM, LionessRacing said:

 

If you are going faster than the waves you are planing,

if you are moving about at the wave's speed, and staying on the same wave for a while you are surfing.

 

there's no context here. technically (and what else matters), if a Moore 24 which planes at about 9 knots boat speed is surfing a wave at nine+ knots, it's planing. the real surfing happens on a plane.

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18 minutes ago, 3to1 said:

there's no context here. technically (and what else matters), if a Moore 24 which planes at about 9 knots boat speed is surfing a wave at nine+ knots, it's planing. the real surfing happens on a plane.

I have surfed on a Bullseye. 5 nm in 40 minutrs flat. Surfing not planing

Ive surfed a 30 foot wl CCA boat in 15 foot waves. 36 nm in 4 hours. Surfing not planing.

Yoi do not have to plane to be surfi g

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14 minutes ago, fastyacht said:

I have surfed on a Bullseye. 5 nm in 40 minutrs flat. Surfing not planing

Ive surfed a 30 foot wl CCA boat in 15 foot waves. 36 nm in 4 hours. Surfing not planing.

Yoi do not have to plane to be surfi g

I din't say you need to be planing to be surfing, depends on a boats D/L ratio. but it helps

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First time I surfed while not planning was on a Hobie 14.  They surf a wave while still in the water.  Same for big cats and it's nothing to do with multihull, as pointed out ^ it's the D/L ratio.

On  monohull, the helm changes when on the plane.  It goes neutral on boats I have steered and the mast straightens up as the drag on the hull decreases.  You know it when it happens. 

 

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I like the feeling of planing as you're sailing more on the keel and rudder, whereas the hull come into it more when you're just surfing. 

Snaking downwind on the plane you can easily feel the influence of a change to the angle of attack of the keel, and then the resultant lift. Awesome fun. 

  

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The Gov't, including the CG, has definitions for most anything. Someplace I once saw a definition of planing based on what is holding the boat up. At rest or when moving slowly, the boat is supported by buoyancy which is static water pressure.  At speed, the boat may be supported by dynamic pressure which is caused by the moving boat running into water molecules.  

The definition was that you are planing when the total dynamic pressure is more than 50% the weight of the boat. 

An old yachtman's definition was that you are planing when the boat separates from the stern wave.

Back in the 50s or 60s, it was taken for granted that a keel boat couldn't plane. This caused controversy when boats with knotmeters started reporting exceeding hull speed when surfing down waves. I remember explanations involving the circular motion of molecules in waves. Eventually,  enough boats went fast enough often enough to settle the matter.

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17 hours ago, Grrr... said:

You know when you are surfing - it's self evident.  The boat will take a nose down attitude, and 'slide' along the face of the wave.  You will be traveling at the same speed AS the wave.

Yeah nah.

I can think of many instances where the boat speed is faster than the wave speed, planing or not. Most times, the direction you want to go, is not exactly the same as the wave, and you can surf along the caught wave. This is evident with surfers.

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16 hours ago, 3to1 said:

there's no context here. technically (and what else matters), if a Moore 24 which planes at about 9 knots boat speed is surfing a wave at nine+ knots, it's planing. the real surfing happens on a plane.

There's no meaning here... ( and that should matter)

A Moore 24 and other ULDB such as 49er dinghys can sail fast enough to climb over their bow wave and plane off in flat water. They don't need waves from astern to lift them up, so that they can slide downhill. Foiling boats are an extreme planing example where they lift out of the water, and are not limited by the displacement wave making drag.

"Lioness" at 20,000 lbs and a short CCA yawl Rig darn sure won't plane, as we approach hull speed of 8.5 kts (beam reach > 25kts TWS) ripping a large hole in the water,  the roaring of the building quarter wave is quite impressive, and it will flatten on coming waves quite nicely.

We have surfed, at over 9 kts in relatively short bursts down wind, lifted up by a > 6' wave and sliding down it's face, much like any other surfing object. 

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3 hours ago, Bruce Hudson said:

Yeah nah.

I can think of many instances where the boat speed is faster than the wave speed, planing or not. Most times, the direction you want to go, is not exactly the same as the wave, and you can surf along the caught wave. This is evident with surfers.

And you remain on the face of the wave.  With big enough waves, you can surf down until you hit the wave face, but you aren't gonna go faster in the same direction as the wave than the wave speed.  You're being a little pedantic when you start arguing relative directions.

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22 hours ago, SemiSalt said:

An old yachtman's definition was that you are planing when the boat separates from the stern wave.

This is what I was taught back in the 60s and still check for now.

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44 minutes ago, Autonomous said:

So if I get a Westsail 32...

I'm plotting out a passage from Lake Ontario to Lake Erie. There is at least one opportunity to dramatically exceed hull speed and get the entire keel out of the water.

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One of the most noticeable differences between "surfing" on a surfboard, body board or body surfing at a surf break and, surfing on a boat on open water swells, (uh-oh swell vs. wave discussion forthcoming), is the shape and length of the wave/swell.  Unless it is a sandy bottom you generally find the peak where the wave starts to break due to the shape and depth of the bottom and you catch the wave where and when the face steepens, There is a sweet spot where the swell changes from rolling underneath you and not actually moving the water to breaking and becoming a moving mass of water, this sweet spot is where you want to place your board or body to catch the wave. You can really feel it when you are body surfing as the face of the wave grows to about double the size of the swell, if you nail that spot one or two good strokes or kicks and shazam you are up and in the wave.

On a sailboat in ocean swells even if the size and condition generate a form of a "breaking" wave the swell continues to roll on with or without you and while ocean swells can develop faces and breaks but they rarely break top to bottom or line up in an organized fashion. Therefore the mechanics of board or body surfing are different in quite a few ways. Way way overly simplified, on a surfboard and near shore break you are mostly riding the face of a breaking wave that was generated by a swell. on a sailboat the energy that gives you lift and speed is more from the swell than the face, although most often you do need some steepness or a good sail pump to get the fun started

 

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12 hours ago, Grrr... said:

And you remain on the face of the wave.  With big enough waves, you can surf down until you hit the wave face, but you aren't gonna go faster in the same direction as the wave than the wave speed.  You're being a little pedantic when you start arguing relative directions.

I read some guy's prediction that speeds for the southern ocean leg of an around the world race will not exceed wave speeds. Too much energy required to climb up the back of a wave ahead of you. Don't know if that has proven true.

 

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28 minutes ago, SemiSalt said:

I read some guy's prediction that speeds for the southern ocean leg of an around the world race will not exceed wave speeds. Too much energy required to climb up the back of a wave ahead of you. Don't know if that has proven true.

 

Of course it is proven true. Look at the wave spectra. Nobody has averaged wave speed ever down there.

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1 hour ago, fastyacht said:

Of course it is proven true. Look at the wave spectra. Nobody has averaged wave speed ever down there.

Including the US Navy.

 

6 hours ago, unShirley said:

This is what I was taught back in the 60s and still check for now.

Maybe for old IMS, IOR or CCA warhorses.  Not for modern boats. 

My boat regularly leaves it's stern wake behind, with a straight clean exit from the transom and a small roostertail 2 - 5 meters back.  When that happens, we are going fast.  We are zipping right along in speedy displacement mode at maybe 12-15 knots.  But we are not "planing.  When we break loose and get hydrodynamic lift up out of the water, we are planing.  This can happen in relatively flat water with wind-driven chop too small to surf on, but it takes us about 25 knots to get up and out.  Then the speeds get up into the high teens - low 20s. 

Watch video of the SuperSeries TP52s at the middle range of at about 15-18 k TWS.  Their stern wake has well separated.  They are speedy but in displacement mode.  Then watch at the upper end of their permitted wind range of about 22-25 knots...they are bow up and planing.

 

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1 minute ago, 3to1 said:

fair enough, my statement was a little black/white.

I shouldn't be so short.   But supply enough energy to the order of rho vee squared and anything can exceed "hull speed" without necessarily planing. 

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This is really a discussion about drag.  A displacement boat surfing down a wave is still experiencing a significant amount of drag.  That's why so much water is being moved (large bow wave).  The boat may be going 14 knots, but it is still in a high drag region, and in a displacement mode.

A planning boat has seen a reduction in drag (due to a change in hydrodynamic lift vs drag) which allows the boat to accelerate given the same amount of power.  

My Boston Whaler 110 Sport is a great example.  With three people on board, sitting in the normal seats/positions, the 25 hp outboard can not push the boat on to a plane and accelerate beyond about 10 knots.  It's stuck in a displacement mode, pulling a huge stern wave even at full power for an extended period of time.  Move a person forward to sit up on the bow, and you change the trim (and angle of attack of the hull) and the boat will accelerate up on onto a plane with no increase in the amount of thrust the engine is providing (yes, the thrust angle does change some which helps, but no amount of engine trim will get the boat onto plane without weight distribution change).

Planning occurs when hydrodynamic lift results in a reduction of drag, and allows the boat to accelerate well beyond hull speed with no increase in the thrust the engine (sails) is/are providing

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On 6/11/2021 at 11:52 PM, SemiSalt said:

Back in the 50s or 60s, it was taken for granted that a keel boat couldn't plane. This caused controversy when boats with knotmeters started reporting exceeding hull speed when surfing down waves. I remember explanations involving the circular motion of molecules in waves. Eventually,  enough boats went fast enough often enough to settle the matter.

So how did they explain the 1951-built Huff?  Was that also somehow not-planing?

https://www.nationalhistoricships.org.uk/page/shipshape/huff-arklow-restoration

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6 hours ago, Crash said:

This is really a discussion about drag.  A displacement boat surfing down a wave is still experiencing a significant amount of drag.  That's why so much water is being moved (large bow wave).  The boat may be going 14 knots, but it is still in a high drag region, and in a displacement mode.

A planning boat has seen a reduction in drag (due to a change in hydrodynamic lift vs drag) which allows the boat to accelerate given the same amount of power.  

My Boston Whaler 110 Sport is a great example.  With three people on board, sitting in the normal seats/positions, the 25 hp outboard can not push the boat on to a plane and accelerate beyond about 10 knots.  It's stuck in a displacement mode, pulling a huge stern wave even at full power for an extended period of time.  Move a person forward to sit up on the bow, and you change the trim (and angle of attack of the hull) and the boat will accelerate up on onto a plane with no increase in the amount of thrust the engine is providing (yes, the thrust angle does change some which helps, but no amount of engine trim will get the boat onto plane without weight distribution change).

Planning occurs when hydrodynamic lift results in a reduction of drag, and allows the boat to accelerate well beyond hull speed with no increase in the thrust the engine (sails) is/are providing

When I was a kid I spent hours experimenting with a heavy flattie with a 6 hp evinrude. Fortunately it had stiff steering bearings so I'd do what you describe but all alone. Up to the bow, waterline lenghtens, speed (displacement) increases, stay up there and she starts to plane. Then I could come aft some and go faster, then all the way back and she would fall off the plane again.

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4 hours ago, TwoLegged said:

So how did they explain the 1951-built Huff?  Was that also somehow not-planing?

https://www.nationalhistoricships.org.uk/page/shipshape/huff-arklow-restoration

There were other light displacement boats back then too. Laurent Giles did a number of them--won the Fastnet before the 50s. And prewar the 22 sq meters would go into the teens downwind. Also the sonder boats would roar, as would our scows, and RELIANCE was described as a "skimming dish" hahaha.

 

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13 hours ago, Left Shift said:
19 hours ago, unShirley said:

This is what I was taught back in the 60s and still check for now.

Maybe for old IMS, IOR or CCA warhorses.  Not for modern boats. 

My boat regularly leaves it's stern wake behind, with a straight clean exit from the transom and a small roostertail 2 - 5 meters back.  When that happens, we are going fast.  We are zipping right along in speedy displacement mode at maybe 12-15 knots.  But we are not "planing.  When we break loose and get hydrodynamic lift up out of the water, we are planing.  This can happen in relatively flat water with wind-driven chop too small to surf on, but it takes us about 25 knots to get up and out.  Then the speeds get up into the high teens - low 20s. 

Watch video of the SuperSeries TP52s at the middle range of at about 15-18 k TWS.  Their stern wake has well separated.  They are speedy but in displacement mode.  Then watch at the upper end of their permitted wind range of about 22-25 knots...they are bow up and planing.

Back in the 60s I was a kid sailing an FJ, or on a Kite, 420, 505, etc.  So, my comment (regarding agreeing that planing was determined by the stern wake moving away from the transom) was relative to planing dinghys.  Now that I am in my golden years, I have reverted to my dinghy days, albeit with training wheels, by sailing a Weta.  The Weta main hull is like a skinny planing dinghy, so I still occasionally look down to see where the water is exiting the transom to determine if the main hull is planing or not.  Regardless of this discussion and the accuracy of my perception, it keeps me entertained.

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On 6/11/2021 at 3:49 PM, shaggybaxter said:

I like the feeling of planing as you're sailing more on the keel and rudder, whereas the hull come into it more when you're just surfing. 

Snaking downwind on the plane you can easily feel the influence of a change to the angle of attack of the keel, and then the resultant lift. Awesome fun. 

  

For me surfing some  bigger monohulls is doable downwind in large long period swells with brisk winds.  An optimal boat will have a canoe bottom, light displacement, huge SA/DISP ratio,  efficient keel and a high aspect ratio spade rudder.

For example, we were able to surf a Santa Cruz 52 in the right open ocean conditions, typically a 15+' DDW swell with a 10-15 second period & 20-25kn winds.  The key is once you get a boost off a crest, instead of going DDW head up and keep the sails driving, i.e. surf across the wave instead of down it.  You can convert a 15 second 15kn surf into a monster 45 second surf with only a 20°+- course change.  We're talking sustained 20-25kn boatspeeds.  If the swell is not DDW, there'll be a favored gybe where you can stay on the downslope part of the swell for minutes at a time with massive speed.

Doing this is difficult and requires topnotch crew and gear.  Key is the driver, who controls the "snaking" path of the boat, not too low & slow, not too high & fast with a bad VMG, main thing is to stay on the swell as much a possible; really good surfboarders have the knack and patzers like me were never allowed to helm.  The trimmers have react quickly and correctly to apparent wind velocity changes and grinders have to be rotated often.  Everybody else is on the high side behind the helmsman.  Probably best to use the 1.5 ounce kite because mistakes will happen and blowing up a kite is slow.  Some boats have a "chicken chute" which is a few feet short on the luff with narrower shoulders so is controlled more easily and there's less chance of the pole catching the water.

Exiting a surf correctly is mission critical.  Once you hit the trough you'll massively slow down and if you don't turn down to hit the crest perpendicularly and trim the sails to a DDW configuration bad things can happen like rolling the boat to where the leeward spreader is immersed.  The idea is to punch through the crest and be ready for another surfing run without losing control.

Although fun and fast there's lots of downsides to this downwind style.  It's very wet at speed with bow waves roostering into the cockpit and a bad crest transition can submarine the bow to where there's 3 feet of water rushing over the decks, overloading the rig and threatening a MOB situation if a crew is caught unawares.  It's very tiring for the crew to stay on edge and keep pushing for hours.  It's hard on gear.  But the dividends if done correctly are enormous, we won a few 100 mile offshore races by over an hour corrected against  boats who didn't play the surfing game and sailed DDW exclusively.

sc52s1.jpgcruz.jpg.4b23cfba53474bc68826a863867daa8d.jpg

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On 6/11/2021 at 3:20 PM, Meat Wad said:

I've been told that my boat has a Zero Step Planing Hull. That little flat spot in the bow goes all the way back to the stern. And I swear I have planed at least once, the boat felt like it was on ice and not connected to the water at all.

Zap26_1600.thumb.jpg.37028e47aff9b2867fdd5adc270dd9da.jpg

 

As for the submarining discussion. Here is the greatest shot of them all. Can you imagine the load on the backstay?

merlin_submarine.jpg.767acd051bc27d256afb3fbb52c28085.jpg

Possibly a load in their trousers too

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2 hours ago, unShirley said:

 

Back in the 60s I was a kid sailing an FJ, or on a Kite, 420, 505, etc.  So, my comment (regarding agreeing that planing was determined by the stern wake moving away from the transom) was relative to planing dinghys.  Now that I am in my golden years, I have reverted to my dinghy days, albeit with training wheels, by sailing a Weta.  The Weta main hull is like a skinny planing dinghy, so I still occasionally look down to see where the water is exiting the transom to determine if the main hull is planing or not.  Regardless of this discussion and the accuracy of my perception, it keeps me entertained.

Which is the whole point.  

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On 6/13/2021 at 12:55 AM, Grrr... said:

And you remain on the face of the wave.  With big enough waves, you can surf down until you hit the wave face, but you aren't gonna go faster in the same direction as the wave than the wave speed.  You're being a little pedantic when you start arguing relative directions.

Not at all. And whether a boat is planing is all relative - it is the boat speed relative to the water, not anything else. So if that water is moving, sure, it is a factor when talking about speed, but not the only one. Are you really going to argue that a boat or a surfer riding along the face of a wave at 25 knots, is not going faster than a wave traveling at 8 knots?

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On 6/10/2021 at 1:42 PM, fastyacht said:

A 3o foot sailboat can and will sirf the wake of a 45 footers. Even old tymie boats

I think what you are referring to there is what used to be called "getting a tow" back in the IOR Days.

A smaller boat, if they positioned themselves right as a larger boat passed by downwind could match the speed of the larger boat through wave cancellation.

You'd position your boat so the trough of your boats wave system coincided with the crest of the larger boats stern wave.  We did it at least a couple of times on a Peterson 1 Ton (27.5 rater) where we locked onto 2 Tonners.  Unfortunately, due to the size difference we couldn't do it for too long - maybe a half mile or so

But if the boats are fairly similar in size say a post 1983 1 Ton (30.5 rater) and a 2 Ton, the 1 Ton could get towed indefinitely.

Although I recall reading about a 1 Ton getting a tow off a 2 Ton then deciding the 2 Ton was actually holding them up, so they heated up and and blew by in fairly short order.  Might have been a lighter weight French 1 Ton.  I think it was either a Briand, Fauroux, or Andrieu design.  Can't recall exactly -  one of those anyway.

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On 6/13/2021 at 3:48 AM, TwoLegged said:

So how did they explain the 1951-built Huff?  Was that also somehow not-planing?

https://www.nationalhistoricships.org.uk/page/shipshape/huff-arklow-restoration

Commonly held notions are reinforced by peoples' own experiences.  They don't have to account for anything they've not seen. And you're talking about an era when Disp/Length ratios were routinely above 300.

Cornelius Shields, considered one of the best racers of his day, wrote that hull speed was an absolute limit, that a boat sailing DDW in a good breeze would not accelerate in a puff, but that an aggressively sailed boat could gain a little in the lulls. No one believes that anymore.

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That makes sense, @SemiSalt  People are often unable to distinguish between the proposition that "X is not possible with the equipment I know" and the broader proposition that "X is never possible".

Similar problems apply in social policy, where many people assume that social structures which work for them (or their acquaintance circle) will work for everybody, or conversely that something they don't want in their lives is bad for all human lives.

It's odd, tho that Shields was either unaware of the Flying Fifteen (a 1948 design), a planing keelboat ... or somehow persuaded himself that no later design made of unobtanium could achieve similar performance from a bigger boat.  Or was this pronouncement pre-1948?

My instinct is to see this another example of the deep conservatism of the US East Coast Yachting establishment.

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On 6/12/2021 at 10:30 PM, Crash said:

This is really a discussion about drag.  A displacement boat surfing down a wave is still experiencing a significant amount of drag.  That's why so much water is being moved (large bow wave).  The boat may be going 14 knots, but it is still in a high drag region, and in a displacement mode.

A planning boat has seen a reduction in drag (due to a change in hydrodynamic lift vs drag) which allows the boat to accelerate given the same amount of power.  

My Boston Whaler 110 Sport is a great example.  With three people on board, sitting in the normal seats/positions, the 25 hp outboard can not push the boat on to a plane and accelerate beyond about 10 knots.  It's stuck in a displacement mode, pulling a huge stern wave even at full power for an extended period of time.  Move a person forward to sit up on the bow, and you change the trim (and angle of attack of the hull) and the boat will accelerate up on onto a plane with no increase in the amount of thrust the engine is providing (yes, the thrust angle does change some which helps, but no amount of engine trim will get the boat onto plane without weight distribution change).

Planning occurs when hydrodynamic lift results in a reduction of drag, and allows the boat to accelerate well beyond hull speed with no increase in the thrust the engine (sails) is/are providing

I guess you wouldn't consider the Inland Lake Scows to be planing boats then.

A-ScowDragCurves.thumb.jpg.940fb845c95b032be846d0fbd9e426c5.jpg

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21 minutes ago, Doug Halsey said:

I guess you wouldn't consider the Inland Lake Scows to be planing boats then.

A-ScowDragCurves.thumb.jpg.940fb845c95b032be846d0fbd9e426c5.jpg

That looks  plany to me. Friction goes with square of speed. This plot is staight on linear grid...that means residuary resistance decreasing along with surface area, driving down the overall resistance to linear.

Who gathered this data and when? Looks suspiciously Marchajian.

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19 minutes ago, fastyacht said:

That looks  plany to me. Friction goes with square of speed. This plot is staight on linear grid...that means residuary resistance decreasing along with surface area, driving down the overall resistance to linear.

Who gathered this data and when? Looks suspiciously Marchajian.

It looks "plany" to me too. My intention was to counter Crash's implication that planing necessarily causes a reduction in drag as the speed increases. 

Yes, the chart was taken from Marchaj's Sailing Theory and Practice, but I couldn't tell from the text where the data originated.

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1 hour ago, Doug Halsey said:

It looks "plany" to me too. My intention was to counter Crash's implication that planing necessarily causes a reduction in drag as the speed increases. 

Yes, the chart was taken from Marchaj's Sailing Theory and Practice, but I couldn't tell from the text where the data originated.

I can't find the post by Crash where he states that.  The closest I can find is the post by Borracho below where he states wave making drag is reduced when planing.  I'm not sure about that contention although it may well be true.

But I do know that overall drag never goes down when planing.  if it were the case, a boat could be caught in a "Twilight Zone" where it would never come off plane as it would caught in a hollow of the drag curve and it would take more power to push it up the backside of the curve to slow it down. 

A simple example is a power boat.  Once it is on plane it always takes more power to generate more speed and if the driver backs off on the throttle, the boat will slow down.  If drag were reduced, that would not be the case - the speed would either increase or remain the same

Now the Drag Coefficent curve can have hollows, but drag is always increasing as speed increases.

On 6/10/2021 at 3:48 PM, Borracho said:

Well...hull speed is definitely a real thing, @fastyacht.. It is defined as the speed at which the wavelength of a boat's bow wave equals the waterline length of the vessel. The value  does not vary except with waterline length except for a tiny amount due to water salinity and. The incremental amount of energy to increase the vessel speed beyond the hull speed varies with the characteristics of the boat. However in engineering, it is now (for 200 years?) replaced by the more scientific Froude Number.

Planing is defined as the mode where hydrodynamic lift overtakes buoyancy (hydrostatic lift). Surfing is being propelled by a steep or breaking wave without regard to planing. Surfboards are always planing while surfing. Waves in the open ocean are unable to accelerate a floating object unless somehow steepened. A floating ball will not roll down the face of even a huge ocean swell, for example. Nor do boats change speed in such seas. Steepening can be from entering shallower water or from being driven by wind. Heavy slow boats entering a channel with following seas often surf for a moment, without planing, just before embarrassing themselves. In heavy following seas heavy displacement boats will surge somewhat beyond hull speed. Such boats tend to just create more wave drag until they either slow down or sink bcuz hydrodynamic lift never overcomes buoyancy. So the thread title Surfing vs. Planing is improper. Surfing and Planing would be better.

I don't think one can plane at less than hull speed. The water moves out of the way, around the hull, rather than producing any upwards force. 

As a boat begins planing the wave-making drag is reduced. For some boats the wave-making drag is already small so there is not much difference at the transition to planing. 

 

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9 minutes ago, 12 metre said:

Now the Drag Coefficent curve can have hollows, but drag is always increasing as speed increases.

Yes. I think the casual discussions above have confused absolute drag with the slope of the drag curve. The rate of increase in drag is reduced. A powered dinghy readily demonstrates that: Power can be slightly reduced and the dinghy continues to accelerate some but reducing power more returns the dinghy to displacement mode.

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