Author Topic: Primary Stability vs. Secondary Stability  (Read 8113 times)

Ichabod Spoonbill

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Primary Stability vs. Secondary Stability
« on: May 15, 2014, 02:37:10 AM »
I've been hearing the terms primary stability and secondary stability bandied about for some time, and I confess I don't completely understand them. What I'm guessing is that the primary stability of a board is it's ability not to tip over. Secondary stability come in play after the board is tipping, and it's whether the board tips over or not.

Could anyone clarify this for me?
Pau Hana 11' Big EZ Ricochet (Beluga)

feet

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Re: Primary Stability vs. Secondary Stability
« Reply #1 on: May 15, 2014, 03:08:21 AM »
My understanding of these terms comes from the sea kayak world.

Primary stability is the sense one would feel as they sit/stand motionless on the water. Something that is wide and flat would have high primary stability.  In the kayak world, the hull design for primary stability was aimed at recreation paddlers in shorter (10-12 ft), wider (29"+) kayaks. 

Secondary stability is the sense one would feel as they pushed one side of the craft towards the water, either to initiate a turn or because of rough sea conditions.  Typically, a craft with good secondary stability would be longer (16-17 ft) and skinnier (21-23" wide) with a hull design that actually increased the amount of craft in the water as it tipped to a side, which gives the sense of greater stability. 

See this link for some technical explanation:

 http://www.guillemot-kayaks.com/guillemot/information/kayak_design/kayak_stability

And here is an explanation from paddling.net as it refers to canoe design: http://www.paddling.net/guidelines/showArticle.html?86

Canoe Hull Shape Defined
After the raw dimensions of length, width and depth, canoe performance is determined by hull shape. Front, side and overhead views of the boat give you cross-section, rocker, hull symmetry and taper.

Cross-section-Initial and Secondary Stability

The cross-sectional shape of the bottom and sides of the canoe will influence its performance, especially its stability. Stability is divided into initial (primary) and final (secondary). Initial stability is what you feel when you first get into the boat. In a boat with great initial stability, you can stand up and walk around. It takes a lot of effort to flip this boat on flatwater. It resists leaning until it reaches a point of no return, beyond which it quickly upsets without much warning. That's because secondary stability was sacrificed for the stable platform of initial stability. Secondary stability refers to how the boat behaves as it tilts. A boat with great secondary stability may feel tippy at first-it's easy to lean onto its side. But it feels stable and predictable in the lean. This is a useful characteristic for whitewater moves and rough-water paddling.

Flat-bottomed canoes offer great initial stability at the expense of speed and rough-water performance. Very secure on calm water, they're great for sportsmen and recreational paddlers. Round-bottomed boats are the other end of the spectrum. Perfectly rounded bottoms allow for clean entry and exit lines and minimal surface area in the water. They have great speed and efficiency but virtually no initial stability. This is why racing rowing shells are round-bottomed but canoes, except for a few fast, specialized designs, usually are not. Most canoe designs are a compromise between flat and round, with shallow-arch or shallow-V bottoms. These designs sacrifice varying degrees of initial stability for good secondary stability and all-around performance. The cross-section of some canoes is modified by the addition of a keel. A keel is a moulded ridge or attached piece of material that runs the length of the canoe on the bottom outside of the boat to help the canoe track and resist the influence of crosswinds. Keels are most often found on short, wide canoes used for recreation and sporting. They are undesirable in whitewater because they reduce manoeuvrability and are vulnerable to rocks.

The sides of the canoe are either flared, turned-in or straight. Flared sides shed water. Tumblehome describes the shape of a canoe with turned-in sides. Tumblehome results in a narrower beam at the gunwales making it easier for the paddler to reach over the side of the canoe when paddling. Straight-sided canoes are a balance between the paddling efficiency of tumblehome and the dryness of flare. Canoe designs will incorporate one, two, or all three of these in different areas of the hull.

XLR8

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Re: Primary Stability vs. Secondary Stability
« Reply #2 on: May 15, 2014, 05:05:40 AM »
Initial stability vs. secondary stability and the importance of finding the balance between....good question and good response from feet.  This is an important concept and I tend to focus more on secondary stability than initial.  If a paddler can be tolerant of the "tippy" feeling experienced initially, in a well-designed hull you can find near rock solid secondary stability.  Learn to ride that by adding momentum to create more stability, add in some foot steering and subtle weight shifting to increase handling, angle into cross swell or at least drop a rail slightly and suddenly some of those crazy tippy boards are real fun to ride!
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spookini

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Re: Primary Stability vs. Secondary Stability
« Reply #3 on: May 15, 2014, 05:16:38 AM »
Primary stability:  used to describe a board you have owned for several seasons, but have become tired of.  You yearn for something... sexier.

Secondary stability:  used to sugarcoat the fact that you can't stand on the sexy new raceboard you just paid $xxxx.xx for.  Often muttered while wearing rose-colored (sun)glasses.

Used in a sentence...  "Umm, it's not quite as 'user-friendly' as my old board, but I'm sure once I get the secondary stability 'dialed-in', it's gonna be awesome." 

 :o ;D
« Last Edit: May 15, 2014, 05:19:39 AM by spookini »
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stoneaxe

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Re: Primary Stability vs. Secondary Stability
« Reply #4 on: May 15, 2014, 05:49:00 AM »
Secondary stability=fall in slower....at least for me..... ;)
Bob

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Wetstuff

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Re: Primary Stability vs. Secondary Stability
« Reply #5 on: May 15, 2014, 07:05:36 AM »
Icky, ..for me,  Primary stability is the amplitude and duration of the 'Wiggles' ... Secondary: as Stoney said. 

A day ago I found a staggered stance (about 20% overlap) on my 12-6 decreased stability but hopefully increases my ability (over the long run) to handle it.

Thanks for posting that Feet. I am not smart enough to absorb it all but I appreciate reading it.

Jim
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PonoBill

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Re: Primary Stability vs. Secondary Stability
« Reply #6 on: May 15, 2014, 07:47:20 AM »
Primary stability is really a term of convenience. But for simplicity of explanation let's pretend it actually exists. Consider a trimaran with both amas firmly in the water. if you shift your weight, nothing much happens because the boat has a lot of primary stability. Now change the ama setup so both are out of the water. When you shift your weight the boat tips until the ama touches, and then becomes stable--secondary stability.

For a surfboard, secondary stability is derived from the plan shape (width, etc,) rocker and the rail shape. If the center of the curve of the rail is above the waterline, as you tip the board the distance from the center-line of the board to the waterline on the rail gets wider because water is moving up the curve. That gives some secondary stability--resistance to further tipping. The rocker of a board acts like a weight in a hammock. Any lateral movement has to raise the weight on the board, so there is some secondary stability added. There's also changes in what parts of the hull are submerged depending on how much of the nose and tail are out of the water, and what their shape is. A square tailed board with tail rocker adds secondary stability because the section of the tail that's above water starts to submerge as the board is tipped, adding buoyancy to that side.

Really, all the stability of a surfboard is "secondary" because the stability comes from dynamic changes to what parts of the board are submerged and how much weight must be lifted for the board to rock. Primary or initial stability is just what happens early in the tipping, and secondary is what happens later. The board has to tip a little for buoyancy distribution to change and impart a righting force. At least that's what Mr. Newton says.
« Last Edit: May 15, 2014, 07:49:30 AM by PonoBill »
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Subber

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Re: Primary Stability vs. Secondary Stability
« Reply #7 on: May 15, 2014, 08:58:51 AM »
To me,

"Primary stability" is the speed or amount of initial tipping.

"Secondary stability" is the speed or amount of tipping after the initial tipping.

My surf sup has poor primary stability....it feels tippy,
but after it tips many inches, then secondary stability kicks in,
and, if you realize/have confidence that the secondary stability is going to hold,
you can bring it back without falling.  That combo makes it surf well,
you can bury the rail and do a nice bottom turn, etc. and keep riding it.

I was on a custom home made kayack once that had essentially no secondary stability.
So intitially it tipped slowly...but at a point, you just flipped completely over -
no secondary stability - the opposite of a good design & LOL and why my friend
was able to buy it for $40!
Jimmy Lewis Black & Blue Noserider 10'1"x31"x4.25," 164 liters, 24 lbs, 1 box
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Takayama Ali'i II Surftech 11'x21.375”x28.5”x17.25”x 4.25,” 162 liters, 26 lbs, 3 boxes

Ichabod Spoonbill

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Re: Primary Stability vs. Secondary Stability
« Reply #8 on: May 15, 2014, 10:11:37 AM »
Thank you, everybody for your answers, especially Feet. I learned a lot. Now I want to go test the secondary stability of every board I own!
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southwesterly

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Re: Primary Stability vs. Secondary Stability
« Reply #9 on: May 15, 2014, 12:51:41 PM »
There is no secondary stability if you have a board that you continually fall off of.

pdxmike

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Re: Primary Stability vs. Secondary Stability
« Reply #10 on: May 15, 2014, 01:26:30 PM »
You can simulate the difference somewhat by standing on a board with your feet wide, then with them narrow.


When they're wide, you feel very stable, but if you put weight on one foot (on purpose, or due to some chop hitting the board) the board will tip dramatically.


When they're narrow, you don't feel very stable, but if you put weight on one foot, it won't make much difference.


Someone's probably said this, but it seems like for a lot of boards, the better the primary stability, the worse the secondary, and vice versa.  (That's what happens with the foot example, too.) 




pdxmike

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Re: Primary Stability vs. Secondary Stability
« Reply #11 on: May 15, 2014, 01:28:17 PM »
Also, an extreme board design will have either primarily secondary stability and secondarily primary stability, or it will have primarily primary stability and secondarily secondary stability.  A more balanced design will have neither primarily or secondarily primary or secondary stability. 

sup_surf_giant

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Re: Primary Stability vs. Secondary Stability
« Reply #12 on: May 20, 2014, 09:48:47 PM »
As Pono said, stability is a rapidly changing thing.

Give me a fat but athletic dude and he can ride loads less volume than a skinny guy with little athleticism.

Give me a quick learning and sharp thinker, and with a little instruction they can get about on an "unstable" board rather quickly.

But conditions, tide, wind, backwash, currents all impact stability be that primary secondary or tertiary. Ummm what?
Taller than most, shorter than others.

TallDude

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Re: Primary Stability vs. Secondary Stability
« Reply #13 on: May 20, 2014, 10:11:10 PM »
To keep it simple like me, an average board with thick rails (any shape) will be initially stable and stable when put on edge. As Pono said, lots of buoyancy allows you time to recover your balance. A board with thin rails may initially feel stable, but not so when put on edge. The lack of buoyancy at the rail makes it hard to recover your balance.
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