Author Topic: Width vs Length stability ratio?  (Read 8086 times)

Zich11

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Width vs Length stability ratio?
« on: May 27, 2016, 05:17:11 AM »
Recently took up the sport.  Have what is probably a stupid question.  If looking for a slightly more stable board is there any rough ratio between width and length when trying to get something a bit more stable.  For example,  does one inch wider accomplish same thing as 6 inches or one foot longer?  Sorry to bore you if it is a stupid question

Supshaper

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Re: Width vs Length stability ratio?
« Reply #1 on: May 27, 2016, 05:38:43 AM »
First, not a stupid question.  One I have and continue to be challenge with.   Just about every part of the board design plays into stability.   Length, width, template outline shape, volume, and experience being the primary factors.  King's website has a tool to help you calculate volume.
http://Http://www.kingspaddlesports.com/boardvolume/

I do not know that there is magic formula for this.   It is gong to depend on what kind of paddling you want to do and the conditions in which you will be paddling.  I suggest demoing a few boards to get an idea of what works for you.

Others will hopefully chime in here with good advice.  The last thing I will leave you with is the more time you spend on the water with any board the more stable you will become.  All of us wobbled in the beginning.    Good luck.

"Surfboards are in an infinite and endless evolution.  Just when the shaper thinks he has built the perfect board, he thinks of something different to make it better."  GL

TallDude

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Re: Width vs Length stability ratio?
« Reply #2 on: May 27, 2016, 07:53:10 AM »
There are so many factors that are a part of making a board feel more stable. Length is probably one of the lesser factors. Width is deceiving. You can have two boards the same width shape and length, but one will feel more tippy. Rail shape, bottom shape, rocker, and volume distribution all effect the stability. A board that has more rocker (nose to tail) will feel more stable than a flatter board. A board that has sharp bottom rails will feel more stable than a board with rounded bottom rails. A board with a flat bottom (side to side) will feel more stable than one with a rounded bottom. A board that has a flat deck (top side to side) will feel more stable than one that has a domed deck because with a domed deck there is less volume (buoyancy) near the edge of the board.
Shape affects the stability too. An all arounder (over sized long board) is the most common SUP shape. The shape wider nose to tail. It starts with a wide nose, gets wider, and ends with a wide tail. That is a very stable shape. With that shape you can go a little narrower and it with still feel stable. The all arounders are planing hulls with a flat bottom nose to tail. Not good for paddling distance because the bottom doesn't help it track, or go in a straight line. Race board or Touring boards have displacement hulls with point noses designed to part the water and travel in a straighter line. The longer the board, the straighter the line. The pointed nose is narrow, so the board will feel more tippy than an all arounder. Touring boards have more width and volume aimed towards distance paddling but more stability. Race board are designed to go fast at all cost. Rounded rails, narrower, reduced volume, and of course as light as possible.
There are more subtle design factors such as recessed foot wells to add stability with narrower boards. Fin shapes and sizes effect stability as well.

So pretty hard to find a ratio given these factors.
You can't define or prescribe a board and say that is the most stable board for you. It's what feels stable to you when you paddle it.  ;) 

Welcome to the zone.
« Last Edit: May 27, 2016, 07:58:06 AM by TallDude »
It's not overhead to me!
8'8" L-41 ST and a whole pile of boards I rarely use.

SlatchJim

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Re: Width vs Length stability ratio?
« Reply #3 on: May 27, 2016, 08:08:44 AM »
The smartass in me want's to say "6 of one, half dozen of the other" but I...ok I just did.

Imagine you're driving a corvette, low to the ground, hits corners at 1g with out blinking, super balanced, fast as hell.
Now imagine we're talking about the surface area that the corvette takes up, and you want to build a chassis that is both longer and wider. More stable right?

Well, the chassis  belongs to an 18 wheeler, with a 53 foot trailer, double stacked with pallets of sheet metal screws overweight by 20,000 pounds and any slight variation in side to side elevation makes you feel like you're about to slide off a cliff.

A boogie board is stable as hell as long as you're laying on it.  Bring the center of gravity up at your own risk.  As Suppers, we have to add to the equation things like age, health and balance issues, water chop and turbulence.  Each different rider will have their own perfect stability equation  Mine has gotten better over time but because of my size and age, I can't even look at boards that pros surf. 

If there's a lesson to all this babbling, it's that a demo ride on a board is the only fool proof way to know.  It matches the load to the vehicle without any speculation.  I have been accurate on some and completely off target on other boards when picking out what works for me.

mrbig

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Re: Width vs Length stability ratio?
« Reply #4 on: May 27, 2016, 08:21:40 AM »
As a guy who had years of surfing experience and lousy balance when standing still I learned that width was more important than length or liters all things being equal. And they never are!

Beg, borrow, demo, steal and find out what works for you and your unique skills, experiences et cetera et cetera!
Let it come to you..
SMIK 9'2" Hipster Mini Mal
SMIK 8'8" Short Mac Freo Rainbow Bridge
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supsurf-tw

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Re: Width vs Length stability ratio?
« Reply #5 on: May 27, 2016, 08:37:58 AM »
It's a balancing act (literally) between many factors. 2 of the biggest factors are nose and tail width. A narrow nose and\or tail on a wide board is much less stable than a shorter board with a wider nose\tail. Also remember that thicker doesn't necessarily mean more stable. Go from there....
Boards:

 
8-10 x 31 Egg
8-11 X 32 Double wing Fangtail Tom Whitaker
8-6 X 30 1\2  Inbetweener Tom Whitaker
8-4 x 30 Hyper quad Tom Whitaker (wife's now)
8-4 X 31 1\4.  Round (wide) Diamond Tail Quad Tom Whitaker
 9-4 X 30 1\2. Swallow Stinger Quad Tom Whitaker (ex wifes now)
10-0 Brusurf for teach

anonsurfer

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Re: Width vs Length stability ratio?
« Reply #6 on: May 27, 2016, 08:52:04 AM »
If looking for a slightly more stable board is there any rough ratio between width and length when trying to get something a bit more stable.  For example,  does one inch wider accomplish same thing as 6 inches or one foot longer?  Sorry to bore you if it is a stupid question

For stand up surfing boards I have owned: 3L = +3" in length = +1" width = 1/8" thickness (assumes similar shape and foil).

So a 7-10 x 27 will have the same approx volume as a 7-7 x 28. 

For me width helps stability more than length.   If you like your current boards volume but want more stability, go 2-3" shorter and 1" wider.  If you want more volume AND stability keep the length the same and go 1" wider.

Home Break: Doheny
Tic Tac v3 (Hoglet): 6' 6" x 23" x 3.6" x 67L
Omni: 6' 9" x 23" x 3.75" x 68L
Tic Tac (OG): 7' 0" x 22.75" x 3.5" x 70L
In The Pink (Incoming): 8' 0" x 22.9" x 3.25" x 70L

Blackproject Surge S77 (Soft Flex Shaft, T-Grip, +0" OH)

Zich11

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Re: Width vs Length stability ratio?
« Reply #7 on: May 27, 2016, 09:25:42 AM »
Thanks everyone. Appreciate the insight.  Have a good weekend

PonoBill

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Re: Width vs Length stability ratio?
« Reply #8 on: May 27, 2016, 09:56:51 AM »
Initial stability of a hull comes from righting force (technically, the righting moment), which means the force that resists tipping. When a board is flat in the water the center of gravity and the center of bouancy are aligned vertically at the waterline. Center of gravity is the effective location of all the force pushing down, center of bouyancy is all the force pushing up. Excess bouyancy contributes nothing to initial stability since the amount of force pushing up equals the amount of force pushing down (unless the board is underwater). When the board first starts tipping, the center of bouyancy shifts toward the rail. The further the center of bouyancy shifts, the more righting force is applied. The wider the board is, the longer the righting arm can be, but the righting arm is only as long as the tipping force makes it. A longer board exerts more upward force for any amount railward shift of the center of bouyancy (tilt), because there is more volume being submerged, but greater width means the righting arm can be longer so the leverage is greater. But remember that the amount of righting force applied upwards only equals the tipping force (statically). A narrow board can be as stable as a wide board until the limit of righting arm length is reached.

We could produce stability curves for any specific board, but it would be a bit meaningless because the initial stability of a surfboard is kind of meaningless compared to what's going on up top. We have a twenty pound hull carrying a 200 pound person with the center of gravity of that loosely coupled weight being a couple of feet above the board. If that weight with that high center of gravity were statically attached to a surfboard it would be upside down very quickly. So all the other factors people have talked about which affect the board dynamically are at least as important as the width and length.

I don't know if that really clarified anything, but it made me feel better to get that out of my head.
« Last Edit: May 27, 2016, 10:04:21 AM 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.

SlatchJim

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Re: Width vs Length stability ratio?
« Reply #9 on: May 27, 2016, 10:39:42 AM »
Oh sure, bring SCIENCE into it.  ;)

starman

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Re: Width vs Length stability ratio?
« Reply #10 on: May 27, 2016, 10:55:28 AM »
My basic rule of thumb is greater width equals greater stability and greater length equals better glide. One just needs to find their comfort zone when it comes to balance. Then find the board with the best width and length for you own enjoyment.

Dusk Patrol

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Re: Width vs Length stability ratio?
« Reply #11 on: May 27, 2016, 12:34:59 PM »
Are you sorry you asked?  ;D 

The good news is that you'll learn a lot from the "first" board you're contemplating now, and probably soon be in the market for another that suits your advancing experience and skill levels. So whichever you get, consider resale value!   
RS 14x26; JL Destroyers 9'8 & 8'10; BluePlanet 9'4; JL Super Frank 8'6

PonoBill

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Re: Width vs Length stability ratio?
« Reply #12 on: May 27, 2016, 04:50:42 PM »
Okay, I cleaned my shop some and had a beer as well as a couple of Landjaeger, and I remember what point I was trying to make. Long boards sometimes feel very stable initially, because a comparable board that is just wider doesn't add a lot more stability until the center of buoyancy for the narrower board reaches the rail. If your balancing reactions are quick and the center of bouyancy never approaches the rail, you won't find a big difference in stability.

That's it. ta da. Back to your regularly scheduled broadcast.
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.

Zich11

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Re: Width vs Length stability ratio?
« Reply #13 on: May 28, 2016, 05:22:16 AM »
PonoBill...your in depth explanation of the physics of a board was terrific...should be required reading for all us new guys    thanks again, everyone

jd

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Re: Width vs Length stability ratio?
« Reply #14 on: May 28, 2016, 10:28:12 AM »
Lots of board characteristics affect stability besides length and width.  Shorter length affects stability by cutting down the "sweet spot" so to speak where you can balance.  Case in point.  I have a 9'6" x 31 JP Surf and an 8'5" Sup Sports Hammer that is 31.5" wide I think.  Both about the same volume JP is 146 and the Hammer is 141or 5.  Stability of the two boards is not even in the same ball park. 

The JP is hands down far more stable; like a barge compared to the Hammer and surfs about 1000 times better.  The Hammer also has a wider nose and tail by a long shot.  The Hammer has the most bulbous rails I have seen on a board and probably contributes to its inability to right it self once you sink a rail.  The water just holds all that rail and doesn't want to let it back up.  The Hammer at over 31" wide is probably the most unstable board I've ridden.  10' C4 and Jimmy Lewis boards I had that were 28" wide were much more stable than the Hammer.  Proper design in all the parts plays a big part.

I also had a 17' Naish that was 26" wide.  The rails were almost vertical in the middle of the board and it had a narrow nose and tail.  Super stable in the worst of ocean conditions.  Normally at my height and weight 6'4" 230, 28" is about the minimum width I want on a board.  The Naish would only tip over so far and not enough to ever go past the point of no return. 

 


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