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Date: Fri, 09 Apr 1999 23:02:27 -0700
From: Ralph Diaz
Subject: Re: [Paddlewise] stability of folding vs. hardshells

Leander wrote:
> 
> At 11:44 AM 09-04-99 -0700, Philip Torrens wrote:
> >
> >Okay, I can't express this in formal technical terms, but I think Ralph
> may be right (upright?) in feeling that a sponsoned folding boat could be more
> stable and self-righting than a hardshell of equal chine and beam. (I mostly use
> hard shells so I'm not biased in favour of folding boats.)
> The displacement of a hardshell is essentially static, changing only as the
> entire boat moves. The sponsons of a folder, in contrast, are squeezed at the
> bottom as they are pushed deeper into the water, and therefore expand into
> greater width and stability in the higher parts.  ...snipped...
> 
> I long ago read an article on this very subject, complete with formulas,
> but it basically said what you so eloquently and succinctly described. Though the
> reference is long since lost, perhaps the design experts on the list, such as
> John or Nick, know of it.

Philip's and Leander's comments remind me of something interesting about
the way a sponsoned folding kayak behaves when it has taken on a lot of
water.  If you turn that folding kayak on its side, it will rise on the
sponson on that side and spill a lot of the water out, up to about the
inside level of the sponson.  (It is a neat way to begin partial
emptying of a folding kayak that most people don't know about.  The
phenomenon is even more pronounced if you also have flotation bags fore
and aft as you alway should in any folding kayak or non-bulheaded
kayak.)

If there were no different in the displacement effect between a
hardshell and a folding kayak with sponsons, then this float-up
phenomenon would also happen with a hardshell laid on its side.  To my
knowledge, the hardshell would not at all rise that way to spill out the
water, only the sponsoned kayak would.  That column of compressed air in
the sponson is fighting its way to the surface.  In a corollary way, it
also resists being submerged.  Philip's idea of a dynamic as opposed to
static displacement certainly has a ring to it that shows itself in real
life.

There are so many ways of skinning a cat in the kayaking world.  Some
corners of this realm offer some unique advantages that some people
don't seem to want to hear about or want to put outside the kingdom's
gate as not worthy.  For example, the earlier sit-on-top kayak
discussion that I engendered that drew some flak.   But let's face it,
there ain't nothing easier to empty than an SOT nor much easier to get
back into without pumps, paddle floats, re-enter and roll and all that. 
Also the middle range of SOTs are every bit as fast as the middle range
of beamier hardshells made of polyethylene and are considerably stable. 
Performance kayaks require performance paddlers and a lot of people
getting into kayaking are simply not going to work at getting and
keeping the skills.  Wouldn't these paddlers be better off with kayaks
that are less skill reliant?

ralph diaz  
-- 



Date: Sat, 10 Apr 1999 01:29:38 -0700
From: Dave Kruger
Subject: Re: [Paddlewise] stability of folding vs. hardshells

Ralph, this is completely accurate to this point.  The [emphasized] part of
your next sentence (see below) describes an effect which is not physically
possible until the inflated tube is **completely** submerged, thereby
displacing a volume of water equal to the sponson's volume, giving a
buoyant effect equal to the weight of the water displaced.  Any restoring
force, as Philip points out, which acts to right the kayak,  *before*  the
sponson is *completely* surrounded with water (both inside and outside the
yak), is due to the *form* of the outside of the yak, and can not be
affected by what is inside the yak.  OTOH, I think Philip may have
correctly identified the source of the "feeling" you and he describe -- it
is due to local deformation of the *outside* of the yak's surface, owing to
the flexible character of the hull.

> In a corollary way, **it also resists being submerged.** [emphasis added]
> Philip's idea of a dynamic as opposed to static displacement certainly has
> a ring to it that shows itself in real life.

Yes.  The *dynamic effect* could be genuine.  The "resists being submerged"
can not. I love my folding boat, but it can not violate principles of
physics or buoyancy.

-- 
Dave Kruger
Astoria, OR




Date: Mon, 12 Apr 1999 08:37:34 -0700
From: [Ralph Diaz]
Subject: Re: [Paddlewise] Group Paddling - folders stability

John Winters wrote:

>> Which bring me to something, John, that you said in your early posting,
>> "Many paddlers achieve this result by packing their boats with waterproof
>> bags along the interior sides of their rigid boats."  I have never seen
>> anyone do that in a hardshell.
> 
> Perhaps this has to do with ignorance. I do this on my boats when I do not
> have a sea sock or pod. I use a multitude of small gear bags. Some boats,
> may lack enough beam for this kind of thing but foam sheathing glued to the
> hull sides to reduce volume also works. Reducing the floodable volume in
> the boat ios the objective. I doubt if most paddlers understand or consider
> the effects of free surface in their boats.  Most production boats don't
> come with methods to attach side bags, sea socks, or pods and that seems to
> me a serious omission.
 
> I cannot say why builders of hardshells fail to recognize the importance of
> flooded stability. As Ralph points out, all they need do is look at folders
> to see them in use and apply the same principle.

Well, as I pointed out, Bavaria does or did that (I haven't seen their
kayaks in awhile).  All it takes is to glass in some nylon twine or
webbing straps every 2 feet or so along the sides inside the kayak. 
Sponsons than can be added for that desired effect. I found very
interesting your comments the relative instability of bouyancy located
at the ends of the boat and the free surface inside the cockpit. 

> 
> Please don't call internal buoyancy bags sponsons. Sponsons attach to the
> outside of the boat. Buoyancy bags and tanks attach inside.

I would love to and Webster's dictionary (and I am sure all naval
architecture glossaries of terms do too) but sometimes things get called
something and the label sticks and we just have to start using the term
in the corrupted way.  :-) 
But I do appreciate that there is a distinction...anything to get away
from the infamy the term has gotten because of your fellow Canadian.

I want to return to the question of stability of buoyancy aids in
folding kayaks.  And then I am going to leave it because no one seems to
be applying any real science here other than general, unspecified
references to Archimedes.  What I have to say comes from observation,
which has to count for something.

Many years ago, long before the idea of doing anything with folding
kayaks ever even entered my mind, I observed what happened with folding
kayaks in two situations that I can only attribute to something to do
with the buoyancy aids inside their soft skins.  In the first one, I was
on a group paddling trip.  I was directly alongside a couple in a double
Klepper, when the fellow decided to stand up (he later said he wanted to
stretch his legs).  He wasn't very well coordinated and he tipped the
kayak over.  I was about 30 feet directly to the side of his Klepper and
all I saw was black bottom and keel strips including the ones on both
chines, i.e. the kayak was almost completely on its side.  He fell out
and the kayak righted itself.  The woman in the front had only paddled
once before and hadn't the faintest idea of what a bracing stroke
was...so it wasn't she that righted the kayak.  The kayak wound up right
side up with the woman having a stunned look on her face.  I am not sure
how another kayak, a non-buoyancy aided flexible skin one, would behave
in similar circumstances.

Another observation, again from my pre-evangelistic folding kayak days. 
I was paddling a double Klepper with my wife in our first months of
kayaking experience.  We went out through surf off of Brighton Beach in
NYC.  I was fiddling with a rudder lifter that I had added to the kayak
(they lacked them then and it was the first thing that I ever innovated
for the kayak that eventually got me interested in writing about this
particular species of kayaks) and did not pay heed to what was happening
with the waves coming in on us.  The kayak completely broached, so much
so that our kayaking friends on the beach with many years of kayaking
and kayaking teaching experience fully expected our Klepper to
windowshade all the way back to the beach.  It didn't.  While the wave
side of the kayak rose way up and we were well over, something kicked
in, without any bracing whatsoever by either of us...my wife didn't know
how to brace and both my hands were on my rudder lifter line.

Will folding kayaks flip?  Of course they can and do.  But it takes a
lot, and my observation tells me that the bouyancy aids inside are
kicking in at some point to some degree enough to say that the
phenomenon does exist.

ralph diaz 
-- 





Date: Tue, 12 Sep 2000 08:47:57 -0700
From: Kevin Whilden
Subject: [Paddlewise] Instability of folding kayaks (was Re: Rolling a
  K-lite)

At 07:21 AM 9/12/00 -0700, ralph diaz wrote:

> But the issue of rolling a folding kayak is almost academic.  They are
> not prone to tip and even a modicum of a brace will keep you upright in
> absolutely insane waters, or just working like the devil to stay
> centered in your boat will do.



> Most folding kayaks have a low brace built into them.  They all can tip
> but they have to go pretty far over to do so.

Ralph, I think there is line between when folding kayaks are more stable or 
less stable than narrow hardshell boats, which I would like to define a 
little better and eliminate confusion.

I am skeptical that folding kayaks are so stable in waters that some people 
on this list would call "absolutely insane". This is definitely a relative 
term, is it not? Never having paddled a folding kayak in rough seas, I 
cannot say for sure, but I have always thought that too much primary 
stability increases the chance of capsize in big steep waves or really 
nasty (by my metric) tide rips.  For example, has anyone paddled a wide 
folding kayak in the tide rip behind the surf wave at Skookumchuck? Now 
that is what I call "insane waters"  -- I have never seen a more confused 
mixture of  2-3 foot high boils with an occasional deep violent whirlpool. 
Even the hardcore whitewater crazies avoid that place, and choose to float 
down a 1/4 mile (in rodeo boats) before trying to cross that eddy fence. 
But if one were to find themselves in an eddy fence of that magnitude, I 
would rather be in a narrow "tippy" boat with great secondary stability 
than in wide "stable" boat with high primary stability. Then I would be 
more able to react with an insta-brace.

In a less extreme example, such as steep wind waves, high primary stability 
tends to make the boat lie flat relative to the local water's surface. But 
if that surface is nearly vertical (as in a steep wave), then a capsize is 
imminent unless the paddler attempts an ill-advised down-wave brace (a 
danger for shoulder dislocations). A low primary, high secondary stability 
boat can just edge into the steep wave ever so slightly, ride over it, and 
have no fear of capsize. Again, since I have never paddled a folding kayak 
in rough water, at what point does the high initial stability become a 
drawback in terms of remaining upright?

Thanks,
Kevin

Kevin Whilden



Date: Tue, 12 Sep 2000 12:24:29 -0700
From: ralph diaz
Subject: Re: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)

Kevin Whilden wrote:
>
> 
> Ralph, I think there is line between when folding kayaks are more stable or
> less stable than narrow hardshell boats, which I would like to define a
> little better and eliminate confusion.
> 
> I am skeptical that folding kayaks are so stable in waters that some people
> on this list would call "absolutely insane". This is definitely a relative
> term, is it not?

I really don't know an absolutely definitive answer to your question. 
Folding kayaks have been in far hairer waters than I would ever want to
be and have done fine.  Examples: In 1990, a fellow Joe Weight took a
double from Grenada to Puerto Rico and got caught in a hurricane in
about a 60 mile crossing toward the end and didn't capsize.  The
hurricane was insane enough but he regularly was in pretty insane
stuff.  Two guys took a double folding kayak from Sydney to Darwin some
3,000 plus miles along the rugged surf eastern shoreline of Australia. 
They capsized, I believe just once in some 100 days of paddling.  Some
of the waters they were in were absolutely insane by any definition.  A
lot of the staying upright for these guys and hundreds of other
expeditioners was due as much to the stability of the boats as the skill
of the paddlers.


> Never having paddled a folding kayak in rough seas, I
> cannot say for sure, but I have always thought that too much primary
> stability increases the chance of capsize in big steep waves or really
> nasty (by my metric) tide rips.  For example, has anyone paddled a wide
> folding kayak in the tide rip behind the surf wave at Skookumchuck? Now
> that is what I call "insane waters"  -- I have never seen a more confused
> mixture of  2-3 foot high boils with an occasional deep violent whirlpool.
> Even the hardcore whitewater crazies avoid that place, and choose to float
> down a 1/4 mile (in rodeo boats) before trying to cross that eddy fence.

Sounds ominous.  I would not want to be in that stuff ever.  Who would?

> But if one were to find themselves in an eddy fence of that magnitude, I
> would rather be in a narrow "tippy" boat with great secondary stability
> than in wide "stable" boat with high primary stability. Then I would be
> more able to react with an insta-brace.

Greater secondary stability is only as useful as the paddler's ability
to brace and use it constantly for long stretches of time.  Again, it
does sound like a challenging spot for any boat.  I have no way of
knowing how well a foldidng kayak would fair.  I doubt that most
kayakers in skinny tippy boats would do well either.  It sounds like a
place for our good friend, Superman Doug of BC!

> 
> In a less extreme example, such as steep wind waves, high primary stability
> tends to make the boat lie flat relative to the local water's surface. But
> if that surface is nearly vertical (as in a steep wave), then a capsize is
> imminent unless the paddler attempts an ill-advised down-wave brace (a
> danger for shoulder dislocations). A low primary, high secondary stability
> boat can just edge into the steep wave ever so slightly, ride over it, and
> have no fear of capsize. Again, since I have never paddled a folding kayak
> in rough water, at what point does the high initial stability become a
> drawback in terms of remaining upright?

It will at some point, definitely, be a drawback at about the point the
boat was absolutely vertical on its side and would trip over its
downside sponson. I know that many hardshell kayakers are getting good
at getting their boats on their side and holding a good brace.

But I have seen folding kayaks go over nearly that much and just right
themselves.  For example, it happened to me in my first months of
paddling in my double foldable.  I was going into surf near Coney
Island.  Fiddling with the rudder cord to drop it into the water, I let
the boat get completly sideways to a pretty decent wave.  We went over
quite a bit, no bracing.  I have no real idea of what degree of tilt we
had but fellow experienced paddlers on the beach later said that they
fully expected, from their own experience, that we would be windowshaded
back toward the beach.  Instead the boat righted itself.  I finally got
it pointed into the next wave which broke over our heads and came out
the outer side soaked.

There is no issue that a skinny boat in the hands of a very capable
experienced paddler will do well in chaotic waters because of the superb
bracing, sculling and rolling skills of the paddler using its secondary
stability.  But if you only have limited, less than superb skills when
in such a tippy boat, the secondary stability will mean squat to you and
you will capsize.

In a folding kayak with its flex and stability, you can go into pretty
insane stuff and the boat will help see you through.  Don't get me
wrong...folding kayaks can capsize and do.  But in many instances in
rough conditions, many paddlers have come back reporting that the boat
saw them through without their doing much to keep upright much to their
amazement.

ralph diaz
-- 



From: "Rob Cookson"
Subject: RE: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)
Date: Tue, 12 Sep 2000 09:00:53 -0700

Hi Kevin,

Can you name one instance where two paddlers of like skill were out in rough
water, one in a stable boat and one in a narrow boat, where the narrow boat
remained upright and the stable boat capsized?

Cheers,

--
Rob Cookson
"I like a little rebellion now and then. It is like a storm in the
Atmosphere." Thomas Jefferson in a letter to Abigail Adams, February 22,
1787.



Date: Tue, 12 Sep 2000 09:56:39 -0700
From: Kevin Whilden
Subject: RE: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)

Hi Rob,
You know something... I cannot name a situation like you describe. I also 
cannot name the converse either. It's weird, but I have never been on a sea 
kayak trip where someone has capsized unintentionally outside of the surf 
zone. It seems like I either paddle with people who are very skilled 
whitewater boaters, or in conditions that are very benign. I have capsized 
personally on solo trips, but that doesn't help either. But it sounds like 
you have an opinion on whether high initial stability can become a 
liability, so let's hear it!
Kevin




From: "Rob Cookson"
Subject: RE: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)
Date: Tue, 12 Sep 2000 10:35:09 -0700

Hello again Kevin and All,

All I can offer is what I have observed over the years teaching and leading
tours.  My experience has been that with groups of paddlers with low to
moderate skill levels, the boats of lower stability capsize first.

(Though here's something funny for you, I only had one capsize in all of my
tours this year and he was in a stable single Kayak, less than 20 'from
shore in mirror calm conditions.  He leaned WAYYYY over the side to look at
his rudder and sploosh over he went.)

I would suggest that if you put one expert in a tippy boat and one expert in
a stable boat (both boats that the experts are familiar with) they would
both stay upright until the point of exhaustion and then capsize.  I will
say that with two novices in the same situation I have always seen the
skinny boat capsize first.

The first sea kayak I ever paddled in rough water was a Dirigo, remember
those?  27.5" wide.  I paddled the Dirigo in some pretty rough stuff and
never capsized.  I have also paddled my Dawn Treader in similar conditions
and stayed upright, same same Nordkapp.

I guess there could be a point where too much stability becomes a problem,
it's just that I have never witnessed it.  I have lead people in double
Folbots in conditions that I never would have taken them in in even
moderately beamy singles.  Stability can be an advantage.

As you and I know each other, I think you also know that my preference in
personal boats leans towards skinny tippy little craft.  Why?  Because they
are fun!

If you said: "Rob we're going to drop you into this hurricane and we want
you to survive as long as you can, pick a boat."  I would opt for a Godzilla
or an old Response, both stable and easy to roll and control.  Hey I might
as well have some fun surfing before I go!

Anyway,  just things I've noticed.

Cheers,


Rob Cookson

 "They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety"
Benjamin Franklin




From: [John Winters]
Subject: Re: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)
Date: Tue, 12 Sep 2000 15:23:19 -0400

Rob wrote (or was it Kevin?) :

(SNIP)

>
> I guess there could be a point where too much stability becomes a problem,
> it's just that I have never witnessed it. I have lead people in double
> Folbots in conditions that I never would have taken them in in even
> moderately beamy singles.  Stability can be an advantage.
>

The point where form stability (wide and shallow  vs narrow and deep)
becomes a liability occurs in breaking beam seas. My web site has a
rudimentary discussion of this and you can get the full lowdown in Marchaj's
"Seaworthiness: The Forgotten factor". The form stability increases the
capsizing moment in breaking seas and can overpower the ability of the
paddler to counteract it.

I would guess that most capsizes of folding boats occur during attention
lapses. When paddling canoes (36" wide) in the open ocean I never once had
even a mild concern. Mind, we had fairly heavy loads but the conditions
reached the "impossible to make headway level".

So long as one remains head on to seas, form stability does not cause many
problems. For this reason, those relying upon form stability usually make
use of drogues or sea anchors to keep the boat normal to seas.

This of course, does  not mean that narrow boats work a whole lot better in
these conditions except in the hands of skilled paddlers.

John Winters




From: "Rob Cookson"
Subject: RE: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)
Date: Tue, 12 Sep 2000 12:45:37 -0700

Hi John and All,

> Rob wrote (or was it Kevin?) :

It was me.  Thought this might draw you out-always a good thing. ;)

> The point where form stability (wide and shallow  vs narrow and deep)
> becomes a liability occurs in breaking beam seas. My web site has a
> rudimentary discussion of this and you can get the full lowdown
> in Marchaj's "Seaworthiness: The Forgotten factor". The form stability
> increases the capsizing moment in breaking seas and can overpower the
> ability of the paddler to counteract it.

I have no doubt that this holds true in theory.  It is just that I have
never witnessed it in kayaking.  The only reason I mention it at all is I
have heard members of the cult of the skinny boat tell new paddlers that a
skinny tippy boat is much more seaworthy than one that is more stable.  I
just haven't seen a case where a kayaker was in a boat with such high form
stability that they could not lean it far enough into a breaking wave to
prevent capsize.  Doesn't mean it doesn't happen, I just haven't seen it.

> I would guess that most capsizes of folding boats occur during attention
> lapses. When paddling canoes (36" wide) in the open ocean I never once had
> even a mild concern. Mind, we had fairly heavy loads but the conditions
> reached the "impossible to make headway level".

Attention lapse or worse yet-incorrect response to a given condition, e.g..
leaning away from the wave while doing a high air-brace.

> This of course, does  not mean that narrow boats work a whole lot
> better in these conditions except in the hands of skilled paddlers.

Yup, that's all I'm saying.

Cheers,

--
Rob Cookson




Date: Tue, 12 Sep 2000 16:10:54 -0400
From: Steve Cramer
Subject: Re: [Paddlewise] Instability of folding kayaks (was Re:
  Rollinga K-lite)

Rob Cookson wrote:
> 
> If you said: "Rob we're going to drop you into this hurricane and we want
> you to survive as long as you can, pick a boat."  I would opt for a Godzilla
> or an old Response, both stable and easy to roll and control.  Hey I might
> as well have some fun surfing before I go!

Funny you would say that. I was out in an area of converging waves
Sunday in my Godzilla. Talk about confused seas, waves were hitting me
from literally every direction. A couple of times I was surfed straight
away from the beach. Not big waves, but the clapotis was about eye
height.

The striking thing was, that boat is so stable I didn't need to brace or
even edge much, even when a blindside wave broke right on my shoulder.
Of course if you need to put it on edge, it's no problem to lay your ear
in the water. 

Steve




Date: Tue, 12 Sep 2000 14:14:25 -0600
From: "Shawn W. Baker"
Subject: Re: [Paddlewise] Instability of folding kayaks

Kevin Whilden wrote:

> I have never seen a more confused mixture of  2-3 foot high boils with
> an occasional deep violent whirlpool. Even the hardcore whitewater 
> crazies avoid that place,

Ralph Diaz wrote:

> Sounds ominous.  I would not want to be in that stuff ever.  Who would?

Some people call that fun!

> But I have seen folding kayaks go over nearly that much and just right
> themselves.  

I think it's easier in a narrower boat to regularly practice and
"establish" that tipping point so you know exactly "where" the boat is,
and how it is reacting to the water.  In a very wide ("stable") boat, it
is more difficult to establish that edge.  If you're tilted way up on
edge by an errant wave, you're trusting to the boat's secondary
stability, but not quite sure when and where (and if!) it is going to
kick in.

I'm not knocking folding boats (never paddled one) but I have a harder
time with beamy boats in confused seas than a narrower boat, but that's
just my perception.

Shawn




Date: Tue, 12 Sep 2000 14:20:35 -0600
From: "Shawn W. Baker"
Subject: Re: [Paddlewise] Instability of folding kayaks

Rob Cookson wrote:

> I would suggest that if you put one expert in a tippy boat and one expert in
> a stable boat (both boats that the experts are familiar with) they would
> both stay upright until the point of exhaustion and then capsize.  I will
> say that with two novices in the same situation I have always seen the
> skinny boat capsize first.

But would said expert in the stable boat or said expert in the tippy
boat reach exhaustion first?

Shawn
And after typing that I realized it sounds a lot like the chicken/egg
question.



-- 
Shawn W. Baker




From: [Ralph C. Hoehn]
Date: Tue, 12 Sep 2000 17:04:43 EDT
Subject: Re: [Paddlewise] Instability of folding kayaks

"Shawn W. Baker" writes:

>  .. I think it's easier in a narrower boat to regularly practice and "establish"
>  that tipping point so you know exactly "where" the boat is, and how it is
>  reacting to the water.  ... I'm not knocking folding boats (never paddled one)
>  but I have a harder time with beamy boats in confused seas than a narrower boat,
>  but that's just my perception.

Shawn, that's exactly why, in commenting Ralph Diaz's earlier post, I suggested that
bracing, sculling and rolling practice is a useful "circus act" even in a folding
boat, to be practiced right alongside assisted and unassisted rescues, which is
standard practice in the non-folding kayaking world.

Ralph C. Hoehn




From: "Rob Cookson"
Subject: RE: [Paddlewise] Instability of folding kayaks
Date: Tue, 12 Sep 2000 13:46:16 -0700

Hi Shawn and All,

> But would said expert in the stable boat or said expert in the tippy
> boat reach exhaustion first?

Ya got me Shawn.  Too many variables for my small brain.  Guess it all comes
down to a my expert is better than your expert contest.

I think the bottom line is find a boat that suits your needs and have fun.

> Shawn
> And after typing that I realized it sounds a lot like the chicken/egg
> question.

By the way...

I think the good Doctor Inverbon knows the answer to the chicken and egg
question.  Perhaps his humble scribe could relay our burning curiosity to
him.

Cheers,

--
Rob Cookson




Date: Tue, 12 Sep 2000 22:21:25 -0400
From: Gabriel L Romeu
Subject: Re: [Paddlewise] Instability of folding kayaks

I was in my rather narrow boat with a couple of people in those wider,
stabler boats(a Romany and a Baja) having a conversation (stationary) on
the Delaware river a couple of weeks ago, A rather large boat wake swept
us up.  my boat went up and down very vertically while theirs swaggered
from side to side, I'm sure that they subconsciously compensated with
weight shifts.  
I think dealing with this in rather turbulent waters for any length of
time could be fatiguing, even more so in a boat with a firm initial
stability.
It seems that my boat has no primary stability and it requires very
little effort to put and maintain a edge for a length of time.  I am not
fighting that primary stability.

-- 

Gabriel L Romeu 




From: Peter Osman
Date: Wed, 13 Sep 2000 22:00:37 +1100

Rob Cookson wrote: -

> I would suggest that if you put one expert in a tippy boat and one expert
> in a stable boat (both boats that the experts are familiar with) they would
> both stay upright until the point of exhaustion and then capsize.  I will
> say that with two novices in the same situation I have always seen the
> skinny boat capsize first.

G'Day Rob,

What you say is consistent with my experience. I'm a novice who paddles both
a Klepper Aerius single and a skinny small cockpit boat called a Pittarak. 
Both are delightful. In 3 foot chop the Klepper gives an effortless ride, in
the Pittarak when it is unloaded, the same chop requires me to exert a
conscious level of knee lift and very occasional bracing. The Klepper has both
good primary and secondary stability while the unloaded Pittarak has good secondary
stability. I'm told that when loaded it has good primary stability as well. I can
sometimes roll the Pittarak but not the Klepper and the Pittarak is faster. Larry
Gray, The designer of the Pittarak, can roll both with no modifications to either,
he is most definitely an expert.

For extended trips off shore and at my present level of skill I would choose
the Klepper. When I am more skilled and in the company of fast paddlers I will
use the Pittarak.

All the best, PeterO




From: "John Winters"
Subject: Re: [Paddlewise] Instability of folding kayaks (was Re: Rolling
  a K-lite)
Date: Wed, 13 Sep 2000 20:50:15 -0400

Rob wrote:
>
> I have no doubt that this holds true in theory.  It is just that I have
> never witnessed it in kayaking.  The only reason I mention it at all is I
> have heard members of the cult of the skinny boat tell new paddlers that a
> skinny tippy boat is much more seaworthy than one that is more stable.  I
> just haven't seen a case where a kayaker was in a boat with such high form
> stability that they could not lean it far enough into a breaking wave to
> prevent capsize.  Doesn't mean it doesn't happen, I just haven't seen it.

Most of the people who paddle in these conditions have a lot of skill (at
least the ones who survive :-)) and I confess that I try to avoid such
conditions as much as possible although avoidance does pose problems in the
North Atlantic. To get an idea of the conditions try side surfing into a
beach in plunging breakers. :-0

> Attention lapse or worse yet-incorrect response to a given condition, e.g..
> leaning away from the wave while doing a high air-brace.

No doubt. You can find a good story about what happens in Hannes Lindemann's
"Alone at Sea" . He capsized when his sea anchor line failed. Drifted
sideways and capsized. Of course, this had nothing to do with a lack of
skill. He was sleeping at the time I think.

>
> > This of course, does  not mean that narrow boats work a whole lot
> > better in these conditions except in the hands of skilled paddlers.
>
> Yup, that's all I'm saying.

Yes, I think a lot of people leap to conclusions about what "is best" as
universal rule when it really amounts to "what works best for me and what I
do". So long as paddlers recognise the down side of a boat's stability
characteristics and allow for it they can stay out of trouble. Low form
stability boats require generally higher skill levels and more constant
attention most of the time while high form stability boats can lull one into
a false sense of security and require either a lot of attention in breaking
seas or some other means of keeping the boat normal the the sea train.

You pays your money and takes your choice.

Cheers,

John Winters




From: [John Winters]
Subject: [Paddlewise] Stability
Date: Fri, 15 Sep 2000 08:25:26 -0400

I didn't have much time when I wrote my last post on this topic so left out
a lot. Some of you may find this interesting

Most articles about sea kayak stability have a diagram showing a wide kayak
that heels to follow the slope of the wave and a narrow kayak that remains
more upright. The text with the diagram usually suggests that the same
stability that makes a boat feel comfortable in flat water contributes to
capsizing in waves. Unfortunately this often misleads readers.

The water molecules in a non breaking wave travel roughly in circular orbits
around the center of the wave. This results in centrifugal force that, in
conjunction with normal gravitational force produces an apparent
gravitational force acting normal to the wave surface. Some call this the
"local" gravity and I am indebted to Bruce Winterbon for the term "apparent
gravity" which makes more sense to me. The combined forces cause the "shape"
of the wave.

A blindfolded paddler in a boat lying parallel to the wave will not sense
any heeling moment (although they may sense some motion) even though the
wave surface may have a significant slope. This causes a problem for
paddlers. Even though they may sense no heel they perceive heel visually by
observing the horizon. In response they heel the boat into the wave and in
so doing actually create a capsizing moment where none existed. You can test
this phenomenon best by observing a plumb bob against the horizon while
sitting still in a life raft.

I believe that this phenomenon may have contributed to capsizes caused by
what some researchers called "kayak angst" suffered by Inuit who paddled for
long periods of time. The paddler would sense heel visually, correct against
the apparent gravity and capsize. No doubt modern paddlers could have the
same problem.

Once the wave breaks, the situation alters as the rotational motion of the
water molecules changes to translational motion which can cause a capsizing
moment proportional to the righting arm of the boat. Note the term righting
arm rather than righting moment. Righting moment  is the product of the
righting arm and  displacement and acts to orient the boat to the surface.
The righting arm is a function of the boat's shape and center of gravity
without consideration for displacement. Of two boats with the same righting
arm, the heavier will have more stability or righting moment.

This difference between righting arm and righting moment leads to another
interesting and sometimes confusing aspect of stability. Due to the
centrifugal force, the apparent gravitational force varies with location on
the wave. For example, the apparent gravitational force on the trough
exceeds that of the force at the crest. Ocean sailors may have some
familiarity with this for boats heel more on the crests than in the troughs
(more than the variable wind force causes).

I have read some suggestions that, given a large enough and steep enough
wave, that the centrifugal force could counteract all gravitational force
resulting in  no righting moment even while fully upright. This explains the
greater capsize vulnerability of boats in breaking beam seas and why a
strong brace becomes such a useful weapon in avoiding capsize for any boat.

So,  returning to my earlier comment about the diagrams in magazines etc., a
more appropriate diagram would show the two boats in breaking seas  not
smooth seas and the explanation should point out that the increased capsize
moment only applies to breaking seas and/or confusion resulting from horizon
and apparent gravity providing confusing signals to the paddler about her
orientation.

John Winters

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