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From: Robert Livingston & Pam Martin <bearboat2_at_attbi.com>
subject: [Paddlewise] paddlefloat photo
Date: Fri, 28 Dec 2001 07:04:33 -0800
> I'll bet that whining noise I'm hearing is all
> the rolling freaks whining about not being able to lay back on the back
> deck. Still, I would find the back support welcome for normal paddling.

Interestingly enough, I was first inspired 20 years ago to put a hump on my
kayak primarily to lean against. Its other advantages were secondary.  My
early boats with the design, however, all ended up with the hump too far
back to actually lean against and I was young enough that I did not really
care much one way or another. This is the first one that I can comfortably
lean against the hump. Amongst friends I will confess that I occasionally do
just that, though I know it is poor form.

This kayak rolls exceedingly easily because of the buoyancy of the hump. My
9 yo son can roll it with his hands. For rolling, there are alternate
positions that allow rolling to be accomplished quite handily (so to speak).

The hump is a disadvantage when trying to get back into the boat from the
water, if you do not do a reentry and roll. Most reentry scenarios place the
body, at one time or another, low over the back deck which is obviously not
possible with this design.  

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From: Matt Broze <mkayaks_at_oz.net>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sat, 22 Dec 2001 17:35:35 -0800
The Eddyline Falcon must be a pretty rare bird (as kayaks go) to not get any
tippier when flooded with water. Perhaps that is because it has no stability
to begin with so adding water doesn't change anything. This is not just idle
speculation on my part. Sea Kayaker magazine's review found that the empty
Falcon 16 had no inherent stability. The curve started at zero (like all
stability curves do) but then went down from there instead of rising into
positive territory first as most stability curves do. I guess maybe I will
form this working hypothesis. "The less initial stability a hull has the
less the stability will be affected by swamping it." Does anyone have any
experiences which would tend to cast doubt on it?

BTW in Ken's photos I don't think his shoulder is in an especially
vulnerable position since his weight is being transferred pretty much
straight down his arm to the paddle shaft. A sudden lifting of the
paddlefloat would not lift the shoulder joint out of the socket (as it can
in a HIGH brace in the rear quadrant) and his arm is free to bend at the
elbow if need be to limit the forces pushing on his shoulder. (Note one
reason a LOW brace in surf can be dangerous is that if the arm is forced up
and back it is difficult to let go of the paddle with that hand position or
bend the arm (without also putting more force rotating the shoulder back). I
have a friend who tore his rotator cuff just this way.)

For those who are confused by not seeing the original, below is the full
text of the note I sent to Ken (but not yet to Paddlewise--that he snipped
some and responded to on paddlewise). This is the unsnipped version.

Ken wrote:
>>>>>>Several weeks ago I started a thread on the paddlefloat rescue which
elicited
a lot of comment.  Rex Roberton took an excellent photo of the homemade
float
which I've posted on our website.  (Thanks Rex!)  You can see the photo, and
also see a description, with photos, of the method I use to do a 30 second
rescue.  (And no, that doesn't include pumping--I carry the boatfull of
water
with me as a reminder to be more careful in the future!)  The web address is
www.kayakfit.com .  Scroll down the menu until you find the link to the
Paddlefloat Rescue, and click on it.<<<<<<

I saw the pictures and directions on your website of the paddle float
rescue. Your technique for the untethered paddle paddlefloat rescue looked
good. I think it is a valuable method to learn especially for a surf zone
rescue where shore is nearby and you are not going to have to pump out (and
want to be able to disassemble the boat and paddle at a moments notice
before the breaker hits too). However, I'd suggest you go out on a rough day
and do this rescue (in a safe place with onshore wind) before you promote it
as the "be all, end all" of paddle float rescues (but then don't even pump
out the kayak in calm the pool afterwards--and dismiss that lack of
finishing the rescue with the joke above).
I think you will find that if you fasten the paddle firmly to the back deck
you will get the pumping out process done so much quicker (if you can get
the spraydeck on and pump out the now very unstable swamped kayak at all
without capsizing again) especially in rough water. Rough water, like the
kind that probably would contribute to your capsizing, by accident, in the
first place. Fastening the paddle to the deck may take a few more seconds
but I'll bet you can make up much of that time by climbing up onto the kayak
from in front of the paddle and not having to carefully pivot over the
paddle while moving one hand and one foot at a time (to keep it held in
position while getting your feet around and back into the cockpit--something
BTW that is also a lot easier to do in a calm pool than in rough water).
I agree that foam floats can save 40 seconds or more of in the water time
compared with an empty inflatable paddle float, but personally, I don't want
to have to put up with the bulk of the foam during all the times when I
don't need it. Have you made your foam float with a way to just grab it off
the deck and roll up with when you capsize and fail to roll (so you won't
have to exit the cockpit)? It seems if one is going to have to put up with
the bulk anyway you should at least be able to use it to do a float roll and
save all that pumping time in compensation. Again because I roll pretty
reliably and don't want the bulk I don't usually leave my inflatable paddle
float partly inflated and easy to grab (and pull free for a float roll)
either, but some folks do. I always could leave it inflated, if I wanted to,
(like maybe after having already had to do one paddlefloat rescue and not
wanting to have to pump out all that water again). You bet then I'll stuff
that partly inflated paddle float under my front bungies and be ready to go
for a Float Roll if I miss my roll again anytime soon.
Yes, I think the (no paddle) Float Roll is definitely a technique worth
learning especially so if you are roll challenged. I also think you should
be ready to fasten the paddle firmly to your deck should that be the best
option (which I think it usually is, and as folks who try to pump or put
their spraydeck back on, while bracing at the same time, soon find out).
Everybody: Do you have a tether on your paddle float so it can't float or
blow away if you drop it? Ken, do you depend on keeping yours secure under
deck lines until it has been secured firmly on the paddle blade (rather than
use a tether) or do you use both?

Matt Broze
http://www.marinerkayaks.com


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From: Robert Livingston & Pam Martin <bearboat2_at_attbi.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sat, 22 Dec 2001 21:33:34 -0800
> Does anyone have any
> experiences which would tend to cast doubt on it?

Yes.  The Ursa 350.  :)

 This kayak has three features that make it stable when there is water in
the center area where the paddler sits.

The first is a large amount of flare which comes down into the water as the
boat gets heavier,

The second is that the rear bulkhead wraps around the paddler so that the
kayak retains an air pocket on each side of his/her thighs (a continuation
of the rear compartment) - Dare we say built-in "sponson"?

The third is that there is a central extension of the paddler compartment
that extends back low in the midline, invaginating the posterior
compartment. (Designed for holding shoes) When this fills with water it
places additional weight in the mid-line with air on each side.


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From: Michael Daly <michaeldaly_at_rogers.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 01:37:51 -0500
From: "Robert Livingston & Pam Martin" <bearboat2_at_attbi.com>

> > Does anyone have any
> > experiences which would tend to cast doubt on it?
> 
> Yes.  The Ursa 350.  :)
> 
>  This kayak has three features that make it stable when there is water in
> the center area where the paddler sits.

 [order switched...]

> The second is that the rear bulkhead wraps around the paddler so that the
> kayak retains an air pocket on each side of his/her thighs (a continuation
> of the rear compartment) - Dare we say built-in "sponson"?

This can provide additional bouyancy to prevent sinking, but it will not contribute
to stability.  The water on the outside of the hull doesn't know what's inside the
hull.  Adding a sponson to the _outside_ of a hull can make a difference.

> The first is a large amount of flare which comes down into the water as the
> boat gets heavier,
> 
> The third is that there is a central extension of the paddler compartment
> that extends back low in the midline, invaginating the posterior
> compartment. (Designed for holding shoes) When this fills with water it
> places additional weight in the mid-line with air on each side.

These two assume there are no free surface effects.  I rather doubt that any kayak
will be more stable when flooded.  If the kayak heels, the water is free to move
to a new position.  Unless you've got lots of baffling to prevent the water from moving
around, you're in trouble.  If you've got sufficient baffling, you've got nowhere to sit!

I thought we've been over this before?  And the conclusion every time is the same:
flooding a kayak is a bad thing.

Mike

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From: Robert Livingston & Pam Martin <bearboat2_at_attbi.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 02:59:47 -0800
> This can provide additional bouyancy to prevent sinking, but it will not
> contribute
> to stability.  The water on the outside of the hull doesn't know what's inside
> the
> hull.  Adding a sponson to the _outside_ of a hull can make a difference.

Speaking of what water "knows".

If you have a sponson on the outside of a hull how does the water "know"
that it is not the outside of the hull itself?

Say you "glue" that sponson to the outside of the hull. How does the water
know that this is a sponson on the outside of the hull rather than just a
bulge in the contour of the hull.

What if you are paddling a Klepper like the old one that I used to have that
used an air-bag to tighten the skin and this air bag ran around the hull
like a sponson. What does the water think of this? That air bag was "inside"
the hull.

--------------------

The reason the water "knows" about the built in sponson is that as the
partially flooded boat starts to tip the water is restrained from going to
the edge of the outside hull "within" the boat. The otherwise freely mobile
water is constrained to stay in the center of the boat because the edges are
full of air.


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From: Michael Daly <michaeldaly_at_rogers.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 12:35:56 -0500
From: "Robert Livingston & Pam Martin" <bearboat2_at_attbi.com>

> > This can provide additional bouyancy to prevent sinking, but it will not contribute
> > to stability.  The water on the outside of the hull doesn't know what's inside the
> > hull.  Adding a sponson to the _outside_ of a hull can make a difference.
> 
> Speaking of what water "knows".
> 
> If you have a sponson on the outside of a hull how does the water "know"
> that it is not the outside of the hull itself?

In this case, the sponsons effectively change the shape of the hull, creating a hull
with greater stability than the original hull.  

> Say you "glue" that sponson to the outside of the hull. How does the water
> know that this is a sponson on the outside of the hull rather than just a
> bulge in the contour of the hull.

Ditto

> What if you are paddling a Klepper like the old one that I used to have that
> used an air-bag to tighten the skin and this air bag ran around the hull
> like a sponson. What does the water think of this? That air bag was "inside"
> the hull.

If inflating the sponson changes the shape of the hull, it will have an effect.  If not,
the water outside won't know the difference.  In a rigid hull, what you change inside
is irrelevant.

> The reason the water "knows" about the built in sponson is that as the
> partially flooded boat starts to tip the water is restrained from going to
> the edge of the outside hull "within" the boat. The otherwise freely mobile
> water is constrained to stay in the center of the boat because the edges are
> full of air.

Peter Rathman's also pointed this out.  It is the exception and is valid.  However, 
this represents a small portion of the total cockpit volume.  Stability comes from
the center of gravity changing at a slower rate with heel angle than the shift in the
center of bouyancy.  If the water is free to move, the center of gravity shifts faster
than would a dead load.  This reduces or eliminates stability.  Internal sponsons
don't kick in until the heel angle is relatively high and most of the water has already
moved.  I've only seen the sponsons on a Khat S - I can't imagine that Kleppers
are so different that the behavior would be favorable.

Also PeterO's comment about his Klepper brings to mind the possibility that in 
foldables and skin on frame designs, the internal ribs act as baffling and can help.
However, these also contribute only a small amount and would only affect the 
kayak if the water is not deeper than the ribs, keelson etc.  

If there is a design that significantly changes the behavior of water internally, I'd like to 
know how it works.

Mike

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From: Mike McNally <mmcnally3_at_prodigy.net>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 16:39:17 -0600
What water knows...  I think you all are missing something which can be
clearly seen from a proper free body diagram (let's hope I can draw one).  

                                Wt-W&Y (wt of water & you & yer stuff)
  
                                  |
                                  |
                                  |
                                  |
                                  |
                                  |
                                  |
                                  |
                                  V  
          -------------------------------------------------         
                 ^                ^                ^
                 |                |                |
                 |<- - - - - - - >|                |
                 |       dx       |                |
                                  |                 
                S_L               |               S_R (sponson, right)
                                  |                  
                                  |                  
                                  |                 
                                  |                 
 
                                 B_E (bouancy from ends)

These forces are all algebraic functions varing in both magnitude and 
direction realitive to the angle of tip (ex tip gives slosh & shifts
center of mass).  But, the basic geometry tells us a few things.  The
difference between interior and exterior sponsons is the distance dx,
where the turning moment from force S_L=(in the simplest case) F*dx.

The hull stability forces from the hull design are largely made
null by the evacution of air from the hull, hence the lack of stability,
but now that we are adding more air and particulary adding it in a
manner in which the dist dx is set (superior to what a seasock does), we 
are increasing these previously insignificant forces of stability
provided by the hull.  

Catch 22 is: we know the significant quantity of air in the ends isn't
doing much for us, stability wise, so we are going to have to very
significantly replace water with air.  The design as initially described
did not seem to be doing this, so I don't disagree with other posters in
the sense that the forces I'm discussing here wouldn't provide much
change in stability, in that particular design.  But, with a more
significant interior sponson it would provide the flooded state
stability we are looking for.  I think in the future we will see this
design incorporated in many boats.  

With the completion of this post I do hereby declare myself the
sovereign pope of the church of the interior sponson.  You may not here
from me for a while because I'm feeling an almost unquenchable desire to
post on rec.boats.paddle.  gotta go

-- 
Mike McNally		mmcnally3_at_prodigy.net

You are capable of planning your future.

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From: Robert Livingston & Pam Martin <bearboat2_at_attbi.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 03:04:26 -0800
> These two assume there are no free surface effects.  I rather doubt that any
> kayak
> will be more stable when flooded.  If the kayak heels, the water is free to
> move
> to a new position.  Unless you've got lots of baffling to prevent the water
> from moving
> around, you're in trouble.  If you've got sufficient baffling, you've got
> nowhere to sit!


If the flare continues to the rear of the boat and to the bow it encompasses
the area behind the rear bulkhead and in front of the front bulkhead.
Therefore the free surface affects do not cancel out the increased width at
the waterline as a markedly flared boat settles down into the water. Only if
the boat has no bulkheads is what you say true.


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From: Michael Daly <michaeldaly_at_rogers.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 12:53:14 -0500
From: "Robert Livingston & Pam Martin" <bearboat2_at_attbi.com>

> > These two assume there are no free surface effects.  I rather doubt that any  kayak
> > will be more stable when flooded.  If the kayak heels, the water is free to move
> > to a new position.  Unless you've got lots of baffling to prevent the water from moving
> > around, you're in trouble.  If you've got sufficient baffling, you've got nowhere to sit!
> 
> If the flare continues to the rear of the boat and to the bow it encompasses
> the area behind the rear bulkhead and in front of the front bulkhead.
> Therefore the free surface affects do not cancel out the increased width at
> the waterline as a markedly flared boat settles down into the water. Only if
> the boat has no bulkheads is what you say true.

I don't think I'd go that far.  The cockpit volume is a significant portion of the 
total volume of the kayak.  It also represents the greatest width in most designs.
It is true that the lowering of the CG due to the increased weight will increase
the stability of the ends, but this may be offset by the amount of decrease in
the cockpit.  My experience in flooding kayaks and paddling them suggests 
the benefit isn't there.  I haven't done this with a significantly flared hull, though.  
My Ellesmere has such a hull; I'll give it a try in the pool this coming Feb. and see.

Mike

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From: Robert Livingston & Pam Martin <bearboat2_at_attbi.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 03:14:22 -0800
> I thought we've been over this before?  And the conclusion every time is the
> same:
> flooding a kayak is a bad thing.

I would not argue this, at least where I paddle.  Stability issues aside it
is cold. I would not suggest that someone deliberately flood their boat
because they are unstable. The issue is when you find yourself with a
partially flooded boat just how bad a situation are you in. It varies with
the design of the boat.

 I was just answering Matt's comment that only a boat that is very unstable
to start with will not have a marked decrease in stability when flooded.
There are boat designs and construction techniques  possible that would
argue against that statement. These are "atypical" boats.

Also if Matt's statement was meant to imply that ALL the compartments of the
boat are flooded (i.e. there are no or effectively no bulkheads then it
would be hard to argue although a Klepper-like situation with a large
internal stiffening airbag would be more stable than one without.


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From: Bob Denton <gulfstream_at_flinet.com>
subject: RE: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 12:41:33 -0500
I own a Falcon 16 in light lay-up (34lbs)and have never noticed any
stability issues. It may be my weight (180 lbs). It's more stable than
my Nordkapp and handles rough water well. The curves seem to be a bit
misleading with this boat.

cu



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From: Peter Rathmann <prathman_at_attbi.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 14:50:03 -0800
Michael Daly wrote: 
> From: "Peter Rathmann" <prathman_at_attbi.com>
> > To the extent that [internal sponsons] keep interior water from sloshing to the
> > sides of the boat they will certainly aid the stability relative to a
> > boat of the same shape that lacks internal sponsons.
> 
> True, but the effect may be small and only kick in a higher angles of heel.
> I'm not sure that the effect would be enough to brag about.

The size of the effect would depend on the particular design and could
vary from very small to large.  Before you argued that there was no
effect at all of internal sponsons on stability of a flooded boat and my
post was primarily to point out that there was indeed such an effect.  
> Having
> deliberately flooded a couple of kayak in a pool, I know that the reduction
> of stability is tremendous and I don't think a sponson's several liters of
> volume (compared to the, say 150+ liter cockpit volume) is going to make a
> big enough difference.

Who said they were only a few liters?  This is again a question of the
specific design and internal sponsons that occupy all the space on the
sides of a wide cockpit could easily constitute a high percentage of the
total original (unsponsoned) cockpit volume.
> 
> A snug sea sock may be the alternative.  There the volume is constrained and
> if the sock can't slide sideways, the water is better constrained.

Again, there is no reason why the internal sponsons couldn't occupy all
the space that is outside the seasock.  I would expect the sponson
approach would actually be easier to make in a way that would constrain
water movement, but that is also a question of design details.  If you
believe that a properly fitted sea sock could add to stability in a
flooded boat, then similarly fitted internal
sponsons/bulkheads/'whatever you want to call them' can certainly do the
same thing. As you said before, the water can't tell the difference.

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From: Michael Daly <michaeldaly_at_rogers.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Sun, 23 Dec 2001 23:06:25 -0500
From: "Peter Rathmann" <prathman_at_attbi.com>

> water movement, but that is also a question of design details.  If you
> believe that a properly fitted sea sock could add to stability in a
> flooded boat, then similarly fitted internal
> sponsons/bulkheads/'whatever you want to call them' can certainly do the
> same thing. As you said before, the water can't tell the difference.

I wouldn't say that it adds to stability.  It minimizes the reduction of stability.
That may sound like semantics, but I don't think so.

In general, what you say is true, however, I've been thinking in terms of the 
sponsons that I've been seeing in real kayaks.  These tend to be small.  

I think there's been a difference in perspective between me and others, including
yourself.  I've been taking a sort-of pragmatic, "is it good enough?" view considering
kayaks I've seen or paddled, whereas others have been saying "does it happen at
all?" with atypical or theoretical kayaks.   We have both come to different conclusions, 
but to different questions.   In the context of the original discussion, I may be off base.

In terms of "good enough", sponsons in real kayaks contribute to reserve flotation,
not stability.

Minimizing the amount of water in the cockpit is a good thing.  That's one 
reason I've replaced the forward bulkhead in my Solstice to one that
is further aft.  However, the water remains a destabilizing effect.  Whether you
remove the volume forward or laterally, you still improve the situation.  I'm
not ready to say that it's enough to make an unstable kayak stable.  I've paddled
kayaks with negligible reserve stability with only a couple of inches of water
inside and both fore and aft compartments empty.  In a kayak like that,
a sponson or any other trick would have little effect at all.

The main reason I moved my Solstice's bulkhead, however, was to reduce the 
amount of water I'd have to pump and give myself more dry storage forward.  
My tests since then have confirmed that it doesn't yeild a significant 
improvement in retaining stability.

I can't imagine taking my Ellesmere and adding internal flotation that would
have a great effect.  There's little room between the seat and the hull on the
sides.  I could take up volume around my legs, but it would have to be 
planned with ease of entry and exit in mind.  In the end I doubt that a 
significant improvement in flooded stability would be there.  An improvement,
but not significant enough for me to bother.  If you're talking about a kayak
with a 28 inch beam, that would be different, but that's not a typical kayak.

Mike



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From: Matt Broze <mkayaks_at_oz.net>
subject: Re: [Paddlewise] paddlefloat photo
Date: Tue, 25 Dec 2001 22:16:30 -0800
Having started this thread by asking for criticism of my hypothesis, let me
say that I agree with everything Robert Livingston had to say in his
comments. His Ursa 350 is however a very rare "bear" in the kayak world (but
it does point out that my hypothesis needs to be qualified to exclude
certain features found on a few kayaks. I had forgotten and not considered
some of the unique features of the Ursa 350 when I proposed my hypothesis.
While Robert's description was accurate it may have been very hard to
picture the kayak he was describing. This isn't your everyday run of the
mill looking kayak!

Robert, is there somewhere a picture of an Ursa 350 is posted on a website
so that everyone can see the rather strange looking kayak we are talking
about? If not, I could forward some photos of an unfinished hull (with your
approval and if not too many folks ask for them--back channel--so please
wait to ask me to send them until Robert responds about a website and
permission).

Robert designed the Ursa 350 himself using the kayak design program (he also
wrote) that can be downloaded from our website. Another feature of the Ursa
350 that is extremely rare, if not unique, is that one person can bail the
flooded kayak (when out of the cockpit) by simply rolling the kayak over in
the water and spilling the water out of the cockpit (which is suspended
above the sea when it is floating upside down--at least when empty--I'm not
sure about with a gear load). The 350 stands for 350 centimeters (11' 6")
long. As far as I know it is not (yet?) a commercially available kayak (or
if it will ever be made available to the public?).

Matt Broze
http://www.marinerkayaks.com


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From: Robert Livingston & Pam Martin <bearboat2_at_attbi.com>
subject: Re: [Paddlewise] paddlefloat photo
Date: Thu, 27 Dec 2001 11:21:58 -0800
> Robert, is there somewhere a picture of an Ursa 350 is posted on a website
> so that everyone can see the rather strange looking kayak we are talking
> about?


http://homepage.mac.com/rlivingston/

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From: Wes Boyd <boydwe_at_dmci.net>
subject: Re: [Paddlewise] paddlefloat photo
Date: Thu, 27 Dec 2001 15:06:57
At 11:21 AM 12/27/01 -0800, Robert Livingston & Pam Martin wrote:
>> Robert, is there somewhere a picture of an Ursa 350 is posted on a website
>> so that everyone can see the rather strange looking kayak we are talking
>> about?
>
>
>http://homepage.mac.com/rlivingston/

Interesting, and representative of some out of the box thinking from what I
can see. Is there a side view online somewhere?

-- Wes
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