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From: <superiorvisions_at_att.net>
subject: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 21:39:15 +0000
This is a response to the kevlar thread.
I have found that Kevlar is a few ponds lighter than 
fiberglass but that it does not have the rigidity of 
fiberglass. If you want a boat made of an exotic fiber 
like kevlar I recommend that you buy a carbon and kevlar 
kayak. The carbon fibers will run one direction and the 
kevlar fibers will run in the opposite direction. That 
way you will have the rigidity and lightness of carbon 
in the same sheet as the flexible kevlar fibers.

Another concern is how easy damage to a kayak will be.
Working with fiberglass is easier than working with 
carbon or kevlar.

Good Paddling,
Don Dimond 
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From: John Winters <735769_at_ican.net>
subject: Re: [Paddlewise] Slamming
Date: Sat, 13 Mar 1999 09:37:06 -0500
I have done the calculations using Lloyd's standards and most sea kayaks
(and canoes) get over designed due to stiffness requirements. In other
words a boat designed to have only enough strength for slamming loads would
not have enough rigidity to maintain its shape.

Of course, I assumed a properly constructed boat. Not all builders get the
hull/deck joints right etc. so what one boat does should not suggest that
all boats will do the same.

Like ships, the biggest danger to sea kayaks is impact with something hard.
Anecdotal evidence can be found to support the magical qualities of any
material but no one can really calculate how strong "strong" should be
since no one really knows the magnitude of potential loads.

I suspect most reputable builders produce boats suitable for the intended
use. If you want more, then I am sure you can find a builder that can
supply it. As for dropping boats off the roof, I have done one
manufacturer's boats in Royalex, Royalite, Fiberglass, Kevlar, Spectra etc.
In every case the boats survived the 20' drop just fine with some
scratching. I do not think the results unusual at all but I do think that
boats don't often fall off the factory roof in actual use.

I once watched Darryl Lideigh of Mohawk canoes pound on one of his chopped
fiberglass canoes with a hammer. The boat stood up just fine. Not sure what
that proved. Real life proves more.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/




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From: Robert C. Cline <rcline_at_onramp.net>
subject: Re: [Paddlewise] Slamming
Date: Sat, 13 Mar 1999 16:53:31 -0600
I avoided the purchase of a Kevlar boat basically because of the danger of
cracks in the gelcoat.  In fact, I passed up "the deal of the century."
So, this doesn't really matter except for cosmetic reasons?

Is Kevlar "stronger" than fiberglass or is it just lighter?

Robert
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From: Richard Culpeper <culpeper_at_norlink.net>
subject: Re: [Paddlewise] Slamming
Date: Sat, 13 Mar 1999 21:31:46 -0500
John Winters wrote:
--snip--

> I once watched Darryl Lideigh of Mohawk canoes pound on one of his chopped
> fiberglass canoes with a hammer. The boat stood up just fine. Not sure what
> that proved. Real life proves more.

The message seems pretty clear to me.  If you see a Mohawk canoe, start beating
on it with whatever tools of destruction you have at hand.

Cheers,
Richard Culpeper
www.geocities.com/~culpeper

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From: John Winters <735769_at_ican.net>
subject: Re: [Paddlewise] Slamming
Date: Sat, 13 Mar 1999 10:11:22 -0500
-----Original Message-----
From: rdiaz_at_ix.netcom.com <rdiaz_at_ix.netcom.com>
To: paddlewise_at_lists.intelenet.net <paddlewise_at_lists.intelenet.net>
Date: March 12, 1999 11:44 PM
Subject: Re: [Paddlewise] Slamming



>I hope I am not starting a holy war but I doubt that any hardshell
>manufacturer would want to drop a nice fiberglass kayak off of a factory
>roof.  The gelcoat would break off in pieces and scatter like the
>contents of a large spilled package of Chiclets.  Artistic patterns of
>stress fractures would radiate across the hull, et al.

OH gee Ralph. You shouldn't start a war with so little ammunition. One
experience does not make a universal truth not to mention the cosmetic
nature of stress cracks in the gel coat. I know of no one who ever drowned
because their gel coat had stress cracks. The gel coat has a cosmetic value
not a structural value.  As one who has done the drop test as well as a few
others I can say with some authority that you are a tad off the mark on
this.

No one has greater respect for the strength of folding boats than I but I
have also done a lot of crash and bang on a lot of other materials that
stood up just fine. Stronger doesn't necessarily mean better it just means
stronger.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/






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From: Larry Bliven <foxhill_at_shore.intercom.net>
subject: Re: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 10:15:16 -0500
hey there,

>The message seems pretty clear to me.  If you see a Mohawk canoe, start
beating
on it with whatever tools of destruction you have at hand.

i had one of those as my first canoe back in the '70s. we beat the hell out
of it and it held up fine. got my 10 g worth of fun.

a few years ago, i was going to sell it to a friend for $20 - however the
local canoe/kayak shop offered me $200 for it sight unseen. i said no deal
till you see it. he saw it and gave me a check. i only paid about $230 for
it... the dealer cleaned it up and sold it within a week.

don't you just hate paddle shop dealers?


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From: Richard Culpeper <culpeper_at_norlink.net>
subject: Re: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 17:43:15 -0500
Of course when you began negotiating with the dealer you started with "look
into my eyes...you're feeling sleepy."  You really should not use you powers to
take adantage of unsuspecting dealer like that.

Cheers,
Richard Culpeper

Larry Bliven wrote:

> hey there,
>
> >The message seems pretty clear to me.  If you see a Mohawk canoe, start
> beating
> on it with whatever tools of destruction you have at hand.
>
> i had one of those as my first canoe back in the '70s. we beat the hell out
> of it and it held up fine. got my 10 g worth of fun.
>
> a few years ago, i was going to sell it to a friend for $20 - however the
> local canoe/kayak shop offered me $200 for it sight unseen. i said no deal
> till you see it. he saw it and gave me a check. i only paid about $230 for
> it... the dealer cleaned it up and sold it within a week.
>
> don't you just hate paddle shop dealers?
>
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From: Larry Bliven <foxhill_at_shore.intercom.net>
subject: Re: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 10:27:25 -0500
Ooops,

that wasn't a chopped fiberglass Mohawk... i remember seeing the weave of
cloth under the fine gel coat finish.

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From: John Winters <735769_at_ican.net>
subject: Re: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 12:10:21 -0500
-----Original Message-----
From: Robert C. Cline <rcline_at_onramp.net>
To: John Winters <735769_at_ican.net>; paddlewise_at_lists.intelenet.net
<paddlewise_at_lists.intelenet.net>
Date: March 13, 1999 5:44 PM
Subject: Re: [Paddlewise] Slamming


>I avoided the purchase of a Kevlar boat basically because of the danger of
>cracks in the gelcoat.  In fact, I passed up "the deal of the century."
>So, this doesn't really matter except for cosmetic reasons?

Star cracks can appear in Fiberglass, Kevlar, Spectra layups. Gel coat has
little strength but must be applied fairly thickly to assure that the gel
will not lift, alligator, or fail to cover the substrate. If gel coat had
the properties of, say, polyurrethane paints, no star cracking would occur.
It cracks because of a lack of fiber support within the film
>
>Is Kevlar "stronger" than fiberglass or is it just lighter?

Both.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/



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From: John Winters <735769_at_ican.net>
subject: Re: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 19:24:22 -0500
Don wrote;


>This is a response to the kevlar thread.
>I have found that Kevlar is a few ponds lighter than
>fiberglass but that it does not have the rigidity of
>fiberglass.

Quite true. Many builders using Kevlar use cores to stiffen the panels.
Cores also have problems and ductile syntactic foam cores seem to perform
best where impacts might be expected while some of the sheet foams and
honeycombs provide the greatest weight savings. I have an 18 pound 17'
kayak that has stood up just fine for the past three years but I sure don't
hit anything with it. :-)

>If you want a boat made of an exotic fiber
>like Kevlar I recommend that you buy a carbon and Kevlar
>kayak. The carbon fibers will run one direction and the
>Kevlar fibers will run in the opposite direction. That
>way you will have the rigidity and lightness of carbon
>in the same sheet as the flexible Kevlar fibers.

True also. One word of caution. Ideally the builder will sandwich the
carbon between layers of Kevlar to offset the brittle nature of carbon in
thin laminates.

As Hank Hays says, "Carbon is not all it is cracked up to be."  (Did I get
that right Hank?)

I recommend that the Kevlar laminates be BI-axial and that the carbon be
Uni. directional and run diagonally across the hull. This provides a good
blend of stiffness and impact resistance.  I have seen recent reports
condemning the fabrics with mixed fiber (carbon/Kevlar and glass/carbon).
Apparently stresses build up causing breakage along the carbon strands. I
do not know why this occurs but have seen examples so my conservative
nature leans towards avoiding these materials.

Cheers,
John Winters
Redwing Designs
Specialists in Human Powered Watercraft
http://home.ican.net/~735769/

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From: <HTERVORT_at_aol.com>
subject: Re: [Paddlewise] Slamming
Date: Sun, 14 Mar 1999 23:41:39 EST
<< Is Kevlar "stronger" than fiberglass or is it just lighter?
  >>

Kevlar fiber and cloth has superior tensile and tear strength to glass fiber
and cloth.  I think the real question is:  " Are Kevlar composite boats
"stronger" than fiberglass composite boats?"

I believe the (long) answer is that, for the same weight boat, the Kevlar
composite boat (usually a combination of kevlar and glass-fiber materials in
polyester or vinylester resins) will be stronger and far less likely to suffer
catastrophic failures (like the whole bow breaking off, versus just cracking)
than the same model made solely with fiberglass.

However, most manufacturers utilize the superior tensile strength of the
Kevlar to make boats which are lighter but of approximately the same strength
as their glass models, thus making them far more desirable to the customer who
tends to worry a lot about weight.

If I were ordering my "perfect" boat, I would request a heavier "expedition"
Kevlar lay-up.  What I would be looking for is a boat which is just as stiff,
and considerably stronger than the (all) glass version, while saving (at most)
3 to 5 pounds (rather than the 10 to 20-pound savings of most Kevlar lay-ups).
Steph Dutton had a special Kevlar boat made for his winter-time paddle of the
Oregon coast, which weighed something like 15-20 pounds heavier than the stock
glass model.  It took tremendous abuse on that trip, then was later loaned to
some no-mere-mortal who ran the Grand Canyon (yes, Class 5 sections and all)
with its 16-1/2 foot hull loaded with full expedition camp gear.  The boat
looked beat, but unbroken.  I wouldn't doubt you could drive a 16-wheeler over
the thing.

The reason people worry about spider cracking of the gel coat on Kevlar boats
is because the lighter Kevlar boat is usually more flexible (while not
necessarily weaker) than the standard-weight glass version.  This is not a big
problem for people who exercise a lot of care with their boats, but may give
some grief to the more hell-bent adventurous, those prone to sit heavily on
their decks, and to outfitters who must allow their boats to be used by the
careless or uninitiated.  Curved sections are stronger and more rigid than
flat sections, so boats which have vaulted decks have fewer problems with gel
coat cracking than those with flat decks, unless the manufacturer takes
measures to stiffen the flat sections (coremat, carbon fiber, or others as
mentioned by John Winters).

Harold 
So. Cal.

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From: Hank Hays <lhays_at_canby.com>
subject: Re: [Paddlewise] Slamming
Date: Mon, 15 Mar 1999 20:59:46 -0800
Original question:
>>Is Kevlar "stronger" than fiberglass or is it just lighter?
>>
Harold wrote:
>Kevlar fiber and cloth has superior tensile and tear strength to glass fiber
>and cloth.  I think the real question is:  " Are Kevlar composite boats
>"stronger" than fiberglass composite boats?"

Hank?
Agreed, but it's a slippery question because of different kinds of
strengths.  Strong isn't necessarily the same as strong.  Materials break
in many different ways.  Tensile strength (pulling apart), compressive
strength (pushing together), shear strength (cutting as with scissors),
interlaminar shear (will the plys separate easily - the boat "come
unglued"), plus a lot of slow acting factors like durability (slow wearing
away), abrasion resistance (related to the previous), weatherability
(environment, usually water, affecting the material), there are many
more...   Keep it simple --  Kevlar just doesn't reinforce exactly like
glass.  

Harold:
>I believe the (long) answer is that, for the same weight boat, the Kevlar
>composite boat (usually a combination of kevlar and glass-fiber materials in
>polyester or vinylester resins) will be stronger and far less likely to
suffer
>catastrophic failures (like the whole bow breaking off, versus just cracking)
>than the same model made solely with fiberglass.

Hank:
Agree, usually, but a combination of the two will be even better.  By the
way polyester doesn't stick very well to Kevlar.  Vinylester is better, but
epoxy is required to do a reasonable job in my opinion.  Not many boat
manufacturers must agree as few use epoxy.  In low stress situations,
vinylester and Kevlar together are probably fine.  I consider most sea
kayak applications as low stress, excepting those few instances of "abuse"
and "slamming" I keep seeing in the subject header above here (cringe,
cringe..).  I don't consider vinylester and Kevlar as good for whitewater
boats, but it probably is used in some.  

Harold:
>However, most manufacturers utilize the superior tensile strength of the
>Kevlar to make boats which are lighter but of approximately the same strength
>as their glass models, thus making them far more desirable to the customer
who
>tends to worry a lot about weight.

Hank:
And they can usually get away with it because most sea kayakers are
relatively easy on their boats.  

Harold:
>If I were ordering my "perfect" boat, I would request a heavier "expedition"
>Kevlar lay-up.  

Hank:
I've done exactly that for the last couple composite boats I bought.
Despite all this composite construction advice I'm spewing, I haven't built
a boat for me for several years now.  Plan on doing it, just haven't gotten
around to it yet.  These people keep ordering paddles....

Harold:
>some no-mere-mortal who ran the Grand Canyon (yes, Class 5 sections and all)

Hank:
The Grand Canyon is very easy on boats.  If you hit a rock while in the
Grand Canyon it's because you tried to (or don't belong there in the first
place?).  People ran Klepper folders down that stretch back in the 60s
without any equipment problems.  

Harold:
>The reason people worry about spider cracking of the gel coat on Kevlar boats
>is because the lighter Kevlar boat is usually more flexible (while not
>necessarily weaker) than the standard-weight glass version.  

Hank:
Yup.  Exactly right.  

Hank Hays
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From: <wanewman_at_uswest.net>
subject: Re: [Paddlewise] Slamming
Date: Tue, 16 Mar 1999 00:49:25 -0600
I think the issue with some paddlers doubting the " strength " of kevlar is
related to the specific property of hull stiffness.  Kevlar FRP layups have
tremendous tensile strength for their weight and are superior to other materials
for tensile strength such as polyolefins, marine plywood, E-glass FRP layups etc.
However since it is so strong per weight and volume the layups often have much
thinner hull than the other materials.  I am sure some mechanical engineer will
call me on the equation, but I recall that the stiffness of a sheet of material
(its resistance to deflection or bending) varys by the square of the thickness of
that sheet.  Even a slight increase in hull thickness pays big dividends in
stiffness and resistance to denting or " oil canning ".  My father is the plastics
expert who has designed everything from FRP car bodies to a proposed design for
FRP tank treads, and could pass along all of the proper tech-talk and equations to
anyone who really wants to immerse themselves in the technical aspects of FRP
composites.

 If you are putting a load on a sheet of material you may be much better off
stiffness wise with a a weaker material but a greater thickness.  An inch thick
hunk of styrofoam is much thicker than a thin sheet of Kelvar FRP for example.  A
thicker hull such as a ceder strip or marine plywood is going to be much more
resistant to denting or bending in most cases than a thin Kevlar layup.  Some race
designs use a PVC foam core or other filler material between Kevlar FRP skins or
other structure modifications such as ribs to give the layup thickness and much
greater stiffness.  This is unfortuantely ususally very expensive.  My experience
with a lot of thin Kevlar layups is they bend, and dent but they don't break.  You
may crack the resin, but it is damned hard to tear or break apart a kevlar layup
boat.  However if your kayak has a big dent in it or folds in half still in one
piece you might be wishing you had traded some of that tensile strength for a more
rigid hull mad from a " weaker " material.

Hank Hays wrote:

> Original question:
> >>Is Kevlar "stronger" than fiberglass or is it just lighter?
> >>
> Harold wrote:
> >Kevlar fiber and cloth has superior tensile and tear strength to glass fiber
> >and cloth.  I think the real question is:  " Are Kevlar composite boats
> >"stronger" than fiberglass composite boats?"
>
> Hank?
> Agreed, but it's a slippery question because of different kinds of
> strengths.  Strong isn't necessarily the same as strong.  Materials break
> in many different ways.  Tensile strength (pulling apart), compressive
> strength (pushing together), shear strength (cutting as with scissors),
> interlaminar shear (will the plys separate easily - the boat "come
> unglued"), plus a lot of slow acting factors like durability (slow wearing
> away), abrasion resistance (related to the previous), weatherability
> (environment, usually water, affecting the material), there are many
> more...   Keep it simple --  Kevlar just doesn't reinforce exactly like
> glass.
>
> Harold:
> >I believe the (long) answer is that, for the same weight boat, the Kevlar
> >composite boat (usually a combination of kevlar and glass-fiber materials in
> >polyester or vinylester resins) will be stronger and far less likely to
> suffer
> >catastrophic failures (like the whole bow breaking off, versus just cracking)
> >than the same model made solely with fiberglass.
>
> Hank:
> Agree, usually, but a combination of the two will be even better.  By the
> way polyester doesn't stick very well to Kevlar.  Vinylester is better, but
> epoxy is required to do a reasonable job in my opinion.  Not many boat
> manufacturers must agree as few use epoxy.  In low stress situations,
> vinylester and Kevlar together are probably fine.  I consider most sea
> kayak applications as low stress, excepting those few instances of "abuse"
> and "slamming" I keep seeing in the subject header above here (cringe,
> cringe..).  I don't consider vinylester and Kevlar as good for whitewater
> boats, but it probably is used in some.
>
> Harold:
> >However, most manufacturers utilize the superior tensile strength of the
> >Kevlar to make boats which are lighter but of approximately the same strength
> >as their glass models, thus making them far more desirable to the customer
> who
> >tends to worry a lot about weight.
>
> Hank:
> And they can usually get away with it because most sea kayakers are
> relatively easy on their boats.
>
> Harold:
> >If I were ordering my "perfect" boat, I would request a heavier "expedition"
> >Kevlar lay-up.
>
> Hank:
> I've done exactly that for the last couple composite boats I bought.
> Despite all this composite construction advice I'm spewing, I haven't built
> a boat for me for several years now.  Plan on doing it, just haven't gotten
> around to it yet.  These people keep ordering paddles....
>
> Harold:
> >some no-mere-mortal who ran the Grand Canyon (yes, Class 5 sections and all)
>
> Hank:
> The Grand Canyon is very easy on boats.  If you hit a rock while in the
> Grand Canyon it's because you tried to (or don't belong there in the first
> place?).  People ran Klepper folders down that stretch back in the 60s
> without any equipment problems.
>
> Harold:
> >The reason people worry about spider cracking of the gel coat on Kevlar boats
> >is because the lighter Kevlar boat is usually more flexible (while not
> >necessarily weaker) than the standard-weight glass version.
>
> Hank:
> Yup.  Exactly right.
>
> Hank Hays
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From: David Carlson <qajaq_at_nwlink.com>
subject: Re: [Paddlewise] Slamming
Date: Tue, 16 Mar 1999 18:48:16 -0800
You were right, this mechanical engineer will call you on it.
Bending stiffness is proportional to thickness cubed (even more
sensitive to thickness than you thought).

Cheers,

Dave Carlson

wanewman_at_uswest.net wrote:
> 
<snip>
> thinner hull than the other materials.  I am sure some mechanical engineer will
> call me on the equation, but I recall that the stiffness of a sheet of material
> (its resistance to deflection or bending) varys by the square of the thickness of
> that sheet.  Even a slight increase in hull thickness pays big dividends in
> stiffness and resistance to denting or " oil canning ".  My father is the plastics
> expert who has designed everything from FRP car bodies to a proposed design for
> FRP tank treads, and could pass along all of the proper tech-talk and equations to
> anyone who really wants to immerse themselves in the technical aspects of FRP
> composites.
> 
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From: Bob Apter <bapter_at_sos.net>
subject: Re: [Paddlewise] Slamming
Date: Mon, 15 Mar 1999 10:44:22 -0800
-----Original Message-----
From: HTERVORT_at_aol.com <HTERVORT_at_aol.com>
To: 735769_at_ican.net <735769_at_ican.net>; paddlewise_at_lists.intelenet.net
<paddlewise_at_lists.intelenet.net>
Date: Sunday, March 14, 1999 8:43 PM
Subject: Re: [Paddlewise] Slamming


><< Is Kevlar "stronger" than fiberglass or is it just lighter?
>  >>
>
I have a Kevlar X-Par Missile, a racing kayak that is 23 feet long, has an
18" beam and a large cockpit.  The size of the cockpit may compromize its
structural strength.  I once wet-exited after missing a roll.  After getting
back to the beach, in frustration I lifted one end of the boat to drain it
while it still had considerable water inside.  In doing so I cracked the
hull in the cockpit section.  It has since been repaired and is stronger now
than as originally built, but I am concerned that if I were to have to wet
exit and re-enter in big seas with a flooded boat, the boat could break up.

Any comments?  Has anyone ever heard of a kayak breaking up in seas?

Bob Apter

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From: Hank Hays <lhays_at_canby.com>
subject: Re: [Paddlewise] Slamming
Date: Mon, 15 Mar 1999 21:03:33 -0800
Bob,

>Any comments?  Has anyone ever heard of a kayak breaking up in seas?

I have not, but it would surprise me if it hasn't.  Doesn't happen in
whitewater, even to glass boats, it's the rocks that do the damage.  I've
paddled fairly light composite open canoes (with airbags) down the Grand
Canyon twice now without any problems.  I'd expect more damage when a sea
kayak hits the beach (as per these "abuse" and "slamming" threads), but a
really light racing boat like you are using isn't built for much except
flatwater racing (impact? what's impact?) and impact is a no, no.  Big
waves with water already in the boat could do it.  Probably wouldn't hurt a
boat designed for whitewater much unless it was continually pounded for
weeks and weeks.  
Hank Hays
Lightning Paddles
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From: Bruce Winterbon <bwinterb_at_mail.magma.ca>
subject: Re: [Paddlewise] Slamming
Date: Mon, 15 Mar 1999 18:38:58 -0500
John Winters wrote:
[snip]
>
>I once watched Darryl Lideigh of Mohawk canoes pound on one of his chopped
>fiberglass canoes with a hammer. The boat stood up just fine. Not sure what
>that proved. Real life proves more.
>
My neighbour's rotomolded whitewater kayak was riding on someone else's car
when the car was rolled. After the car was righted, and the pillars in the
boat were pushed back into place, there were no scratches that he was sure
were new.
Some time later, with the same boat, he got stuck in a hole. He came out on
a rope, and the boat flushed out later: at least one good big new scratch on
the boat.
But a few years earlier, in a glass boat, he was pinned on another river.
Two of us got him out, but it took a while. I have never seen anyone so
happy to see his boat break in half. It is for this reason that careful
makers of glass whitewater boats made the cockpit region the weakest part of
the boat.

And what does that prove? Don't know, but here are some possibilities:
1) rotomolded boats are incredibly tough.
2) moving water can break anything
3) stronger need not be better. 
4) with age and experience you can amass a stock of irrelevant anecdotes for
any occasion. (So _that's_ why we do these things!)

Regards
Bruce

Bruce Winterbon
bwinterb_at_magma.ca
http://magma.ca:80/~bwinterb

The government measures the health of the economy by how
fast the rich get richer.

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From: <HTERVORT_at_aol.com>
subject: Re: [Paddlewise] Slamming
Date: Tue, 16 Mar 1999 02:29:45 EST
Bob,

Hank said it best.

The X-Par is an extremely light boat.  A friend of mine always stands
astraddle his whenever its not tied down to his roof rack because it will blow
away in the slightest puff of wind.  Its designed for speeeed and not for
heavy conditions.  I think I'd be concerned if I were in big seas, but then
I'm a professional worrywart.

Harold
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