Re: [Paddlewise] Durability Testing

----- Original Message -----
From: <LedJube_at_aol.com>
To: <paddlewise_at_lists.intelenet.net>
Sent: Thursday, January 06, 2000 9:25 AM
Subject: [Paddlewise] Durability Testing (Seakayaker Mag are you listening?)


> ...
> The Tests (a work in progress) -- primarily fiberglass for now but tests
for
> plastic boats would also be required.
>
>     Resistance to "Oil Canning" is mainly a design issue more that a pure
> strength issue.  If a section of the boat can flex to absorb a force
without
> cracking or weakening then that would be great, but most times the flexing
> leads to stress or compression cracks. So we should test for not only "Oil
> canning" but also material fatigue from repetitive "Oil Canning" at
various
> temperatures.
>
>     Resistance to cracking of the hull and deck in areas likely to see
> compressive forces.  Situations like paddle float reentry's, X rescues,
> sitting on the deck or sitting on the hull with the boat upside down.
>
> Impact Resistance
>     Dropping the boat as if it fell off the rack.  Drop various paddling
> related objects onto the deck.  Hitting submerged rocks.  Whack the boat
into
> something while being carried.
>
> Abrasion resistance
>     Run the boats up onto and /or drag them over rocky shores
>
> Penetration Resistance, Shear Strength
>     I'm not sure how to define these or how valuable they might be.
>
> Other test that might benefit from more scientific testing
> Weathercocking, tracking, maneuverability (even keel and tilted)
>     Certainly not strength related but may use much of the same equipment
as
> other "strength related" test.
>
>     Certainly the list could go on and on.  Please add as you see fit.
I'm
> willing, at the mere hint of interest by someone like Seakayaker Mag to
> compile your responses, poll the manufacturers and get this thing rolling.
>

Wow, this could get very expensive.  I think it would be very difficult to
get quantitatively useful results.  An important is the question what is
their durability and safety after experiencing these abuses.  To really
understand the durability of a boat you have to use _many_ copies of the
same boat and do _many_ tests like:

    - Drop a boat off the rack x times, then measure the force it takes to
snap the boat in half by folding it
    - Drop a boat off the rack x times, then measure the force it takes to
compromise the deck by dropping a load on it.
    - Drop a boat off the rack x times, then measure the force it takes to
flatten the boat to a height of 2" by applying pressure plate from the top
and bottom.
    - Drop a boat off the rack x times, then measure the force it take to
puncture the hull in
    - Drop a boat off the rack x times, then see if it oil cans
    - Drop a boat off the rack x times, then see if its deck-hull seam leaks
    - Drag the boat Y yards across rocky shores, then measure the force it
takes to snap the boat in half by folding it
    - Drag the boat Y yards across rocky shores, then measure the force it
takes to compromise the deck by dropping a load on it.
    - Drag the boat Y yards across rocky shores, then measure the force it
takes to flatten the boat to a height of 2" by applying pressure plate from
the top and bottom.
    - Drag the boat Y yards across rocky shores, then measure the force it
take to puncture the hull in
    - Drag the boat Y yards across rocky shores, then see if it oil cans
    - Drag the boat Y yards across rocky shores, then see if its deck-hull
seam leaks
    ...

And then you'd have to combine abuses in different combinations, then
determine the above outcomes.
And then you'd have to repeat it all many times to prove that a particular
failure wasn't the result of a boat that was contributing to the low end of
the mean-time-to-failure curve.

Very expensive.

If this sounds extreme, then consider the way that cars's safety is
determined (that is fully assembled cars).  You crash them and measure
forces exerted on things like test dummies.  Because of the cost, you're
probably only going to get three type of crashes tested: full-frontal (don't
search for this one :-), frontal-offset, and side-impact.  And that's if
you're lucky and somebody cared enough to test the car you want information
for.  An unfortunate problem with this testing method is that we never find
out if the results of the tests are repeatable.  It's not enough to do a
test just once.  You've got to repeat it (perferrably with a third party) to
know for sure.

What the auto industry/government does, however, to compensate for this
pragmatic inability to conduct real science in measuring the
safety/durability of a vehicle is to keep databases of incidents.  This
allows us to go back, in retrospect, and review the quality of a particular
model.  Unlike finance where past performance is not indicative of future
potential, these database can be representative of a manufacturer's quality.


So, what's my point?  I don't really know, I'm just blathering.  Maybe the
points are:
 - When (and if) anyone ever devises a durability test, be skeptical about
its ability to answer the question, "should I buy boat X instead of boat Y."
 - It can only be good for us (consumers) to get the word out about the
problems we encounter; this is much like the paddler safety incident
articles in Sea Kayaker and those in other magazines like Flying.  Smart
people learn from failures.

Evan


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