Re: [Paddlewise] Durability

Peter Treby wrote:

>  I haven't noticed any objective measurements of boat strength
> claimed by manufacturers. How would strength be measured? Chain the boat from
> both ends and drive a truck over? I wonder if any non-destructive testing could
> be devised. Otherwise, all the boat buyer has to go on is anecdotal evidence
> from paddlers, for instance via this list, or self serving claims by
> manufacturers. Does anyone know of objective strength measurement for kayaks?

We could devise quite a few objective strength measurement, but getting folks
to agree on which to use and how relevant they are is another story.  I'd like to
know what parameters are used by designers.  For large ships, first order
calculations can be done by assuming the ship is suspended by the ends on
its bow and stern waves.  Things then get complicated real fast.

In general, non-destructive tests will indicate the structural integrity, but not the
limiting strength.  (I was an non-destructive testing technician when a university
student.)  Stiffness can be measured non-destructively.

I would be interested in a few test results for comparisons - but these are destructive:

1 - Flexure of the overall craft loaded at its centre and supported at the ends (sagging failure),
2 - Flexure of the overall craft loaded at its ends and supported at the middle (hogging failure).

These would indicate the strength of the kayak as it is supported by waves at its ends or
by one wave crest at the middle.  Basically we'd be testing both the deck and hull for
behavior under both tension and compression.  Relevant loading patterns are up for
discussion.  Should a day boat be subject to the same loading as a long distance touring
boat (ie. load in the middle [paddler] vs load distributed [paddler + gear])?  How do we
support the ends - small area or large?  Support the middle?

3 - Puncture of the hull from the bottom and from the side.
4 - Puncture of the deck from the top.

The hull has to deal with rocks, floating objects etc.  The deck has to deal with the paddler,
rescue techniques, deck mounted gear (eg. towing rigs) etc.  Should the puncture test be
static (press slowly to failure) or dynamic (whack it with specified energy levels to failure)?
What should the area of contact be and how rigid should the impactor be?  What shape
should it be?

There are standardized testing techniques in other areas of engineering, so this has been
done.  The debate is about how to standardize.  The problem for the consumer is how to
compare the results for the purposes for which they intend to use the kayak.

If folks are keen, this could probably generate as much debate as feathering or rudders.

Mike

***************************************************************************
PaddleWise Paddling Mailing List - All postings copyright the author and not
to be reproduced outside PaddleWise without author's permission
Submissions:     paddlewise_at_lists.intelenet.net
Subscriptions:   paddlewise-request_at_lists.intelenet.net
Website:         http://www.paddlewise.net/
***************************************************************************