[Paddlewise] Mystery of why good hatches go bad solved?

Matt Broze wrote:
> I don't know why VCP hatches don't last longer but I suspect it might be
> that the rubber is actually a foam so the air in it will allow it to float
> (even with the stainless steel ring around it. (BTW Doug--putting a little
> bend in the steel ring right next to the white clip attachment will make the
> clip work again.) A solid rubber cover might last longer but if it ends up
> at the bottom of the ocean
SNIPPED
> Upon reading of the short life among those who were using 303 I had to
> wonder if maybe 303 isn't the best thing for a VCP hatch. Anyone out there
> use 303 on both sides and have a 3 year or less life on a VCP lid?

I have an hypothesis on why the underside, in defiance of the logic that
the upperside would sustain the most exposure and UV damage, is reported
to be the side with the greatest tendency to show cracks according to
paddlers reporting on this issue.  It has to do with the nature of the
flexing of the lid and how the two different planes (topside and bottom
side) are affected by the action of placing the lid over the hatch hole.

The way the hatch is placed over the hole goes something like this.  You
first slip the lid's rim over a portion of the hole's lip, say a third
or so of the circumferance of the lid.  Next, and this is where the
deterioration effect may lie, you bend the rest of the lid upward to get
it over the rest of the hole's lip before than pushing the lid down.

Two different planes are involved here, the bottom and top plane.  If
the lid is a foam as Matt believes it is (good supposition since the lid
will float) then the lid basically has two hardened film surfaces with
aerated material in between (in a sense it resembles the structure of
the material in a cardboard box, i.e. hardened surfaces with a
corrugated core).  As you go through the action of flexing the lid to
fit around the hole's lip, the lifting of one end of the lid puts
greater splitting stresses on the underside surface than on the
upperside surface.  The underside surface is being stretched and bent
with a force tending to part its material, whereas the upper surface is
being bent inward.  This latter crimping action of the upperside will
eventually do in its surface but not as fast as the splitting action
that the underside is going through.

So that is why you may tend to see more cracking on the underside than
on the upperside as people have been reporting.  It is probably not
related to UV damage but to the stresses on the material.

You can test this hypothesis (which I don't feel like doing right now;
remember it ain't my problem: I don't have no stinking hatches :-)) by
cutting off the lid of a cardboard box and cutting a circular piece
about the diameter of a hatch.  Mark one side with a felt pen "T" for
top (i.e. don't use a sharpened pencil which will slightly score the
surface).  Now start bending the cardboard circular piece the way you
would for getting a hatch on and off, i.e. lifting repeatedly about one
half or one third of the side marked "T".  You will likely start seeing
the non "T" side developing cracks.  The cardboard test is a bit unfair
in that the corrugation material inbetween is corrugated in a parallel
pattern whereas the aerated middle material of the Valley hatch is
unidirectional with no set pattern.

Whether this hypothesis holds true or not there is a bigger safety issue
and it is this:

--Valley hatches are on fiberglass boats, mainly if not exclusively, and
cover hatch holes of glassed in watertight compartments.

--Paddlers of such better kayaks, in general, are not so inclined to use
air flotation in those compartments because of the pretty solid
bulkheads backing them.

--No where is it written in company literature that comes with such
kayaks (am I mistakened on this?) that the hatches are susceptible to
cracking over x years of use and should be regularly checked.

--Many paddlers of such kayaks are non-suspecting (until this discussion
on Paddlewise has helped draw attention to it) of the potential problem.
So there are some paddlers out there who may have a serious breach of
their watertight compartments were the hatches to fail in increments or
catastrophically.

This suggests that it is worthwhile reminding people who you see with
such hatches to check them out.

That is the nice thing about PaddleWise: it acts as wide network to help
individuals see that something that is happening to them and their boats
may not be an aberration.  Also discussion may even lead to some
solutions suggested by others on the listserve.  We saw this earlier
with VHF radios and relative waterproofness; the same with GPS is very
good discussions and give and take.  Lots of other areas have been
covered wisely here as well.

ralph diaz  
-- 
-----------------------------------------------------------------------
Ralph Diaz . . . Folding Kayaker newsletter
PO Box 0754, New York, NY 10024
Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com
"Where's your sea kayak?"----"It's in the bag."
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