Re: [Paddlewise] VCP Hatch Deterioration - another hypothesis

Ralph wrote:
> 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.
<<snip the rest>>
>
This certainly sounds plausible, but consider:
IF the hatches are made of natural rubber, a contributing factor may be the
physical properties of the rubber itself.  Caveats: I don't know if VCP
hatches are made of natural rubber (rather than some other type of
elastomer) and I don't have VCP hatches on my boat (so I have no personal
experience with cracking VCP hatch covers) - but the chemist in me has an
idea, supported by a bit of evidence.

Encarta (http://encarta.msn.com/find/concise.asp?mod=1&ti=01307000&page=2)
defines rubber's physical properties this way:
"Pure crude rubber is a white or colorless hydrocarbon. The simplest unit of
rubber is isoprene, which has the chemical formula C5H8. At the temperature
of liquid air, which is about -195° C (about -319° F), crude rubber is a
hard, transparent solid; from 0° to 10° C (32° to 50° F) it is brittle and
opaque, and above 20° C (68° F) it becomes soft, resilient, and translucent.
When rubber is mechanically kneaded, or is heated above 50° C (122° F), it
becomes plastic and sticky; above 200° C (392° F) it decomposes.  Crude
rubber is insoluble in water, alkali, and weak acid; it is soluble in
benzene, gasoline, chlorinated hydrocarbons, and carbon disulfide. It is
oxidized readily by chemical oxidizing agents, and slowly by atmospheric
oxygen."

The key here is the last sentence, which states that natural rubber has poor
solvent/chemical  resistance.  I'm suggesting that the chemical vapors from
the *inside* of the boat are chemically weakening the rubber so that it may
be more prone to cracking.

Most of the respondents to this thread have stated that the cracking occurs
on the *inside* of the hatch cover, which cannot be caused by UV radiation
as UV cannot penetrate through an opaque hatch cover.  Physical flexing is
certainly a possiblilty, but one of natural rubber's *best* properties is
its elasticity and resilience, which would indicate that repeated flexure
should not be a problem.  These two links compare the properties of natural
rubber to those of other elastomers:
http://www.sasindustries.com/serv01.htm
http://www.tamparubber.com/mainprop.htm

I pose these questions to those who have reported cracks in their hatch
covers:
1.  Do you routinely keep your hatch covers installed on the hatches?
2.  If so, do you smell a resin/chemical smell inside your hatch when you
first remove the hatch cover?
3.  Is your boat relatively new?

If the answer to these questions is yes, I'm suggesting that the chemical
vapors that are generated by the resin and/or the catalyst used to make the
boat are either chemically degrading the rubber to the point where it
cracks, or are chemically degrading the rubber to the point where the
flexural stresses as described by Ralph can cause the cracking of the inside
of the hatch covers.  The resins used in boatbuilding achieve much of their
final strength quickly, but take a *long* time to achieve full and
final cure - and generate chemical vapors in this slow curing process.

My supporting evidence?
Jack Martin wrote:
> Okay, MTBF on VCP hatches appears to be a couple or three years for those
> who have responded.  Is there anybody else out there who has gotten a lot
> of years out of their hatches?  Am I it?
>
but in his prior email, he had written:
> I do loosen them and leave them over but not attached to the flanges
>

Maybe the reason that Jack gets the additional life out of his hatch covers
is the simple fact that he does not leave them attached to the hatches,
thereby letting any accumulated chemical vapors inside the boat dissipate.
And I'll bet that since he lets the inside of his hatches breathe, he also
doesn't have a strong (or any?) resin smell inside his hatches (though older
boats will have less of a resin smell to them).

If any of this *might* be true, then the simple solution would be to store
one's boat with the VCP hatch covers OFF the hatches - especially when the
boat is new.

Erik Sprenne
a Great Lakes paddler


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