Re: [Paddlewise] Spare the gelcoat -- pros & cons of skin-coat boats

[ You're obviously pretty passionate about this, so don't misconstrue my
  comments as argumentative. ]

On Fri, Jun 06, 2003 at 12:23:46AM -0400, Michael Daly wrote:

> On 5 Jun 2003 at 21:44, jwd_at_acm.org wrote:

>> Their justification was that gelcoat provides no structural benefit
>> to the boat, and going without it saves 5-8 lbs of essentially
>> useless weight.

> Not true.  The gelcoat increases the thickness of the hull and 
> provides for greater stiffness.  Without the gelcoat, you're more 
> likely to get oilcanning and possibly buckling at the limit of what 
> the kayak can handle. (Unless you beef up the fibre and resin, which 
> negates some or all of the weight saving.)

FWIW, here's a quote from Eddyline's website.  It matches nearly word
for word a phone conversation I had with Tom Derrer 2-3 years ago.

  "Gel coat adds color and UV protection, but it also adds extra
   weight, provides no strength to the laminate and contributes to
   atmospheric emissions."

So, he at least, thinks it adds no strength to the laminate.

Now, I don't necessarily agree.  Or, to be more precise, I would say
it doesn't necessarily add any **necessary** strength or stiffness to
the hull.

If you make the fiberglass/kevlar/carbon-fibre (w/ epoxy resin)
laminate sufficiently thick so as to provide the necessary hull
stiffness, can you still say you're more likely to get oil-canning or
buckling?  I would say that would only be the case if the laminate was
weak in the face of forces perpendicular to, or nearly so, the lay of
the fabric laminate.

As to the argument about beefing up the fibre and resin, I would have
to ask two questions.  1) Just how much beefing up is required, if
any, given the typical glass/kevlar build, to provide a sufficiently
robust hull for non-expedition use?  2) Even if you have to beef up
the glass/kevlar laminate, cay you really say that's a one-to-one
weight exchange with the gelcoat you're leaving off?  That would
require you know the comparative weights of the materials, and not
simply for a particular thickness, but for the thickness necessary to
give a certain amount of added "strength".  I don't know that
information.  Do you? (and no, I'm not being a wise-ass, just asking).

> The gelcoat also protects the resin and fibre from impact and
> abrasion.  With the gelcoat, you've got a sacrificial layer.
> Without the gelcoat, the damage is done to the resin and to the
> fibres directly.  I'd rather not see damage to the main structural
> element in the composite.

This essentially covers the question I asked the person.  The response
was that (and these boats don't get babied -- nor do they get tossed
about carelessly either) the damage done is to the outer layer of
epoxy and not to the fabric within.  And that damage is easily
repaired with a little clear epoxy.  I guess it boils down to whether
or not the epoxy on the outside of a skin-coat boat provides enough
"sacrificial layer" to withstand normal wear and tear.  And, when it
doesn't provide enough protection, if it isn't just as likely that the
gelcoat outer layer of a more typical hull wouldn't fail just as
easily, resulting in underlying fabric damage too.  Hell, I don't
know, that's why I'm asking.

> The only folks that see a real advantage in kayaks (or canoes) 
> without gelcoat are the racers.  They are willing to sacrifice the 
> gelcoat in order to save a few pounds.  The rest of us have little 
> need for dropping a few pounds from our kayaks.  

That may indeed be the case.  It certainly is for bikes (except for
those doing time trials, and then only if they're seriously up to the
task).  That's why I ride lugged steel frames and only use titanium
parts for personal amusement.

As to the weight issue with kayaks, that is another can a worms for
discussion.  An argument I've seen floating about in print and on the
web, and have heard from fellow kayakers, is that most boats will, if
you put them on the scale, weight a good bit more than the
manufacturer's stated weight (sometimes 8-12 lbs. on a claimed 40-50
lb. boat).  That isn't a trivial amount of weight, either on an
absolute basis, or as a percentage of total boat weight.  If it were
trivial, no one would knock Brit-boat builds for weighing in the 60+
lb. range.  An argument for dropping the gelcoat was, in this
conversation, that it certainly provided a way to get a boat that
weighs what the builder claims for the design.  Like I said, however,
quite another can of worms.  Maybe best left shut.

> Next time you see these kayaking friends, check to see if they are so 
> buff that they couldn't lose 10 lbs weight and be more fit!   Unless 
> they're national team calibre, their likely wasting time and money on 
> an ultralight boat.

While they don't kayak just to race, they do race when they can.  And
they tend to finish near the front of the pack.  I'm sure that's 90+%
fitness and skill though, and not the boat.  But they do have an even
lighter boat just for racing, they just don't always use it when they
race.

Thanks for the interesting reply Mike.

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