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

On 6 Jun 2003 at 2:46, jwd_at_acm.org wrote:

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

My passions only come from years of competition in other sports and 
seeing the futile waste in time and money on getting the "best" and 
lightest gear when the participant basically lacks skill, fitness 
etc.  While there are ways to make kayaks better, is it worth the 
price (extra maintenance, etc)?  

>   "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.

Be careful to keep strength and stiffness separate.  They are 
different properties and in some cases (like buckling) are completely 
independent.  He's talking about strength; I was only addressing 
stiffness.  (OT - what emissions are produced in the manufacture of 
polycarbonate?  He only looks at _his_ use of the final product! BTW, 
this is not to suggest that polycarbonate is bad, just to ask the 
question.)

> 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.

First comment on terminology: epoxy is rarely used in commercially 
produced kayaks.  Most manufacturers use a resin  (vinylester, 
polyester whatever) which is cheaper and does not have the same 
properties as epoxy.

Oilcanning will be reduced by increasing the layup thickness (and 
according to Nick, would be more weight efficient than using 
gelcoat).  Buckling failure would also be reduced.  

(BTW oilcanning is due to forces perpendicular, however, buckling is 
due to forces in the plane of the laminate.  Also you should say 
flexible not weak just to be clear.)

This brings up a point that hasn't been addressed.  If they order the 
kayak without gelcoat, what do they get?  Thicker laminate?  The same 
laminate?  Different laminate?  My comments assumed that they would 
get the same laminate without gelcoat.


> 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
> [...]
> 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).

These things are easy enough to look up and calculate.  However, it 
does beg the question - How much is enough?

> 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. 

I'd call that naïve.  I've seen enough frayed glass fibres on kayaks 
to know that's not necessarily true.

> 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.

Time trials don't need light weight.  Criteriums, with acceleration 
out of every corner would benefit from lighter weight.  This does 
remind me, though, of my cycling coach who was at least 20lb 
overweight and yet had a titanium chain on his bike!  His bike was 
three pounds lighter than mine, but I could beat him up any hill you 
could find!

Mike

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