Thanks, Roland, for the commments. The only info I have about the
Monokote is Platt's experiments where the stuff cracked quite badly
when left in the sun for awhile. Both my other sof and fiberglassed
strippers also claimed poor uv resistance but I coated them with three
coats of spar varnish with uv inhibitors and they have held up well. I
know that people have done experiments with the fiberglassed boats and
have said that at least three coats of marine spar varnish has
protected them very well no degradation. Less than three coats has
left them susceptible.
PS. A really stupid thing I did: I damaged a sof kayak--it flew off
the top of the car--racks and all (that's another story)--and I
repaired it. The skin was getting quite dirty and yucky so I decided
to paint it. I forgot about the spar varnish on it and painted it
latex enamel. Huge Mistake. Peeling off everywhere. The one I'm
building now is it's replacement. Between the repair work and painting
the old one isn't worth re-skinning.
> Well, UV susceptibility is cited as a weakness for the Dacron, as
> well. OTOH, Dacron is the most common sailboat sail material, and
> also used in wing and fuselage coverings for experimental aircraft
> (apparently, this is what inspired Platt to try it on boats), while
> Mylar and variants (Monokote, Coverite, etc.) are extensively used in
> covering RC airplanes and in windsurfer sails, all activities with a
> _lot_ of sun exposure, so there must be some qualifications to how UV
> sensitive these materials are.
> For example, I have read many accounts of sailboat circumnavigation,
> solo or by couples, in < 40' craft. I can't imagine such a craft
> carrying more than two full sets of
sails, and I can't imagine the
> crew running a major risk of sails failing from UV degradation before
> the voyage is completed. Such voyages commonly take six months or
> What I hope to find out is approximately how many hours of full sun
> exposure equals deterioration beyond safe use for various materials.
> That still will likely not account for latitude, time of year, etc.,
> but should at least provide a basis for materials planning and further
> investigation, post-build.
> There is also the issue of UV-inhibitors and protectors (e.g, Formula
> 303). I'm somewhat skeptical of the protectant claims, based
> on a Car and Driver study of auto waxes and poly finishes several
> years ago that concluded that the amount of UV protection was directly
> proportional to the thickness of the coating, irrespective of the
> coating chemistry.
> Anyway, UV issues re GA boats seems to be an issue that merits further
> discussion and study.