Matt:
Some figures taken from West Epoxy web site where they did tests on bonding
strength of epoxy and polyester.
Tensile strength of original glass 26,198 PSI
Tensile strength of poly repair 18,460 PSI
Tensile of epoxy repair 21,404 PSI
Therefore polyester has a strength 13% less than epoxy at a cost of about
500% more.

"Matt Colie" wrote in message
...
John,

Any part, piece -whatever of any racing yacht can fail at any time, I
mentioned "Tomahawk" because I knew some of the cast involved and it was a
polyester bond that failed in this case and caused the loss of the vessel.

The way many boats are built today anything can fall off.

I agree that there is no substitute for proper practice.

My problem with polyester is simple, the bond strength is poor. If you
can do it all as a wet assembly, that is fine, but if you need to put
pieces together - polyester can be problems. I have done whole boats with
poly and vinylester (which is another animal). I completely agree that it
has its place. Most of them are in a mold.

See the beginning paragraph 13% difference.

If a guy is going to work under less than ideal conditions and do small
patches (less than a mold section), I always that they look at the
additional cost of epoxy. If you could get p or vest resin that had nice
little measuring pumps and was as well behaved, I still would be hard
pressed to advise it for repairs.

Polyester isn't that fussy but I use a Nalge dispenser and never had a
problem.


At the prices I pay 5 gallons (the smallest we buy) of poly is about
85$us, vinyl is about 140$us and 250$us for gallon mix - includes harder
of epoxy. The way any job works, labor is the big cost and the labor to
use gallons of resin is a big number.

The only problem with epoxy for repairs that require cosmetic surfacing is
taht you have to do a intermediate coat of vinyl to bond the polyester
gelcoat to the epoxy. Gelcoat will just fall right out of an epoxy
patch - given half a chance - it will has been know to do the same to a
poly repair but vinylester is good enough to bond the two.

And - when it come to the failures of super-lights - I don't even count
them as real. Like the ICAA boat that folded and sank off San Diego.
There is a reason why the shipwrights that I knew as a child worked the
way that they did. I have come to understand that all the wouldful new
analysis stuff like FEA, CFD and such are nice, but the people that have
been out there better not use it to determine what the sea can do.

Matt Colie

My main problem with epoxy is the people who think it's the holy grail,
I think anyone who
recommends epoxy to repair a deck on a 25 year old 20 foot boat has either
too much money or has been reading too many newsgroups.
I would think that the boat that started this discussion could be repaired
at minimum cost and be as strong as the good side of the deck. No more is
needed.
John


John M wrote:
Matt:
Actually I don't do repairs on cars.
You mention Tomahawk and her "polyester patch job" how about the other
five boats that lost their masts or the eight that were damaged or for
that matter the 96 that dropped out. All polyester patches?
There are many boats built down to a price that will have parts falling
off. But think off all the plain old polyester and glass boats that have
been around the world with little or no problems.
Which brings to mind a British catamaran whose name escapes me at
present, that was built for a round the world record attempt in 1999 or
2000. Built of prepreg epoxy, carbon fiber all the latest high tech. On
its first test run in weather that wasn't to bad its bows fell off. I
won't blame the epoxy or carbon fiber.
My point is epoxy and polyester have their place but nothing replaces
proper building practices.
With prices of epoxy at $74 a gallon and polyester at $105 for 5 gallons
it's hard to believe there is only a $200 difference in a $5000 job.
John



"Matt Colie" wrote in message
...

John,

Do you do body repairs with window screen and plastic filler?
You can make it look just as good as steel?

If you would go to sea in a boat patched with polyester, be my guest.
One of the famous ones in the book is "Tomahawk". She sank during a
Bayview Mackinac in the mid 80's. That was a polyester patch job.

A clients mast came down when it buckled at the spreaders because the
tabbing for the anchor for the lower came away from the hull side.

I helped recover a sloop that lost its steering because one of the
turning blocks came adrift.

Those last two were both bond failures of parts installed at teh builders
yard.

We are set up for resin infusion in several versions (skrimp, spike and
texp2) but none are well suited to most non-molded assemblies (that most
repairs).

Epoxy is used in repairs for two reasons, it has cohesive and adhesive
bond properties that far exceed that of poly or vinylesters. We
specialize in fixing things - once. Our clients only talk to us if they
want a first class job. We clould save the client 1or 200$ on a 5k$ job
by using cheap materials. We use only epoxy.

You can do what you want, but some of are not interested in doing it ont
he cheap - cheap is the price of low value.

Matt Colie

John M wrote:

Just wondering do you guys that use epoxy for everything also use
titanium for auto body repairs after all it's better than steel. It
seems rather silly to repair a polyester and glass boat which is old
with epoxy and the latest high tech fabrics. Why not try resin infusion
too
John
"Jim Conlin" wrote in message
...


I figure it'd be somewhat over $10/ft^2.
Core-cell $4-
maybe 4 laminations of:
12 oz. knitted Glass $10/yd = $.80/ft^2/ply
epoxy $70/gal = $.60/ft^2/ply

paint $1/ft^2
plus abrasives, peel ply, fillers, vacuum bag consumables


"DSK" wrote in message
. net...


Lew Hodgett wrote:


You haven't priced materials lately, have you?

Think OIL.


Actually, I have- am buying materials for a carbon fiber
rowing dinghy. But I think you grossly (very grossly)
overestimated the cost & amount of materials needed for
replacing core on a 20' deck.

It's not going to be free, that's not what I'm saying.

DSK