Red wrote:
As I understad it, Kevlar is not only difficult to get a good bond with,
its not all that great for collision protection as it is for puncture
protection.


"Kevlar" as applied in structural composites (ie boat building) is
cloth made of fibers, same as fibgerglass is cloth made of glass
fibers. No magic here.

BTW it may be interesting to note the structural properties of
fiberglass, some other composites, and steel. It is relatively easy to
build a composite that is as strong as steel. It's also easier to
scale the structural properties to the size of the vessel. This latter
property is why steel doesn't make good small boats.


Besides, your answer doesn't address what I was asking - something that
can be applied on an older existing hull. I believe Kevlar would not
bond well enough on old polyester to make this practical anyway. Is this
correct?


No. Kevlar bonds just fine to existing hulls. I know of several boats
that have had this done. It would be better to apply it to the inside
of the the hull, where impacts put the laminate in tension, rather
than the outside (compression) face. However this is not always
practical, and it certainly helps the impact resistance of
"conventional fiberglass" to have a layer of Kevlar cloth on the
outside. A big problem to beware of is that Kevlar can't be faired...
sanding into the cloth leaves frizzies that will NOT lay down no
matter how much resin or paint you try to cover it with. So any
attempt to armor an older hull should have a thin layer of matt or
finishing cloth sandwiched over the Kevlar.

It would also be a very good idea to add positive flotation.

Fresh Breezes- Doug King

Doug King replied:
No. Kevlar bonds just fine to existing hulls. I know of several boats
that have had this done. It would be better to apply it to the inside
of the the hull, where impacts put the laminate in tension, rather
than the outside (compression) face. However this is not always
practical, and it certainly helps the impact resistance of
"conventional fiberglass" to have a layer of Kevlar cloth on the
outside. A big problem to beware of is that Kevlar can't be faired...
sanding into the cloth leaves frizzies that will NOT lay down no
matter how much resin or paint you try to cover it with. So any
attempt to armor an older hull should have a thin layer of matt or
finishing cloth sandwiched over the Kevlar.

It would also be a very good idea to add positive flotation.

Fresh Breezes- Doug King

I hear ya on the flotation!

The reason I asked is that I read an article somewhere way back on some
boatbuilding site that kevlar wouldn't bond adequately to old poly
resin. I'm curious though, why would it be better for the kevlar to be
on the inside? Wouldn't that make it less effective in a collision due
to the layer being in tension so it wants to seperate? I would have
thought that being on the outside would be better to provide a barrier
to the forced entry. Could you explain further? Thanks

Red

On Mar 10, 3:30 am, wrote:
... Kevlar bonds just fine to existing hulls. I know of several boats
that have had this done. It would be better to apply it to the inside
of the the hull, where impacts put the laminate in tension, rather
than the outside (compression) face. ...

Amen. But, having been tangentially involved in a completely
disastrous attempt to bond Kevlar (tm) fabric to PVC foam with epoxy I
strongly advise getting advise from the fabric provider before
bonding. A Method that worked very well with both epoxy and polyester
with stitched glass didn't fly with Kevlar (literally as the structure
was a wing for an ultra-lite). And, yeah, you're right, the stuff
goes all fuzzy if you look at it funny and it kills scissors. Carbon
is less of a pain to work with but you can't use it to armor existing
hulls.

-- Tom.

On Mar 6, 4:11*pm, wrote:
On Thu, 06 Mar 2008 00:01:18 -0800, ray lunder
wrote:

Anyone owned a steel hulled sailboat in the 40 foot range and have
some advice on what to look for when buying one? Thanks as always.

Make sure the steering quadrant can't fail and sink the boat by poking
holes in the hull.

For that size and weight of boat; lots of money! Health and fitness
and a certain amount of strength. Also probably some crew, unless it
is fitted with fairly elaborate gear.
Good luck.