steel hulls?
 

Capt. John
Overall, maintenance is somewhat higher (your labor), but not a bad
trade off in terms of vessel strength. If crossing the pond and you
happen to bang into a semi-submerged cargo container, you may get a
dent in the steel. With fiberglass, you're boat is likely to take the
Davey Jones express to the bottom.


I wonder if there isn't a practical way to make the underwater section
of the bow/keel stronger on an existing fiberglass boat stronger/more
impact resistant. Surely someone has figured this out, no?

Red

steel hulls?
 

steel hulls?
 

I wonder if there isn't a practical way to make the underwater section
of the bow/keel stronger on an existing fiberglass boat stronger/more
impact resistant. Surely someone has figured this out, no?

Red

Salty:
Yes. It's often accomplished by the addition of a layer or two of
kevlar cloth during layup.

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.

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?

red

steel hulls?
 

On 2008-03-09 15:54:59 -0400, Red said:

I wonder if there isn't a practical way to make the underwater section
of the bow/keel stronger on an existing fiberglass boat stronger/more
impact resistant. Surely someone has figured this out, no?

Our designer made the first 5-7' of our 28' boat an isolated chamber.
We, or an errant hole in the bow, could fill that section up without
much compromising our sailing ability as it's disconnected from the
rest of the boat, buoyancy-wise.

As I review the boat's layup, we could take holes a bit further back
with little problem, though absolute safety would require our being
pretty much upright.

I should review my numbers in view of what I've learned since, but at
one time I calculated that if we got a BIG hole in the middle of the
boat, we'd likely not sink due to the massive isolated chambers in our
bow and stern. We might not float high, but we'd float.

In other words, I believe this problem has been figured out, but not by
assuming that we could make the holes impossible, which I feel highly
improbable, but by ensuring that the boat was properly buoyed when
holed.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

steel hulls?
 

Jere Lull wrote:

In other words, I believe this problem has been figured out, but not by
assuming that we could make the holes impossible, which I feel highly
improbable, but by ensuring that the boat was properly buoyed when holed.


That's because your boat was designed for Canadian sailing, so some
ice-breaking ability was a requisite.

Cheers
Marty

steel hulls? adding armor to FG hulls
 

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

steel hulls? adding armor to FG hulls
 

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

steel hulls? adding armor to FG hulls
 

Red wrote:
I hear ya on the flotation! :)


A lot of people seem to think it isn't practical. It would indeed mean
giving up some interior space, but IMHO many production boats could
have positive flotation installed and give up maybe 15~20% of useable
stowage. A lot of space could be used for flotation that is up in
tight angles & inaccessible spots.

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.

Can't think why that would be. It's just fancy cloth. More would
depend on the surface prep & type of 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


I can try. A laminated structure almost always fails in compression...
same as a mast BTW. As force applied increases and the structure
bends, at some point the strength of the bond between layers starts to
fail and the inner face of the bend, the skin that is under
compression, starts to buckle. This is where local tears in the skin
form. After this point failure occurs, the whole thing comes apart
like a zipper until the strain is relieved.

Kevlar is very very strong in tension, and along the tension face or
skin will distribute load over a much wider area than conventional
fiberglass cloth, thus avoiding critical point loading in the opposite
compression face.

OTOH if you're thinking of an object piercing the hull like an ice
pick, having the Kevlar layer on the outside might not make much
difference. In any event, having it on the outside is better than
nothing.

Fresh Breezes- Doug King

steel hulls? adding armor to FG hulls
 

OTOH if you're thinking of an object piercing the hull like an ice
pick, having the Kevlar layer on the outside might not make much
difference. In any event, having it on the outside is better than
nothing.

Fresh Breezes- Doug King

------


Actually I was just pondering this as there are frequent stories about
the various partially submerged objects such as shipping containers
sinking boats. Since I am getting closer to buying a boat, I wondered if
there wasn't something that could be done to at least reasonably
increase protection from said objects. I realize you aren't going to
make it bullet proof, but any amount of improvement without too much
tradeoff in weight, etc, may be worth it. Peace of mind sort of thing.
Thanks.

Red

steel hulls? adding armor to FG hulls
 

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.