"Lew Hodgett" wrote in message
...

"Richard Casady" wrote:

Strong as wood, heavy as steel, about sums it up.

Steel is lighter than wood. of equal strength. Aluminum is lighter
than wood. For the same weight aluminum and steel are equally strong.

Compared to an Airex cored hull with epoxy and knitted glass skins, all of
the above are a joke.

Lew



wel my Zodiac.....

"Richard Casady" wrote:


The very best plastic may be stronger. I think if Boeing is using it
that says something.
Be interesting to see a table comparing the S/N for various materials.
I know the latest fiberglass [and other plastic] is a lot better than
it used to be.
Been my experience that the older fiberglass boats are heavier than a
comparable aluminum boat.
snip

Most existing "fiberglass" boats are polyester resin with woven roving and
mat.

Woven roving is coarse compared to knitted material and requires the mat to
retain the polyester resin.

About the best glass/resin ratio you can expect is 35%Glass/65%resin which
produces a heavy laminate.

Polyester is also more brittle than epoxy resin.

Polyester is also NOT an adhesive which is why you see holes thru the
plywood used for bulkheads with the glass going thru the hole. It provided a
mechanical means of bonding.

OTOH, epoxy is an adhesive, can take advantage of knitted glass which means
much higher glass content with less resin required.

A 50%glass/50%resin ratio is easy to obtain with hand layup techniques,
vacuum bagging can achieve even higher glass/resin ratios.

The result is a much lighter as well as stronger laminate.

Add Airex foam as a core material to the mix and it is a whole new ball
game.

You could build a dynamite hull for a 15'-20' boat using 1/2" thick Airex
foam core(6.3lbs/ft^3), and 3 layers of 17OZ double bias(+/-45degree) glass.

Translation:

3 layers of 17 Oz with a 50/50 G\R ratio= (17*3)*2=102 Oz for each laminate
skin or 204 Oz/sq yard for both skins.

The Airex: (1/2)(6.3*16*36*36)/1728 = 14.2 Oz/sq yard for 1/2" Airex.

204 + 14.2 = 216 Oz/Sq Yard = 216/9 = 24.0 Oz/Sq Ft = 1.5 Lbs/Sq ft.

Pick a metal, you will need at least 1/4" plate to provide equalivant
strength which means a lot more weight.

BTW, add a layer of 17OZ glass, say 6"-8" wide along the keelson for a wear
strip, and you are good to go.

The only problem with epoxy is that it has no UV resistance so a coat of
paint is required.

Lew

On Aug 18, 5:44 pm, (Richard Casady)
wrote:
....
As I said, steel has a better strength to weight ratio
than wood If you build similar boats, of equal strength, wood will be
heavier not lighter. My experience with 16 foot boats is that wood is
a lot heavier than riveted aluminum. ...

Volumes have been written on matteral's properties. It isn't a simple
subject and I am not a master of it. The properties of complex
structures in a complex environment are very, very difficult to grasp
from first principles. The strength of a structure is only loosely
connected to the strength of it's materials. Thus, comparing a single
property of steel and wood isn't a great guide to that property in a
complete boat.

Cruising boats aren't 16 foot tinnies. Also, you are comparing a
lightly built tin boat with a heavy wood one. Right up until the 70's
racing dingies, rowing shells, unlimited hydroplanes &c. built of wood
were lighter, stiffer and faster than glass, aluminum was not
competitive and steel was never considered. In practice, boats built
as lightly as permissible to any of the classification societies rules
to a given service will be heaviest in steel and then aluminum and
then solid fiberglass and then wood and lightest in cored glass or
exotic fiber. So, while I will not argue that a steel boat couldn't
be made as lightly as a wooden boat for a given service, such a craft
would be revolutionary. In practice, steel boats are heavy but very
durable and wood ones are light and less durable and in that context
Roger's statement seems very reasonable to me.

I don't mean to dis metal boats, many of them are great. I've got an
aluminum RIB that I'm very fond of. Riveted aluminum can be very
light and I know a guy who built a catamaran of cor-ten steel with an
ingenious space frame system that was reasonably light. On the other
hand, I remember a lovely evening in Apia Samoa when I shared dinner
and a couple of jugs of wine with three world cruisers who had voyaged
there on their steel boats. We got to talking horror stories and they
each had one to tell about putting a finger or dropping a hammer
through a bit of the hull or deck on their own boats. Localized
corrosion can be a real problem for steel boats and thin plates will
make it worse. Steel boats are always rusting and thick ones last
longer too. A riveted thin skinned aluminum boat with an electrical
system that was in the water full time is almost certain to have major
electrolysis problems. So, I'd advise caution when you attempt to
make a steel boat as light as a wooden one. Scantlings take into
account mistakes other folks have made for you...

-- Tom.

On Sun, 19 Aug 2007 14:03:55 -0700, "
wrote:

Cruising boats aren't 16 foot tinnies. Also, you are comparing a
lightly built tin boat with a heavy wood one.
Why do you say that. I have seen boats of all kinds that have hit
something, like rocks. The metal ones hold up better than wood.
All the boats I have encountered, in fifty years at the same lake
were strong enough. I don't remember with trouble with strength with
any of them. None of the metal boats needed it, but you can drill out
rivets to make repairs, and put in exact replacements for damaged
parts, and have it end up exactly as it was. Exactly.
Right up until the 70's
racing dingies, rowing shells, unlimited hydroplanes &c. built of wood
were lighter, stiffer and faster than glass, aluminum was not
competitive

Why then did they use aluminum to build all those airplanes?
The brits built some wood bombers during WWII but none survive.
They certainly were no better than metal. They got around an aluminum
shortage caused by U-Boats. All of them rotted away over the years.
They use aluminum for the floats on float planes, they are neither
heavy or weak. And as for wood, the examples you pick are scarce,
limited edition specialty boats. There are probably more than 100
metal boats for every one of the types you mention. How about a
realistic comparison. There is a guy who who makes sports fishing
boats. He molds the hull in plywood [more or less] and it is
significantly stronger and lighter than something made from 4x8
sheets: they cost a lot. Wood is no better but it always seems to
cost more.I read the writeups on the go fast boats, in Boating. The
ones made from the very best plastic. Kevlar, stuff like that. You can
get a go fast cruising boat that will cruise at 60MPH, with diesel
engines and drink a reasonable ammount. Some of those boats are about
as high tech as it gets.

As for the ordinary wood boats, the ones I have seen in the real world
are heavy. Lightweight construction may exist, but I have seen very
little of it in the real world I do my boating in Iowa, and wood
boats are very rare these days. My father's wood boat is in a museum.
I would like some of that miracle wood. You know the stuff. 3/8
planking that is as strong as 1/8 inch aluminum. Wood was not only all
there was not so long ago, it was actually affordable. Those who like
wood can still get it, but it is far from cheap, unfortunately. The
best plastic is much more expensive than metal. Where I come from
nobody will do the maintainance that wood requires. The very best and
most expensive aircraft grade sitka spruce is just about as strong as
the very weakest aluminum available: pure aluminum, with no copper or
magnesium to harden it. The stuff used for outboard engines for the
corrosion resistance in salt water. And for beer cans. The cans are
..006 inch thick. You can't do that with fiberglass.
Casady

On Fri, 17 Aug 2007 19:27:28 +0700, wrote:

The reason that ferocement boats have a bad reputation is because
people used to b build them in their back wards and when it came time
to plaster them would get a bunch of beer and all their mates in. some
of these were pretty horrible. Other people were smart enough to have
a professional plasterer do the job and never have a problem.

I think they are far too much work for what you get. Steel is a good
material for a homemade fifty footer.

They are heavy for their length though and you'll probably find that
you can carry a lot more sail then the fiberglass boats.

Put enough ballast in the glass boat to bring it up to the weight of
the cement boat, and _it_ will carry more sail. Ferro is just plain
inefficient. It can be fairly cheap if your own time is low priced,
but the hull is usually a small part of total cost. Someone once said
it had all the charm of steel and the strength of wood. That, of
course, is unfair to both steel and wood. Steel can be beautiful, but
only if the plates are thick enough to weld properly. Fifty feet is
minimal, seventy five or so is good. Wood can be strong, but it does
cost too much. Cutty Sark is wood and they had a fire. I think the
iron frames are OK.

Casady

Casady

On Fri, 17 Aug 2007 08:52:17 -0400, "Roger Long"
wrote:

Strong as wood, heavy as steel, about sums it up.

My inland lake fishing boat is 22 feet of riveted aluminum. It has a
bow locker with two tiny bunks. Too thin to weld. It is both strong
and light and I love it. It cost two grand, and if the available steal
had been glass, I would have that. Steel is either too thin for good
welding, or too heavy, in anything smaller than maybe seventy five
feet. You can perhaps rivet that stuff too. Aluminum killed the wood
boats before there even was glass. Where I do my boating there are a
bunch of aluminum boats mostly fifty years old, no maintainence ever,
and lighter than the wood they replaced. Aluminum is good, but it is a
bit noisy in the sheet metal type thicknesses. Of course, destroyer
hulls were famous for noisy oil canning. Why they called them tin
cans. Quarter inch plates.

"Richard Casady" wrote in message
...
On Fri, 17 Aug 2007 08:52:17 -0400, "Roger Long"
wrote:

Strong as wood, heavy as steel, about sums it up.

My inland lake fishing boat is 22 feet of riveted aluminum. It has a
bow locker with two tiny bunks. Too thin to weld. It is both strong
and light and I love it. It cost two grand, and if the available steal
had been glass, I would have that. Steel is either too thin for good
welding, or too heavy, in anything smaller than maybe seventy five
feet. You can perhaps rivet that stuff too. Aluminum killed the wood
boats before there even was glass. Where I do my boating there are a
bunch of aluminum boats mostly fifty years old, no maintainence ever,
and lighter than the wood they replaced. Aluminum is good, but it is a
bit noisy in the sheet metal type thicknesses. Of course, destroyer
hulls were famous for noisy oil canning. Why they called them tin
cans. Quarter inch plates.

What is this repeated comment about "steel...too thin for good welding"?
Unless we're talking about foil, thinner guage steel (16 or even 18 ga) is
entirely weldable. I should think 1/4" steel would be excellent for
below-the-waterline on a 35 footer, perhaps going to 1/8th or 3/16ths above
the waterline and for decks. Frames could be trussed to achieve strength
without excessive weight. I believe that the biggest reason for having
extreme thickness in steel hulls is to provide more material that can be
lost to corrosion before compromising the hull. But with modern epoxy
coatings, perhaps overlaid with glass or some other material for abrasion
protection (to protect the epoxy barrier), this could be made unnecessary.

Just thinking aloud.

On Fri, 17 Aug 2007 08:52:17 -0400, "Roger Long"
wrote:

Does that sound like a way to build a boat? Worse the steel, which
should be the tensile material on a thin shell, was on the inside and the
concrete, a material most effective in compression, was on the outside.

That is why they invented prestressed concrete. Tension on the steel
keeps the concrete in compression. The design allowance for tensile
strength of concrete is zero. Opposite of chain, which has no
compressive strength. Materials science is a facinating field of
study. They generally cover steel building framing with concrete, but
it is just fireproofing for the metal. On the other hand, they do use
actual reenforced concrete for similar structures, and they can look
similar on the outside.reenforced concrete that looks about like the
covered steel.

For something more efficient consider the submarine, with two
concentric shells and all the frames between. Those things were strong
enough to handle any wave imaginable. Big waves just cover them and
then move on.They don't flood when they get swept, after all. Then
there is the other sub. the fabric one. Gunny sack, cat, and brick.
Just kidding, we love our four cats. We got them from a shelter that
doesn't kill animals, they will keep them forever.

Casady

"Richard Casady" wrote:

Steel is a good
material for a homemade fifty footer.

Steel is a bloody joke.

My epoxy/knitted glass/Airex cored hull has stopped a copper jacketed
..357 mag dead, and it doesn't rust.

How much steel is required to stop that .357?

Lew

On Tue, 21 Aug 2007 22:27:43 GMT, (Richard
Casady) wrote:

On Fri, 17 Aug 2007 19:27:28 +0700, wrote:

The reason that ferocement boats have a bad reputation is because
people used to b build them in their back wards and when it came time
to plaster them would get a bunch of beer and all their mates in. some
of these were pretty horrible. Other people were smart enough to have
a professional plasterer do the job and never have a problem.

I think they are far too much work for what you get. Steel is a good
material for a homemade fifty footer.

The thing that made fero boats popular was that they were cheap to
build. The armature is mainly cheap re-bar and chicken wire, a few
bags of sand and cement, case of beer for your mates, and you got a
hull.

They are heavy for their length though and you'll probably find that
you can carry a lot more sail then the fiberglass boats.

Put enough ballast in the glass boat to bring it up to the weight of
the cement boat, and _it_ will carry more sail. Ferro is just plain
inefficient. It can be fairly cheap if your own time is low priced,
but the hull is usually a small part of total cost. Someone once said
it had all the charm of steel and the strength of wood. That, of
course, is unfair to both steel and wood. Steel can be beautiful, but
only if the plates are thick enough to weld properly. Fifty feet is
minimal, seventy five or so is good. Wood can be strong, but it does
cost too much. Cutty Sark is wood and they had a fire. I think the
iron frames are OK.

I've never argued that they were efficient or anything else except
cheap to build.

It isn't as strong as steel, for sure, and (to my mind) have very
little charm

I've seen 35 foot steel boats built in Holland that were as fair as
any boat you care to look at. Of course they were built at
professional yards that do nothing but steel boats and their cost
quite a lot more then you would expect.



Bruce in Bangkok
(brucepaigeATgmailDOTcom)