On Sat, 18 Aug 2007 17:45:11 -0700, "
wrote:

As built to typical
scantlings wooden boat construction is lighter but weaker than steel
construction. In small craft the difference is very significant
because of minimum practical plate thickness.

Lots weaker. 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. Same with the canoe. No maintance
whatever for fifty years, with the aluminum boats. It is true that
welded construction does require a minimum thickness. Not so riveted,
you get to use all of the weight, instead of unnecessarily strong and
heavy steel. Aluminum is thicker than steel for equal strength, so it
is stiffer, strength to weight ratio being the same as the steel. For
equal strength wood is stiffer than metal, because it is thicker. I
much prefer metal to wood or fiberglass. Light weight, zero maintance
what more could one want? Metal is noisier. Wood is quieter, give or
take the moaning and groaning, which the engine and/or wind will drown
out. In conclusion, welded steel is not optinum for boats under about
fifty feet. Steel tends to warp from the expansion when you weld it,
so you have a minimum thickness and a minimum sized boat, assuming you
want to use the strength of the steel efficiently. At one hundred
feet, you can use 1/4 inch plate. That is much easier to weld than
sheet metal.

Casady

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