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.