Conversion question for the group Alu-Steel

Get a copy of Dave Gerr's The Elements of Boat Strength, International
Marine, 2000.

It's not a great read, but it is a clear, easy to use reference for
figuring out scantlings in any boat between 10 and 120 feet.

Having given you a reference that might let you think you could do it
yourself, let me point out that this is a complex subject,
particularly in a boat big enough to use 3/8" steel hull plate. The
aluminum boat will be much lighter, so you will have to add weight to
bring her down to her lines. In a powerboat this has to be done very
carefully, as it would be easy to make her too stiff -- boats that are
too stiff have a sharp, stomach-wrenching roll, but not stiff enough
and they capsize....

In a sailboat, the knee jerk reaction is to simply add weight to the
keel, which is good for sail-carrying ability, but means that you will
have to make the rigging stronger.

In short, you can't change just one thing. It might be a good time to
consult a naval architect. Gerr is very accessible and willing to
think outside of the box....

Jim Woodward
<a style='text-decoration: underline;' href="http://www.mvfintry.com" target="_blank">www.mvfintry.com</a>


Techie <nomail.RemoveThis@here.net> wrote in message news:<Xns93DFCEE0ED097nomailherenet.RemoveThis@140.99.99.130>...
 > If a plan for a ship calls for 3/8" thickness in steel hull, what would
 > that be app. in Aluminium instead?<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Conversion question for the group Alu-Steel 

With the emphasis on "approximately", aluminum has 60% of the strength
of steel. Algebra: 0.60 / 1.0 = 0.375 / x and x = 0.625 or 5/8"
Good luck,
Boatdreams

Techie wrote:

 > If a plan for a ship calls for 3/8" thickness in steel hull, what would
 > that be app. in Aluminium instead?
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Conversion question for the group Alu-Steel 

This is precisely why you should hire an engineer. If you only
look at strength, then your boat may fail. Stiffness is
often the governing criteria, and the spacing of frames,
bulkheads, stringers will have as much of an effect as
the thickness of the plating. Also the size of channel,
angle iron, etc will be different between aluminum and steel,
resulting in a whole new set of calculations. All these
dimensions are interelated, and making sure that things fail
in the right order is part of a good engineering analysis as well.

"boatdreams" <sclaass.TakeThisOut@softcom.net> wrote in message
news:3F4D98C0.4000200@softcom.net...
 > With the emphasis on "approximately", aluminum has 60% of the strength
 > of steel. Algebra: 0.60 / 1.0 = 0.375 / x and x = 0.625 or 5/8"
 > Good luck,
 > Boatdreams
 >
 > Techie wrote:
 >
  > > If a plan for a ship calls for 3/8" thickness in steel hull, what would
  > > that be app. in Aluminium instead?
  > >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Conversion question for the group Alu-Steel 

Have mercy. The guy just wants a rough approximation to play around
with. His architect may find that 1/2" or even 3/8" alloy meets his
needs. Lacking particulars, the 60% rule is a starting place. By the
way, does anyone know the current price difference between 3/8"
(5.4#/sqft) and 5/8" (9#/sqft)5086 aluminum alloy plate? I think
3.6#/sqft savings in the hull alone would be a good incentive to hire a
professional. Regards,
Boatdreams
-------------
Matt/Meribeth Pedersen wrote:

 > This is precisely why you should hire an engineer. If you only
 > look at strength, then your boat may fail. Stiffness is
 > often the governing criteria, and the spacing of frames,
 > bulkheads, stringers will have as much of an effect as
 > the thickness of the plating. Also the size of channel,
 > angle iron, etc will be different between aluminum and steel,
 > resulting in a whole new set of calculations. All these
 > dimensions are interelated, and making sure that things fail
 > in the right order is part of a good engineering analysis as well.
 >
 > "boatdreams" <sclaass DeleteThis @softcom.net> wrote in message
 > news:3F4D98C0.4000200@softcom.net...
 >
  >>With the emphasis on "approximately", aluminum has 60% of the strength
  >>of steel. Algebra: 0.60 / 1.0 = 0.375 / x and x = 0.625 or 5/8"
  >>Good luck,
  >>Boatdreams
  >>
  >>Techie wrote:
  >>
  >>
   >>>If a plan for a ship calls for 3/8" thickness in steel hull, what would
   >>>that be app. in Aluminium instead?
   >>>
   >>>
 >
 ><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Conversion question for the group Alu-Steel 

Matt/Meribeth said:

 >All these
 >dimensions are interelated, and making sure that things fail
 >in the right order is part of a good engineering analysis as well.

Ahem!!
A perfectly engineered structure shoul fail all at the same time - totally
disintegrating to molecular levels. At least, that's how Herreshoff saw it.



Steve
Stephen C. Baker - Yacht Designer
<a style='text-decoration: underline;' href="http://members.aol.com/SailDesign/private/scbweb/home.htm" target="_blank">http://members.aol.com/SailDesign/private/scbweb/home.htm</a><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Conversion question for the group Alu-Steel