Extreme Lightweight Aluminum Construction

In the case of, for example, an open skiff, lightweight methods such as swaged panels are well established, flat plating dooms the boat to be much heavier to limit dishing. But in such a boat, the shell is a big proportion of total weight.

 

In addition, the puncture resistance of thin plate, no matter the ring frame spacing, is seriously compromised.

For inshore, closed course racing, this might be an option. For any serious cruising................Bleh!

 

We found that "method" - closely-spaced internal structure and thin skin - to be the better option for hydrofoil-assisted catamaran and trimaran hulls from a structural design standpoint. But for a given volume/displacement, the hulls were not necessarily lighter than those with more traditional frame and longitudinal spacing..they were simply better suited to being dynamically supported at specific loading points.

 

Derecktor specialized in aluminum sailboats including several 12 meters for America's Cup competition and high-end motor yachts. Cost is not a major consideration for some of those boats. Also, the panel stiffness, etc requirements, especially for racing sailboats, may be considerably different than the requirements for commercial and military vessels.

 

How common are point impacts that penetrate hulls ? The majority of failures are splits and cracks from wave impacts, and I am not sure thinner material is necessarily more susceptible.

 

I appreciate your input Ad Hoc; thanks.

 

I appreciate your input PAR; thanks.

 

I appreciate your input Mr Efficiency; thanks.

 

I appreciate your input messabout; thanks.

 

I appreciate your input BMcF; thanks.

 

I appreciate your input DCockey; thanks.

 

Mr E. I concur that point impacts are not a frequent occurrence, maybe never with a little bit of luck. On the other hand it only takes one such incident to spoil a perfectly good day.

Did you ever see the movie with Robert Redford; All Is Lost ? He was sailing solo, somewhere north of Oz, and ran into a wayward floating container.

A thin skin will pant more than a thicker one, more or less in proportion to the third power of thickness. Increased flexure will eventually cause the aluminum to work harden, becoming somewhat brittle. It can eventually crack from the wave action that you have mentioned.

Even the slightest rippling in the forward sections of the boat will be counter productive as Marchaj and others have shown. A thin skinned boat might do better with a whole gaggle of longitudinal stringers as opposed to ring frames. Only a few frames would be needed and none of them would touch the skin. A less labor intensive build too.

 

Sorry that's incorrect.

Aluminium is a ductile material and fails 99.9% of the time through ductile fracture. (There are rare conditions that can exist when brittle fracture may occur).

Work hardening simply reduces its ductility, that's all.

 

I'm not familiar with the particulars of the thread subject method, but thought it might be interesting to mention two techniques (that are not new by any means) which help in reducing labor and wieght in aluminium construction.
1. One of the other engineers here will know the name of this because I don't recall what it is, but there is a module for AutoShip that preditcs how sheet metal will bend. This allows for plasma cutting large panels for the hull in pattern that will lay on the frame, bend into position and butt tightly. On smaller craft each side of the hull can be made from one sheet of aluminium resulting in only one weld up the keel. Less welding = less heat distortion = less fairing compound = less labor.

2. I'm not certain this method regularly applied in Marine Construction but I think I can logically assume it certainly has; When Lotus builds their very light and very rigid sports car frames they use aluminum extrusions that epoxied together rather than welded with a few rivits in key areas, but the rivits are mostly for alignment and clamping pressure. This is such a brilliant technique, I am huge fan of the Lotus Elise & Exige sports cars. It saves labor and QA time by eliminating welding (plus the cost and maintenance of the welding equipment) and there is actually a small weight savings with epoxy vs weld beads.

 

Your description sounds like "unrolling" a developable surface. Not all hull surfaces are developable. For example the boat shown under construction in post #3 will not have a developable surface.