Shaping Hulls

About thirty years ago a steel boat was being built, I think in Australia that was two football shaped pieces of steel fastened together along the perimeter with a charge of blasting powder between the halves. The assembly was put under water and after detonating the explosive charge the two halves were separated. One end was cut off each and replaced by a flat piece of steel to become the stern. You got two boats out of each setup. If I remember it right the shape was very nice. What ever happened to the technique? Does anyone know anything about this method of shaping hulls?

 

Hi Robert,

Yes, about 12 years ago I read an article in a magazine (cannot recall which) of a similar construction method in Australia. They actually formed the shape of the hull into the ground with concrete, lay the aluminium plate in and over shape, thrown in a couple of kilo's explosives, put the lid on, and ignite the big bang.

The hull is perfectly shaped and build in a flash. Should see the photos.

Yep, the Assies are a breed apart.

Fair Winds

Wynand

 

It didn't work well enough to be a success, but it was an ingenious idea. The problem is the chance of ending up with an expensive boat load of distorted plate if it goes wrong.

 

The boat was a sailing vessel about 30 feet long and they called it a "dynamite 30" or "gelegnite 32" or something similar. I remember they used 3M VHB tapes to stick the hull longitudinals into the hull after the explosive shaping, to avoid subsequent weld distortion. I read a test on what I assumed was a production vessel, but I have never seen one. They were made somewhere on the east coast of Australia. One of the big problems I recall with this technique is controlling the flow of metal when it gets stretched. It easy to tear great holes in the plate if there is not enough metal. The former they used was made of 20mm x 20mm square steel bar only a few mm apart and they welded the alloy plate into an approximately boat shaped box before putting it into the former, filling it with water and then adding a few sticks of gelegnite.

As Mike said, it could be an expensive learning curve.

 

This was a great method for shaping large metal components, and was used for making some of the components for the apollo lander. They had it figured out well enough.

 

You can find a chapter about explosive forming in book called Boatbuilding with Aluminium by Stephen F. Pollard.
honestly: its not so impressive, I would bet for stretch forming instead of explosives. Anyone out there having money to finance a a stretch forming press with 1.5GT facility to form a nice 45 footer in one piece? I am in.