Can a Magnetohydrodynamic Drive Work Without a Tube?

[Godspanther]

Now the designs I've seen involve water flowing through a tube but is a tube really necessary? Can the design simply be turned inside out so that rather than pushing water through a tube a regular ships hull could just pull the vessel through the water?

 

[Baluncore]

The problem is making a strong magnetic field. The tube passes through the poles of a magnet with an enclosed short magnetic path.
An external magnetic field would upset the compass and radiate energy. It would also require electrodes on the outside of the vessel hull.

 

[Godspanther]

Mmm.. I see. What if the hull is ridged like a piece of corrugated metal? The magnets could be placed in the ridges. Then instead of passing thru one magnet between the poles it could pass between the opposing poles of two different magnets. Of course in total the hull would have many such opposing magnets.

 

[Baluncore]

What if the hull is ridged like a piece of corrugated metal? The magnets could be placed in the ridges.

Which would require an electrode outside the hull, making the corrugation a tube.

If the hull was magnetic material like iron, the magnetic field would follow the hull surface, not pass through the water. A conductive metal hull like aluminium would short circuit the electrodes and corrode.

See here for internal or external flow.
https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive#Typology