Simple idea, kinda.

I don't understand how you are going to add a top to a 12" half cylinder and make a cabin out of it.

 

Yes indeed, please post pictures and maybe have someone video the cutting part, from a distance.

All the best!

Great project.

 

Not sure about that...
I was watching a fitter cut the top off an empty 44 gallon drum of motor oil with an oxy torch.
Just as he was finishing the cut it went bang! It must have gone 200 feet in the air, missed his head by 1 inch.
He had a black face, no eyebrows, and all his hair was sindged. The startled expression was priceless.
Cracked me up for weeks.

You might want to have a quick look here.....
http://www.osha.gov/pls/imis/AccidentSearch.search?acc_keyword="Diesel Fuel Tank"&keyword_list=on

 

I've just realized, OP stated 12 - 14 FEET by 60 FEET!

LMAO!

 

Diesel will explode if hot enough (at flash point) and the fuel/air mix is right--- sometimes more impressive than gasoline.
Who wants to be a "Half Tanked" boat builder!

 

You could cut it with water under pressure. Or flood it with CO2, then use a torch. All our carriers can do that to the whole flight hanger and ammo storage areas and that saved the Lady Lex at Midway-one of the first to be able to do that. Lots of topside fires--none below. The Japanese did not know about this and 4 of theirs were sunk.

 

Doesn't using a car exhaust to purge the tank also work ?

 

Don't use a torch on a diesel tank. The heat gasifies the residue. Fill it with water, cut it with a worm drive circular saw (with a GFI).

 

The OP seems long gone here folks...

I wonder where he/she could have gotten too...?

 

Exactly. Fuel ships use there exhaust to fill the air spaces in tanks with carbon monoxide. I have repaired truck fuel tanks with this method. I suspect sub t does not have welding experience.

 

Can you say, "Ka-Boom!"

 

When I was a teenybopper I worked in a car wrecking yard and we used the same method (car exhaust into the tank to de-petrol fume it) before brazing up any rust holes and painting.