To check this I avoided taking 'tons' literally because it should be 1 ton equals 100 cu ft. This gives a total of 1,500 cu ft and as the side elevation of the tanks is 108 sq ft, the width (which cannot be seen on the blueprints) must be just under 14 ft, i.e. 7 ft per tank, which makes sense given the width of the ship at this point being about 16 ft.
While I am at it, I can report that the rusty, truncated ventilation funnels are now restored and looking very smart (if I say so myself!). (Photos)
Painting inside these funnels was rather tricky and my hair, which has been silver for a few years, now has small patches of grey, biscuit and red. My wife refuses to cut these out, so I have to wear a cap in public – which I should have worn while painting! (No photo)