Looks like a very heavy object. What is the purpose of this thing?I could only find a few photo references and worked out the distance based upon a full size unit sitting on top of a 600mm paving slab!
I wonder of your design is a bit "fat" and should be longer and slimmer to give a better look? Maybe increase the length of the cones?
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I suspect that there are different sizes of Torpedo Vents, certainly the ones on the Southern Carriage have the look of being sat on by the Jolly Green Giant.