You need to be able to use the image host (imgur works, as does googlesites) and then get a URL for the uploaded image (Shipbucket does not support direct uploads at this time)
For example, Based on the image you've linked to on dA, you would do this:
[img]http://fc01.deviantart.net/fs70/i/2014/312/d/f/updated_m_v_united_states_2_superliner_concept_by_mdstras-d844qpr.png[/img]
Resulting in:
Now, this is obviously not in shipbucket scale, and I would like to know if it was done in shipbucket scale? If it was, then you need to fiddle around with the settings for people to download your work on dA so that you can get the direct link to the full size file (I'd also strongly suggest you put it on template). If not, then this thread is actually in the wrong place and should be moved to the Non-Shipbucket Drawings section of the message board.
Edit: After closer inspection, you've used Shipbucket parts, which puts you subject to the Shipbucket Fair Use Agreement, which stipulates templates and crediting rules. Also, watermarks are frowned upon.
Sincerely,
TimothyC