Engineering work has begun on the Moonen 133 — the Dutch yard’s largest yacht to date.



Expected to be called Sofia III, the 133 will have two noteworthy differences in comparison to other superyachts of her size.



Firstly, she will have a submarine — becoming the smallest yacht to do so. The two-person sub — from U-Boat Worx — will be stowed on the swim platform and launched via hydraulics.



Secondly, Sofia III will feature five guest staterooms — four below decks and one just aft of the wheelhouse. The master suite will be in the traditional location forward on the main deck.



Other highlights include a teak-lined skylounge on the wheelhouse deck.



The all-aluminium, round-bilge displacement yacht should also top out at 14.5 knots thanks to twin Caterpillar C32s.



The owner previously owned a Moonen 84 and a Moonen 97. Like those megayachts, as well as other Moonens, Sofia III features styling by René van der Velden and interior design from Art-Line Interiors.



Expect her to debut at the Monaco Yacht Show in 2012.