Thanks, Manfred, I agree. One prop - and a big meaty nozzle. But my notes - and the Varenderfgoed page - have "2 x C2cyl", which normally means two separate 2cyl compound engines. But the tug's own website makes it clear that there is only one engine (dubbel compound Lentz kleppenmachine), but with two high and two low-pressure cylinders - which should be written as 1 x C4cyl.
http://www.dockyard9.nl/het-schip/
Thanks for pointing that out.

Many thanks Manfred and davidships for the information. I have made the necessary changes.

@davidships: In your provided details it says 2-screw. I think the two 2cyl are in-line working on one propeller as seen in my link in drydock:
https://www.varenderfgoed.nl/galerij/dockyardIX.html

Nice video btw!

Yes, DOCKYARD IX was "9768 B Rott 1956" - ENI 02309768
Sisters
DOCKYARD III (9761 B Rott 1956)
DOCKYARD V (9762 B Rott 1956)
DOCKYARD VIII (9764 B Rott 1956)

92grt, 25.06 x 6.31 x 2.9 (dr 2.3)m
2 x compound C2cyl 500ihp 2-screw
built 1940 Rotterdamse Droogdok Mij NV, Rotterdam (Yd 226)

1942-1978 Rotterdamse Droogdok Mij NV, Rotterdam
1978 sold for 1 guilder to City of Rotterdam for preservation at Maritiem Museum Prins Hendrik, Leuvehaven (mng Stichting Dockyard IX)
1994 Stichting Buiten Museum

Here's the important part:
https://www.youtube.com/watch?v=QSiehhTeeMM

Might be DOCKYARD IX which contains the number 768:
https://www.varenderfgoed.nl/galerij/dockyardIX.html