Keeping Belgium as dutch territory requires a point of divergence prior to 1900 though. Boosting dutch naval power to the heights proposed remains a significant challenge simply because of the costs involved and the recession during the 1920-1930.
The most plausible point of divergence seems 1918 following the end of the first world war. OTL there was bad blood between the Netherlands and Belgium because the latter accused the Netherlands of not being neutral due to the Netherlands allowing German forces to withdraw across dutch soil.
OTL Belgium demanded pieces of Dutch territory to be turned over, but the population of said territory pledged loyalty to the dutch monarchy. In the end the Netherlands would provide the funds for a canal between Antwerp and the sea.
WI the situation turns out different. The Netherlands does not allow German forces to cross dutch soil, Belgium refugees bring back stories about dutch hospitality AND the class system within the Belgium military (French speaking officers from Walloon commanding dutch speaking soldiers) drives Flanders into separation from Walloon.
Flanders joins the Netherlands and Walloon joins France. After negotiations the Netherlands take custody of Belgium Congo and its resources.
With a larger coastline and more territory to control the Rpyal dutch Navy may invest in several battle cruisers earlier, possibly this design:
https://en.wikipedia.org/wiki/Design_1047_battlecruiser
Keep in mind that this is merely a brain fart, since ww1 and the interbellum is not my area of expertise i cannot say with a degree of certainty how plausible this scenario is.