This motor has little history online that I could find n 2017. (I am always hopefull some great archive will come online!)

The only reference to a VACA outboard motor is given below. I may have absolutely no relevance. It is an article on pre-1945 Berlin motors, inboard and outboard. (This is a Google translation with tweaks.)

Vaca Mechanical Engineering

The centrifuge manufacturer Georg Kersten converted his company in 1924 into theVaca Maschinenbau Gmb H.

The company was located in the Oberschöneweider Slabystraße.
In 1925 appeared his advertising announcements of two new products: firstly for the VACA stern motor of 3 hp power, also for Kerstens two-cylinder, ball bearings 5/6 PS built-in engine with reverse gear.

1931 it was renamed, after a company relocation to the Liebenwalderstraße (in Wedding) »Vaca engine factory E. Dietrich <<.
From 1934 this production ceased.