The 50 hp rating for the engine was very optimistic, as no one in their right mind would run it at that high a rpm
That is like a car rated at 200 HP, but only idiots would run at full throttle and harvest the 200 hp continuously.
I have used all 51 HP of the Perkins
a few times for emergencies only and it sure works, plenty of power available if you have the right size prop.
Some guys over-prop their boats so bad the full HP can not be obtained, or the 4-108 is installed in boats too big for the engine.
I ran a Jouet 42 with a 4-108, seemed a good combo and so was my CSY 33
44s came with the 4-154 rated at 62 HP, perhaps a bit on the light side)
The highest time 4-108 I heard about was 15,000 hrs on a CSY 37
in St. Croix, even at those hrs the engine was still running fine.