"Fully Forged Rotating Assemblies", it sure sounds impressive, but what does it really mean for the person who just want s a boat that runs reliably and knows nothing about engines? Before we explain, know that this is one of the most important factors in the performance AND long life of any engine. Which is why it is a standard feature on Medusa and something most other manufacturers cannot claim.
The rotating assembly is the group of components in the engine that move, or rotate, during engine operation. The parts that bear the brunt so to speak, with names like crankshaft, connecting rods, pistons, camshaft. So, the stronger the material these parts are made of, the easier longer they can do it without suffering any stress or weakening. And in metallurgy, we have two choices to make these parts, casting or forging.
Casting is the process where metals are molten and then poured into a mold to create the part. Thousands of parts can be made this way very quickly. Casting also makes it easy to use alloys, since different metals can be added during the molten phase, and they tend to be lighter, all of which are positives. On the negative side, cast parts are weaker since they develop porosities and cracks during the process, sometimes even voids, all of which may lead to catastrophic failure when exposed to high workloads.
Forging is a much more difficult, time consuming and costly process, which involves heating and bending the pure metal while still keeping it in solid state until the part is formed. It is more of a "hand crafted" process, which not only allows better quality control over parts but yields metals with refined grain and recrystallized structure, which results in superior strength against deformation and shear impact.
It makes sense therefore to use rotating assemblies that are forged instead of cast, even if modern castings may be more than adequate for automotive use. But once again, marine requirements are far higher, and it only makes sense to use the strongest available components when designing an engine which we hope will last for decades without need for repairs. But let's not forget that cast is much cheaper than forged, and the lengths to which manufacturers will go in their obsessive quest to save a couple hundred dollars on an engine that retails for $20,000 (theirs, not ours). So when reading engine specs, don't be confused by terms like powder metal, hypereutectic, brushed or polished. If it doesn't say "Forged" it is not up the highest standard, and therefore, it is not a Medusa.