Systems and methods for optimizing driveshaft coupling of marine propulsion device

An outboard marine propulsion device for a marine vessel, comprising:

• a cowling structure;
• a first shaft operably coupled to an engine and having a first plurality of internal splines;
• a second shaft having a second plurality of internal splines, wherein the first shaft is generally parallel to the second shaft;
• and
• a coupler having a cylindrical shaft that extends from a first end coupled to the first shaft via a first plurality of external splines interdigitated with the first plurality of internal splines to a second end coupled to the second shaft via a second plurality of external splines interdigitated with the second plurality of internal splines such that torque generated by the first shaft is transmitted from the first shaft to the second shaft to propel the marine vessel and wherein the coupler is configured to isolate the second shaft from torsional vibrations of the first shaft;
• wherein the first shaft, the second shaft, and the coupler are disposed within the cowling structure;
• wherein the coupler is fabricated from at least one of titanium and a titanium alloy;
• wherein an outer diameter of the cylindrical shaft is less than a maximum diameter of the first plurality of internal splines and a maximum diameter of the second plurality of internal splines;
• and
• wherein no portion of the coupler extends radially outward of the first shaft or the second shaft such that a flow of oil from the engine past the first shaft and the second shaft is not impeded by the coupler.