Depending on how you define "going straight" on a sphere, it may not be the same as going at constant heading.
VR is unclear on this topic, but as far as I know
- When using a fixed heading (no TWA, no waypoints), the boat moves on the loxodromic (rhumb line), that is, it keeps its course angle.
- When using waypoints, the boat moves on the geodesic (great circle) instead, thereby slowly changing course angle. After passing the last waypoint, it keeps whatever course angle it has at that point.