Using the sprint key for the boat stays when exiting and you keep the boost forever until you press the sprint key again while on foot.
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Sprint is set on hold. Leaves no particles behind when I am sprinting on the ground, FOV and speed stay the same. No loss of hunger happens like it normally would when sprinting for long periods of time.

Essentially how I did it was: Get in boat, press left control to go fast in the boat, drive boat towards shore and exit boat while holding the W/forward key. Normally when you exit the boat with sprint toggled on hold, it will turn off sprint and you will walk normal upon exiting the boat. In my case, it did not toggle off and I retained the speed. It showed no particles and no increase in hunger depletion as if I was speed-walking at sprint speed rather than actually sprinting. Only ways to stop the effect were to sprint again, either on land or in the boat.

Affects for 1.16 Pre-release 5
Can confirm in 20w51a.
This ticket is actually a duplicate of MC-30403.
Do you have sprint set to toggle or hold?