It depends on whether it's a wood planked boat hull or a plywood hull.

Applying an epoxy barrier coat primer isn't needed on wood planked boat hulls because water will swell the planks, preventing water intrusion. A barrier coat is also not recommended in this case because if the boat dries out, there'll be gaps between the planks that the barrier coat can't fill, and the barrier coat will retain moisture, which promotes rot.

You can apply a barrier coat primer to a plywood boat hull and to wooden boat parts that don't rely on the wood to expand to keep the water out, but you have to completely encapsulate both sides of the plywood in barrier coat in order to prevent rot.