When the boat stops and primer is flat, does it remain flat or slowly re-inflate?
If it remains flat it sounds like there is a complete blobk between the primer bulb and fuel tank. If it slowly re-inflates, there is a partial block (stating the obvious I guess).....
The fact the primer bulb goes flat would suggest hose to engine is OK and problem is after bulb (or valve on the bulb itself).
for similar issue I am having.
Fact it clogs when it's rough suggests sediment in the tank (as fuel gets picked up from bottom of tank so if there is crud at the bottom it'll get sucked into the tank outlet). Do you have an inline filter? This could also be blocked