Setting up a health system.

[Windspar]

BoatSprite class add health variable.

self.health = 3

For your groups you can have on for boat enemies.

        self.bullet_group = pygame.sprite.Group()
        self.pirate_group = pygame.sprite.Group()
        self.croc_group = pygame.sprite.Group()

Can be replace by.

self.boat_enemies_group = pygame.sprite.Group()

Then boat losing a life. Check all objects in the list. Returns all objects that boat collided with.

# Colliding
        hit = pygame.sprite.spritecollide(self.boat, self.boat_enemies_group, False)
        if len(hit) > 0:
            self.boat.health -= 1
            if self.boat.health == 0:
                # boat dies

All your draw code for the scene should be under draw method.

    self.surface.blit(self.heart, (600, 20))
    self.surface.blit(self.heart, (600, 50))
    self.surface.blit(self.heart, (600, 80))