Hi there! HP of the ship is maximum hp you can advance to, so when you leveling up, you spend points on hp, having better ship lets you buy more hp. Same with cannons, you need to spend points on cannons when advancing a level to be able to equip more cannons. So buying better ship doesn't grant you max hp, and max cannons, you need to equip your ship with them, then you can upgrade cannons in cannon shop.