There was no electricity therefore no refrigeration and the only fuel source to provide hot food were wood burning stoves.
Meat and fish was dried and salted to be stored in barrels. There would have been few vegetables once the ship had been at sea for any length of time. Fruits were unheard of except perhaps apples stored in barrels. Hence the expression "one bad apple" would contaminate all within the barrel. It must have been soul destroying to open up a fresh barrel of apples only to find that they were all bad and had to be thrown over the side.
With no fresh vegetables and little fruit, the sailors diet was seriously deficient in vitamin C. The result was a common disease known as scurvy. To overcome this Royal Naval ships crews were given a daily ration of Lime juice and even in my days in the Navy this ration is still made available when certain arduous conditions prevailed. This was noticed by the American before the war of independence and hence the English are still referred to as "Limeys" to this day.
Larger ships would take to sea with live animals to be butchered and eaten at a later date and as the journey length was dependant on the wind and weather, it would have been extremely difficult to plan domestic arrangements with any certainty.
In bad weather with the ship being tossed like a cork on the waves, the wood burning stove was a dangerous device which if it got out of hand would consume the wooden ship. In extreme conditions hot food was difficult to provide and yet most foods would require cooking to kill the bacteria and make them edible.
The ships carpenter would make plates for the crew and the easiest way to make a plate was to cut a square section piece of wood. Square shaped plates could be stowed away easily and wooden ones would not break irrespective of how violent the ships movement might become. There was no sort of turning machine to make round plates and that would have been seen as an unnecessary expense.
So when the sea state allowed and there was sufficient food available, every effort would have been made to provide the crew with a hot edible meal. This would have been collected from the galley and eaten with relish on the mess deck table utilising the square section plate.
Therefore if you achieved "Three Square meals a day" you were doing very well. An expression still used today in everyday English.
--Wizard's note: Before you write me - I realize that the ship pictured is one of Chris Columbus' from Spain...