Ship's biscuits would have been a major component, and there were substantial manufactories for these products in all the British (and probably American) port cities. Machine-made by the 1850s and 1860s, they were from cheap flour, made in shapes but cut so that they could be easily broken apart into regular pieces, and baked so that they were as dry as a bone. They could last for decades if they stayed dry, and I've seen accounts of people in the early twentieth century getting a biscuit while on a tour of a ship (like on a holiday), and then tasting the biscuit literally decades later (that was somewhere in the Huntley and Palmers Archive at the Museum of English Rural Life in Reading, England).

As for just how much they would take, I don't know. The only thing I've encountered that's close to what you're asking about is William Henry Dana's Three Two Years Before the Mast, an account of a trading expedition from Boston to California in the 1840s. Not a whaling trip, to be sure, but they followed the same route from the North Atlantic to the Pacific, and they certainly encountered whaling ships along the way. A few things stand out. One is that they took on provisions wherever they got a chance, water in particular but meat, fruits, and vegetables as well. Dana describes getting beef at some of their stops in California; he says that the port closest to Los Angeles (presumably today's San Pedro) was three Englishmen living in a tiny house on top of a bluff, surviving on beef and beans while they helped unload ships and transport goods to the then-tiny city of Los Angeles, thirty miles away. Another point that stands out is on their return journey, around Cape Horn, they were fairly low on provisions as they sailed past Brazil. They met another ship, and purchased bags of potatoes and onions from them. So desperate were they for fresh foods that the men ate the onions raw, as you'd eat an apple. The smell of men who'd been at sea for months, eating straight onions... wow.

Ok, since I seem to have put my foot in my mouth I am going to draw from an old project cataloging worklore in The Making of a Sailor or Sea Life aboard a Yankee Square-Rigger by Frederick Pease Harlow to see if I can't give you some more specific information about shipboard food in the late 19th century. Harlow sailed from Boston to Melbourne and back aboard the Clipper Akbar in 1876.

93 Passing the hell ship *Lizzie J. Bigelow *

The vessel was reputed to be a “hell ship” when it was whaler. The food was poor and the men were not paid. Thus, they were unable to even purchase fruit so scurvy ran rampant onboard. When the vessel replenished her water she only stopped at uninhabited islands where the men could not run away. Deserters were caught and brought back. Alonzo’s brother deserted several times and only escaped when he had to be left behind in a hospital.

99 Warm Food and Utensils.

“The night was cold with a regular northeast snowstorm setting in. We had no stove, either in the forecastle or our room, and the only warmth we got was from a kerosene lamp that we burned without a chimney. Turning up the wick for light as well as heat, our room was soon filled with small particles of soot emitted from the wick and we were forced to open the door in order to breathe. Our room being in the after part of the forward house, the snow didn't bother us much but we were obliged to "turn in" in order to keep warm using all the coats we possessed thrown over our blankets. Ships in those days didn't furnish blankets to the crew and very few sailing vessels equipped the forecastle with a stove or dishes for the men to eat from. Each sailor provided for himself a tin pan for a plate, a tin dish for a soup-plate and a quart pot for his tea or coffee, which was made by the cook in the galley, in a ten-quart pot, sweetened with molasses which was allowed to boil in the pot while the coffee was being made. If poor Jack was rich enough he bought himself a knife and fork and tablespoon. If not, he used his sheath-knife and drank his soup from his tin dish or coffee pot. There was no table in the forecastle from which to eat, but there were always two benches for the men to sit on. The food was brought from the galley and placed in the middle of the floor, in large dish-pans, where the sailors helped themselves, filling their tin pans and holding them between their knees. If the ship was in a heavy sea, sometimes Jack would spend the greater part of his dinner-hour, balancing his coffee in one hand and holding his plate in the other, before he could get a chance to feed himself and many a time the situation would become so ridiculous that no one could eat from laughter and with each roll some old salt would say, "Who wouldn't sell a farm and go to sea!" bringing forth another round of laughter.”

124 Harlow records dinner that night. This list of food was generally consistent throughout his voyage except when the cook was lazy or the ship was out of molasses. White bread was dubbed soft-tack.

“Our dinner consisted of mutton stew, potatoes, boiled salt pork, soft-tack (white bread), ginger bread and coffee sweetened with molasses.”

146 Harlow observed his first school of flying fish. He then explains the usually system of rationing aboard ship including the “Old Horse.”

Harlow watched the flying fish. If they accidentally flew up on deck or into the sails the sailors would catch them and get the cook to fry them. When a new cask of salt beef was opened the steward had first pick of the cuts for the cabin. What was left would be soaked in the “harness –cask” to get the salt off. Particularly tough pieces of meat were called “old horse.” Harlow includes the following rhyme that was sung each time a piece of “old horse” was found.

149 Water

There were two sources of water for the ship. First were the casks they brought with them which often became foul. Second, the crew would put out buckets during rainstorms. Water caught this way would be poured into the empty casks using a large funnel. Harlow considered re-filling the casks a very disagreeable job. He believed that because the cask funnel was too high it was impossible to fill the casks without getting soaked.

166 The crew was served a special “Cape Cod Turkey” for Christmas.

Cape Cod turkey is salt fish. Salt fish and plain duff comprised the sailors Christmas meal. This caused some grumbling. Evidently the men were accustomed to better fare on Christmas at least. “After clearing up the decks from the accustomed wash-down in the morning there was no further work for the day. Our Christmas dinner consisted of plain duff and turkey (Cape Cod)* which of course brought a big growl from the forecastle, with many comparisons with the Astor House, and this, with Hans in the lazaret, put the men in a state of unrest as they had nothing to do but growl.” *Salt fish”

173 Fred Harlow often went forward in his spare time to try and catch some of the fish riding the Akbar’s bow wake.

Fred found there were Dolphin [Mahi-Mahi presumably], Albacore, and Bonito riding the ship’s bow wake. Using a line he fished off the bow to catch them. If he was successful he would pull the fish up and another sailor would collect it in a gunny sack. A large fish could feed the entire crew.

187 A fish had bitten off Fred’s hook the last time he went fishing so the second mate rigged a make shift harpoon and caught a dolphin fish.

After a few tries the second mate successfully harpooned one of the fish which was put in a gunny sack. The cook however, refused to cook it, claiming the dolphin were poisonous. The mate told him to cook it anyways and put a coin in the water with the fish. If the coin turned green it was poisonous, if not it was fine. The coin did not turn green. Harlow felt the Dolphin was much tastier than albacore.

195 Tired of poor food, the crew confronted the cook

“About the middle of February our potatoes began to feel the effects of the damp, chilly weather. Having been wet with salt water they began to sweat and decay and grew so strong and sour that we couldn't eat them. At last the men went in a body to the cook and told him if any more sour spuds were cooked for the fo'c'sle they would send them back; also, that he must "lay off" the duff he had been send ing for they were tired of it and wanted a change. The cook was getting so lazy that he hadn't been baking bread for the crew, as it was much easier for him to throw a mess of flour into a sack and boil it, so we had been getting duff instead of soft-tack. The talk had its effect and we were given fresh bread for supper.”

311 In Java the crew secured tropical fruits to expand their diet.

“Alligator pears or custard apples were very palatable. The outer shell resembled that of an alligator—a hard, bristly shell of brown green, growing as large as four or five inches in diameter, but when opened containing a yellowish, cream- colored custard, with a few black seeds about the size of a hazel-nut meat. It was usually eaten with a spoon, but we sailors "got outside of it" without wasting any time. After shovelling coal all the forenoon there was nothing quite so refreshing as the green cocoanut at noon when we came on deck. Boring a hole through the eye we drank the milk which resembled water more than milk and it quenched our thirst better than anything else. After drinking the milk we cut the nut in half and ate the inside with a spoon for the meat had not formed and was very cool and refreshing. But of all the tropical fruit the little silver or sugar bananas, which were about the size of one's fingers, when peeled, stayed by us better than anything else ; perhaps on account of the cost, for with a gilder (about forty cents) we could buy a whole bunch. There was no trouble in getting fresh fruit daily, for the natives came off in bum-boats to sell almost anything that could be bought with money. One had to be an expert Jew to buy, for with plenty of time you could save half the price asked at first.”

311 When the Akbar was harbored in Java it was swarmed by bum boats.

Bum boats selling fruit and carrying prostitutes came up to Akbar in the harbor. They specifically targeted new arrivals that had money and had not had a chance to spend it yet. The sailors were not allowed by their officers to hire the prostitutes but they bought a great deal of fruit.

314 Loading coal was thirsty work. The Captain ordered oatmeal stirred into the water.

“The oatmeal water was quite palatable and I found myself going to the bucket every little while, until the second mate warned me that I was drinking too much and told me to put a small piece of coal in my mouth. My tongue rolling around the coal would cause the saliva to flow and I found that the roof of my mouth was not so dry nor did I require so much water.”

That about covers what one long distance vessel ate going to and from Australia in 1876. I realize this is doesn't address your question about whalers exactly, but I don't think the food conditions would have been overwhelmingly different. The main difference would have been fewer opportunities to resupply so there would probably have been more ships biscuit.