does anyone now what the sailors of the royal navy ate in the 18th century / early 19th century?

Tim D is basically right.

N. A. M. Rodger in 'The Command of the Ocean' lists as standard supplies:

Bread, beer, brandy, rum, wine, beef, pork, peas, onions, flour, oatmeal, suet, cheese, raisins & other dried fruit, vinegar, oil. Citrus fruit/juice was increasingly carried to prevent scurvy. Dried cod had been phased out as it was unpopular with the men. A goat (for milk) was sometimes carried, as were beasts for slaughter. These together with the ship's poultry were kept forward in an area known as the manger.

One day a week was a 'banyan day' when no meat was served. The salt meat was usually dehydrated and rock-hard; it could, unless fresh in cask, be eaten only after stewing. The powerful onions carried lasted well, and in a stew helped both to tenderise the hard meat and to make the flavour acceptable. Contrary to common modern belief, rum was not always served. Sailors drank beer (the water soon became stale) and there was a daily allowance of stronger drink: white wine, brandy and schnapps are variously mentioned, and which was issued depended on where the ship had been able to victual.

The quantity was plentiful; fully ample for the hard-working life of a sailor of the period. However the menu was monotonous. Oatmeal porridge ('burgoo') was the standard breakfast. Dinner was almost invariably stewed meat with pea soup (mushy peas flavoured with the 'slush' or fat from the boiled meat) and onions. Sometimes there was a pudding ('duff') with dried fruit and sugar. Cheese was served most days, and as a main source of protein on a banyan day. Ships carried a trawl net, and when in shallow water the men would also fish (Spavens has an illustration showing this) to supplement the diet with fresh food.

Hope this helps.

Ship’s biscuits and salted meats supplemented with whatever local produce they could get. Salting was one of the few available methods of preserving meats. They would also carry livestock and hens to slaughter during a voyage but livestock takes space, food and water too so the lifespan of an animal taken on board was short.

Eventually lime juice became important as a source of vitamins to avoid scurvy, although limes were poorer in vitamin C compared to lemons, however the lemon-producing nations were mainly in a state of war with Britain and would not trade with the Royal Navy.

There is a recipe for ship’s biscuits here

http://en.wikibooks.org/wiki/Cookbook:Hard_Tack

Limes, hence the name Limey's for English Sailors and Englishmen in general. Most important discovery as far as diet on board ships of the time were concerned.

.

They were first to realize the connect between scurvy & rickets with a deficiency of vitamin C. Limes were high in Vitamin C. They didn't spoil fast, and they were small. They were also readily available in the tropics and sub-tropics.

They most likely did not know it was the vitamin C at the time. They knew that eating the limes would prevent their sailors from getting scurvy & rickets.

As for the other: You need to know they did not have any means of refrigeration back then. You also need to know about the only food preservative was salt in the period of time.

Also on board most ships space was at a premium then as it still is today on all but the Fast Capital ships of the Line like the HMS Victory. Or the larger 44 gun Frigates.

Speaking of Lord Admiral Nelson's Flag Ship the HMS Victory you need to take a trip to the Historical Shipyard in Plymouth and tour it when you get a chance. That will tell you more about the ships and living conditions on shipboard than any book of a 1,000 pages could do.

Due to lack of any way to refrigerate their food and lack of modern day food preservation technics they ate mainly:

Salted meat & dried meat. Beef jerky or common nickname hardtack.

Salted fish

grain in the form of wheat which was used to make bread

Rice was another staple when they could get it because it was not bad about spoiling.

Cheese Back then bread and Cheese was pretty much the main staple of the common folks anyway:

rum:

wine:

dried beans when available

corn when available & hominy since hominy would last longer shipboard.

When they was in port and just leaving port they'd have fresh vegetables for a few days out or as long as they kept.

Berries such as blue berries etc after people learned how to preserve food by canning.

vegetables which had been canned or preserved by canning again after they had learned how.

Preserves and jellies

After they had been at sea for a while what they ate mainly depended on what was available at their ports of call.

As for your big 104 gun fast First Ships of the Line and large 44 gun Frigates some of them carried live cattle, goats and chickens as well.

The cattle & goats were both for their milk and to butcher for their meat.

The chickens were for their eggs and to kill and eat as well.

Again a lot of what they ate was dictated by what they could purchase at the various ports they called on. Or what their landing parties could gather.

More or less you ate what you could get.