On the rare occasions where the learned Adept has need of explaining the workings of the Warp (aka. the Empyrean, aka. the Immaterium) to a layman he often resorts to using the parable of the ocean voyage: The ocean is the warp and instead of a ship sailing across the watery surface you have a voidship plunging through the great unknown. Solar systems get described as tiny islands in a dark and vast ocean. Navigation is difficult because clouds are almost always obscuring the stars, save the brightest star of the all - the Astronomican. Currents and storms can throw a ship of course - or sink it utterly. And the predators of the deep...the shark and the sea serpents and the leviathans...well, there be Daemons on the charts for a reason.

The Warp actually has very little in common with planetary oceans, but let's stick with it for lack of a better metaphor. But if we must use the ocean to explain the Warp, let us instead go under the surface. That adds dimensions to our tale that the surface of the ocean lacks. So...let the voidship be a submersible. The submersible is protected by a pressure hull. That hull is all that stands between its occupants and a watery grave. This hull very rarely loses integrity, but when it does the effect is spectacular: Sea-water gushes into the sub, flooding it. If the breach is large there is naught to be done; there is no escape for crew and passengers, and the vessel itself sinks to the bottom of the sea. If the breach is small, however, the crew might be able to stem the flow of water long enough to surface.

It's more or less the same with a voidship and its Geller field; the Geller field protects the ship - without it everyone dies a horrible death and the vessel is lost. There is no water involved of course; instead the Geller field maintains a bubble of normality around the ship. Without this bubble the full entropic effects of the Warp will grab hold of the ship and its occupants. Destruction is not far away. Even a small 'leak' in the field can create a lot of trouble; the weird energies of the Warp can do untold damage to a voidship, even if the Geller field doesn't collapse completely. And of course there are the Daemons...but that's another issue altogether.

Entering the Warp requires preparation, just as it does for a sub to go under the water. The Warp drive must be brought online and charged - which requires stupendous amounts of energy - and all manner of calculations and preparations are made before reality is finally rent asunder and the ship slips into the Empyrean. A sub doesn't require a Warp drive of course, just some ballast tanks, propulasion and adjustable planes - but the principle of preparation and readiness is the same, even if there is no tearing reality apart in the case of the sub. And just like the sub can't dive in shallow water the voidship cannot enter the Warp where there is a powerful gravity well nearby; gravity equals the shoals of the Warp if you will: Most ships need to be in a system's outer reaches before entering the Warp - the orbit of Saturn is considered the safe Warp threshold in the Sol system for example. Finally; where the sub creates bubbles and turbulence in the water as it dives, so too does the voidship create ripples and disturbances in the space-time continuum as the Warp drive engages. And when the transition has been made both types of ship are simply gone, leaving no trace of their existence behind.

Let's presume for a moment that you've got both the entry and exit strategies covered. That only leaves the actual journey. Which pretty much involves pointing your ship in the general direction of the star you're going to and pushing the 'Engage' button on the Warp drive control station. Right? Wrong. Very wrong. Navigating in the Warp is difficult; much worse than steering a submersible with nothing but the most rudimentary telemetry to work with. The ship's empyric augury arrays collect some data, which is sufficient to perceive the ship's immediate surroundings. Ships without Navigators use these data to navigate by running them through massive cogitator banks. It's not perfect, but it works for short trips. If the ship is fortunate enough to have a trained Navigator on board its ability to traverse the Warp improves dramatically; Navigators have a unique psychic capacity to perceive raw Warp-data without the need for additional machinery. Simply put they just peer into the augury arrays and their minds plot courses with far greater accuracy than a mere machine can accomplish. Needless to say Navigators are rarely completely sane...and many suffer from bodily mutation. Such is the price they pay for peering into the Warp for a living. The Astronomican is another important factor; if this beacon of Imperial might shines brightly Navigators can use it to fix their position: Much like ancient mariners used stellar formations fixed above the poles of their worlds to navigate by. If the light of the Emperor grows dim - or is obscured altogether - their ability to navigate (pardon the pun) is somewhat curtailed, but still significant.

For navigation to mean anything you have to know where you're going. That's when those tiny islands in the great, dark and often storm-tossed sea come in. Having a real-space bearing is a good starting point, but nowhere near sufficient to get you where you want to go: Once you go under the surface you'll lose you target and won't have more than a general idea of where you must go to reach it. Again Navigators and the Astronomican makes it a bit easier, but you're still essentially going blind. You'll need to resurface frequently to get your bearings, then dive again (with all the complexity entering and leaving the Warp entails). Repeat as often as needed. It works, but it can take months to reach even nearby stars, making large-scale interstellar civilizations...impractical. That's where Warp routes come in. Warp routes are paths through the warp that have been charted in detail, taking note of markers, currents, ebbs and flows or whatever they call it. Even in a realm of Chaotic energy there are patterns that offer a way of telling one place from another (but routes do change and need constant monitoring and updating for charts to stay viable). The houses of the Navis Nobilite guard the knowledge of such routes jealously: The greater the house the more routes they will know and the greater the extent of their travel networks - and the greater their power and wealth will be. Ships without Navigators also stick to the same routes; Chartist vessels have the data required to travel between their designated ports of call, but rarely more than that.

Once the course is set the ship's warp drive will be able to move it in the direction specified by the ship's navigator - be he at true Navigator or a mere man and his machines. The Warp is in constant turmoil, so regardless of the course laid in there will be a drift. The Navigator and the Helmsman will work diligently between them to keep a ship on its course, but there will always be some deviation, however slight. It's more a skill thing than a power thing: The Warp is rarely turbulent enough to actually force a ship along, despite its warp drives; it's far more common to be pushed ever so slightly off course. And remember what I said about dimensions - the Warp has very many, so it's tad bit more complex than up-down and north-south. Try keeping your bearing in seventeen dimensions, with drifts and flows and sheers in all of them and you'll know what I mean. But barring major turbulence or outright storms the ship will move where its Captain wills.

Then there is speed. Speed is generally taken to mean time used to cover a distance. Well, in the Warp both time and distance cease to behave in a fashion that's predictable, so already the 'speed' thing gets a little murky. But as a general rule the deeper you go the faster you move. I don't have a good ocean metaphor for that one, except perhaps if the core of the world was filled with watery tunnels and you could move through them and reach the other side faster than you would if you had to traverse the surface ocean. In the Warp it's more about how many dimensions you're willing to play with; deeper essentially means taking on more dimensions and using them for travel. The more dimensions are involved the greater the complexity of navigation...and consequently the risk of getting lost - possibly forever - increases dramatically. Which is why a ship that has a Navigator who can see the Astronomican it can make longer journeys at greater speed; they can go deeper, faster, without risking destruction. Lesser Chartist captains who must do without such luxuries can only move between local systems at a much slower pace. As a side note lesser charts need only contain a fraction of the data complete Navis Nobilite charts holds, because the Chartist barges using them will never go that deep.

Finally your destination island is looming ahead of you. Then there is getting to the surface...unfortunately leaving the warp is not as simple as pushing a big red button or pulling a panic lever. Cutting the warp drive just leaves you adrift on the currents of the Immaterium; it doesn't return you to real space. So not only is it pointless in terms of getting out, it will actually throw you off course - which is never a good thing. Disengaging the Geller field also doesn't work, but it's infinitely more stupid: It's not the field that's keeping you in the Warp - it's whats keeping the Warp out of you! Losing the Geller field is like breaching the pressure hull of the sub; the outside comes rushing in to fill the vessel., which is a very, very Bad Thing! One final solution that doesn't work: Supposing you're close to a solar system you might think that heading in-system will yank you out of the warp once you're deep enough in the gravity well. That works about one time in a million; the rest of the time it's like running your sub at full speed into submerged reefs just off the coast of the island you're trying to reach...'Total Warp breach imminent'...those are the last words you'll ever hear, droning out from the ship's intercom system.

To leave the warp you first have to ascend to the surface - remember we're using the submarine metaphor - before you can break through into the air.This is one point where the metaphor fails to convey the message: The warp is not an ocean. It doesn't have just three dimensions; it has many, many more. Even with a Navigator on board it might not even be apparent which way is 'up'. The difficulty increases if the ship's aethyric auspexes are damaged or local warp conditions makes navigation difficult. Then there are Warp storms; not only can the push you of course, but they can be a real show-stopper for those trying to escape the Warp: As you near the surface the risk of destruction rises many-fold, as the storm gains in destructive power as you draw closer to reality. Not unlike the effects of a real-ocean storm; you can ride the waves when out at sea, but once you get close to land things suddenly get more dramatic and dangerous. Thus most ships will just have to risk riding out the storm - which will likely leave them wildly of course.

Now that you sub has finally reached the surface there is another problem; the sea is covered by a thick sheet of ice. Unless you can find a suitable spot for breaking through you're going to be stuck down there. Fortunately - unlike the sub - the voidship as an advantage; it has a Warp drive than can rip open a hole in the icy surface of reality and let it slip back into real space. Congratulations - you've made it to your destination. One final thing remains; getting a fix on the current real-space time. Time in the warp gets compressed at variable rates (generally speaking greater the deeper - faster - you go). For a slow Chartist vessel the compression ration could be as low as 1:2 one week of ship-time for ever two weeks in real space - but for the fast Nobilite highliners it could regularily go as far as 1:5 or greater. As a result ship crews tend to outlive any on-world relations that they might have, further setting them apart from the land-based kin.

Communication needs mentioning: It's perfectly possible for a vessel in the Warp to send and receive astropathic messages. Caveats do apply; the deeper in the Warp the harder it is for astropaths to send and receive. Turbulence and storms can also disrupt communications; but that's not unique to vessels under Warp drive. Most Astropaths - and Captains for that matter - are rather reluctant when it comes to communicating: The uneducated think it's asscociated with 'bad luck'. Those in the know are aware of the possibility of a ship attracting the attention of aethyric predators and the strain that can place upon a ship's Geller field. Reception of messages is perhaps less dangerous, but it is still not to be undertaken lightly: There is always the chance of insanity, psychic backlash or even bodily entropy. To be fair the danger is there in real space as well, but aestimates indicate that the frequency of incidents go up while under Warp drive - and that the average magnitude of at-warp incidents is much greater. If as ship must communicate it will generally rise close to the surface before transmitting.

One final thing: It is possible for ships in the Warp to detect one another. The chance is very slight, but it is there: Geller bubbles are at most a few hundred kilometers across; they are less detectable than a single snow-flake caught in a roaring blizzard. Powerful augury arrays help of course, as does having an idea as to the location of the other vessel and where it might be headed. Navigators are another great asset in this regard as they can interpret Warp data more accurately than servitor operators; some skilled Navigators can even track the paths of other vessels through the Warp with some accuracy. Since ships can detect one another they can engage one another as well; combat within the Warp is rare because detection chances are so low - and because when it does happen it is a brutal, short-range affair: Geller bubbles must overlap, meaning ranges are a few hundred kilometers at most - practically point-blank range in terms of space combat. That's too close for torpedoes to arm or lances to target properly, meaning that it's usually down to battery fire. Furthermore void shields cannot be brought up to strength because of the power drain of the Geller field, so ships are protected solely by armor. Needless to say few sane captains are willing to risk entering into combat on those terms.