One of the few things that is fairly well known about the ship class (another blog posting will have to deal with the shifting use of the name) Liburna/Liburnica is that it meant a fast ship from its origin until the 2nd century AD.

Appian, the 2nd century historian, describes their origin in the introduction to his book about the Illyrian War.

The Liburni, another Illyrian tribe, were next to the Ardiaei as a nautical people. These committed piracy in the Adriatic Sea and islands with their light, fast-sailing pinnaces, from which circumstance the Romans to this day call their own light, pointed biremes liburnicas.

(Appian, Illyrian Wars, 3. I've changed swift to pointed, following Morrison, 'Hellenistic Oared Warships' in Age of the Galley, 72)

Liburnae remained relatively fast ships, cruising ahead of the main fleet or pursuing fleeing enemy ships. To that end, they were sleek and as Appian says, pointed, ie. had a ram.

How fast was fast? Sadly, we don't know. Unlike the trireme, there are no specific examples of timed trips such as the famous race to Mytilene. But there is one episode that may, possibly, potentially, tentatively (yeah, I'm not convinced of its immediate value) provide some indication. It is also hands down, in my opion, the coolest testimonial of warship speed. It can be found in Virgil's Aeneid, not usually the go-to source for naval warfare, book V. The relevant part is quoted below from the Internet Classics Archive (the Perseus project was unuseable...). And for the dedicated crew, here is the Latin text.

Aeneas, having arrived back in Italy after a storm, decides to hold games in his father's honor. Part of those games is a race of warships.

Four galleys first, which equal rowers bear,
Advancing, in the wat'ry lists appear.
The speedy Dolphin, that outstrips the wind,
Bore Mnestheus, author of the Memmian kind:
Gyas the vast Chimaera's bulk commands,
Which rising, like a tow'ring city stands;
Three Trojans tug at ev'ry lab'ring oar;
Three banks in three degrees the sailors bore;
Beneath their sturdy strokes the billows roar.
Sergesthus, who began the Sergian race,
In the great Centaur took the leading place;
Cloanthus on the sea-green Scylla stood,
From whom Cluentius draws his Trojan blood.
Far in the sea, against the foaming shore,
There stands a rock: the raging billows roar
Above his head in storms; but, when 't is clear,
Uncurl their ridgy backs, and at his foot appear.
In peace below the gentle waters run;
The cormorants above lie basking in the sun.
On this the hero fix'd an oak in sight,
The mark to guide the mariners aright.
To bear with this, the seamen stretch their oars;
Then round the rock they steer, and seek the former shores.
The lots decide their place. Above the rest,
Each leader shining in his Tyrian vest;
The common crew with wreaths of poplar boughs
Their temples crown, and shade their sweaty brows:
Besmear'd with oil, their naked shoulders shine.
All take their seats, and wait the sounding sign:
They gripe their oars; and ev'ry panting breast
Is rais'd by turns with hope, by turns with fear depress'd.
The clangor of the trumpet gives the sign;
At once they start, advancing in a line:
With shouts the sailors rend the starry skies;
Lash'd with their oars, the smoky billows rise;
Sparkles the briny main, and the vex'd ocean fries.
Exact in time, with equal strokes they row:
At once the brushing oars and brazen prow
Dash up the sandy waves, and ope the depths below.
Not fiery coursers, in a chariot race,
Invade the field with half so swift a pace;
Not the fierce driver with more fury lends
The sounding lash, and, ere the stroke descends,
Low to the wheels his pliant body bends.
The partial crowd their hopes and fears divide,
And aid with eager shouts the favor'd side.
Cries, murmurs, clamors, with a mixing sound,
From woods to woods, from hills to hills rebound.
Amidst the loud applauses of the shore,
Gyas outstripp'd the rest, and sprung before:
Cloanthus, better mann'd, pursued him fast,
But his o'er-masted galley check'd his haste.
The Centaur and the Dolphin brush the brine
With equal oars, advancing in a line;
And now the mighty Centaur seems to lead,
And now the speedy Dolphin gets ahead;
Now board to board the rival vessels row,
The billows lave the skies, and ocean groans below.
They reach'd the mark. Proud Gyas and his train
In triumph rode, the victors of the main;
But, steering round, he charg'd his pilot stand
More close to shore, and skim along the sand-
"Let others bear to sea!" Menoetes heard;
But secret shelves too cautiously he fear'd,
And, fearing, sought the deep; and still aloof he steer'd.
With louder cries the captain call'd again:
"Bear to the rocky shore, and shun the main."
He spoke, and, speaking, at his stern he saw
The bold Cloanthus near the shelvings draw.
Betwixt the mark and him the Scylla stood,
And in a closer compass plow'd the flood.
He pass'd the mark; and, wheeling, got before:
Gyas blasphem'd the gods, devoutly swore,
Cried out for anger, and his hair he tore.
Mindless of others' lives (so high was grown
His rising rage) and careless of his own,
The trembling dotard to the deck he drew;
Then hoisted up, and overboard he threw:
This done, he seiz'd the helm; his fellows cheer'd,
Turn'd short upon the shelfs, and madly steer'd.
Hardly his head the plunging pilot rears,
Clogg'd with his clothes, and cumber'd with his years:
Now dropping wet, he climbs the cliff with pain.
The crowd, that saw him fall and float again,
Shout from the distant shore; and loudly laugh'd,
To see his heaving breast disgorge the briny draught.
The following Centaur, and the Dolphin's crew,
Their vanish'd hopes of victory renew;
While Gyas lags, they kindle in the race,
To reach the mark. Sergesthus takes the place;
Mnestheus pursues; and while around they wind,
Comes up, not half his galley's length behind;
Then, on the deck, amidst his mates appear'd,
And thus their drooping courage he cheer'd:
"My friends, and Hector's followers heretofore,
Exert your vigor; tug the lab'ring oar;
Stretch to your strokes, my still unconquer'd crew,
Whom from the flaming walls of Troy I drew.
In this, our common int'rest, let me find
That strength of hand, that courage of the mind,
As when you stemm'd the strong Malean flood,
And o'er the Syrtes' broken billows row'd.
I seek not now the foremost palm to gain;
Tho' yet- but, ah! that haughty wish is vain!
Let those enjoy it whom the gods ordain.
But to be last, the lags of all the race!-
Redeem yourselves and me from that disgrace."
Now, one and all, they tug amain; they row
At the full stretch, and shake the brazen prow.
The sea beneath 'em sinks; their lab'ring sides
Are swell'd, and sweat runs gutt'ring down in tides.
Chance aids their daring with unhop'd success;
Sergesthus, eager with his beak to press
Betwixt the rival galley and the rock,
Shuts up th' unwieldly Centaur in the lock.
The vessel struck; and, with the dreadful shock,
Her oars she shiver'd, and her head she broke.
The trembling rowers from their banks arise,
And, anxious for themselves, renounce the prize.
With iron poles they heave her off the shores,
And gather from the sea their floating oars.
The crew of Mnestheus, with elated minds,
Urge their success, and call the willing winds;
Then ply their oars, and cut their liquid way
In larger compass on the roomy sea.
As, when the dove her rocky hold forsakes,
Rous'd in a fright, her sounding wings she shakes;
The cavern rings with clatt'ring; out she flies,
And leaves her callow care, and cleaves the skies:
At first she flutters; but at length she springs
To smoother flight, and shoots upon her wings:
So Mnestheus in the Dolphin cuts the sea;
And, flying with a force, that force assists his way.
Sergesthus in the Centaur soon he pass'd,
Wedg'd in the rocky shoals, and sticking fast.
In vain the victor he with cries implores,
And practices to row with shatter'd oars.
Then Mnestheus bears with Gyas, and outflies:
The ship, without a pilot, yields the prize.
Unvanquish'd Scylla now alone remains;
Her he pursues, and all his vigor strains.
Shouts from the fav'ring multitude arise;
Applauding Echo to the shouts replies;
Shouts, wishes, and applause run rattling thro' the skies.
These clamors with disdain the Scylla heard,
Much grudg'd the praise, but more the robb'd reward:
Resolv'd to hold their own, they mend their pace,
All obstinate to die, or gain the race.
Rais'd with success, the Dolphin swiftly ran;
For they can conquer, who believe they can.
Both urge their oars, and fortune both supplies,
And both perhaps had shar'd an equal prize;
When to the seas Cloanthus holds his hands,
And succor from the wat'ry pow'rs demands:
"Gods of the liquid realms, on which I row!
If, giv'n by you, the laurel bind my brow,
Assist to make me guilty of my vow!
A snow-white bull shall on your shore be slain;
His offer'd entrails cast into the main,
And ruddy wine, from golden goblets thrown,
Your grateful gift and my return shall own."
The choir of nymphs, and Phorcus, from below,
With virgin Panopea, heard his vow;
And old Portunus, with his breadth of hand,
Push'd on, and sped the galley to the land.
Swift as a shaft, or winged wind, she flies,
And, darting to the port, obtains the prize. 

Virgil, Aeneid V.114-243

Ok, perhaps that quote was a bit long. But it's interesting if we could make out what kinds of ship Virgil is talking about here. Luckily it's been done before by Morrison in the same book referred to above. There are four ships, each given some words to describe them:

• Pristis (in the Latin text)/Dolphin, under Menestheus, is described as swift and fast.
• Chimaera under Gyas is bigger (vast bulk), and clearly a fast trireme, taking off faster than anyone else
• Centaur, Sergestus' ship, is great and mighty
• Scylla of Cloanthus is sea-green, better oared (melior remis), but heavier than Chimaera which it pursues.

We can agree with Morrison that Chimaera is the fast trireme. It is obvious from other sources that this type of ship had the best power/weight ratio and, when its hull was clean and dry, would be expected to accelerate faster than anything else afloat. Centaur is obviously bigger than the rest, a 'four' or 'five'. What about Scylla? Is it bigger than a trireme, or a heavy trireme as Morrison suggests? Should 'better oared' be interpreted as having a more experienced, stronger crew, or is there some technical feature about this ship that improved its rowing qualities (I wouldn't know of any possibility there), or is it a 'four' perhaps, and Centaur a 'five'? Pristis/Dolphin then. Morrison thinks that was a liburna, which may be reasonable. The author points out that Pristis is a name used elsewhere for lemboi (another related type) with a ram. I would add that Virgil is clearly anachronistic when it comes to ship types. If he's referring to his own time, then this could well be an imagined (or not?) race between warships of the Italian fleets of the era. Their inventory went from liburnae, to threes, quite a few fours and some fives. It would then be logical to identify the Pristis as the liburna here.

So what about the Liburna's speed? If (insert a few extra 'if's here) we take Virgil's race as an accurate representation of matters, then a Liburna was slightly slower than a heavy three or four, accelerated faster than a four/five, but might run out of steam versus the bigger ships when the race went on. The Centaur was a slow starter, but its large crew could perhaps keep a faster speed for a longer time. A liburna then was by comparison a bit underpowered, but light, manoeuverable and swift over fairly short distances, slowing down when it had to travel further. Can we put a speed in knots on it? That'll probably have to wait until we build and test one.