Kabalite gunboats - how to use them properly?

Hi guys. I'm playing DE quite long ago but I still don't get, how to gain profit from gunboats. I prefer to use Venoms in my troop section, and when I experimented with gunboats it always ended terribly.
So, how do you use them? How many do you take and, what is very important, in which lists?
Do you take splinter racks? Do you buy additional weapons?
Do you start on the table or in deep strike?
Of course I speak about competitive gaming, it is all clear with friendly lists.
Thanks in advance!

I do probably average 4-6 gunboats in a game. I just load them up with kabs with a splinter cannon. Give it splinter Wracks. As for the weapon I norm go half DL half Dizzy. Start on the table and make sure they are in cover. If you have to use a gunboat sideways to give another 2 cover. I never have a problem with them, I use the hit and run poke tactics myself.

A good mix is what really should be brought:

1-2 gunboats, I generally field the squads 10-strong, with no upgrades on the squad, give the raider a lance, racks and if points permit nightshields since I really don't care if this guy jinks (no impact on the passengers).
A raider or two if you're fielding grotesques
The rest of my transports are venoms - generally 2-3 more warrior squads w/ no equipment and occasionally a squad of incubi since I'm still loving the mini-character klaivex.

It has been said many times, but the key to dark eldar is to really understand threat ranges and how to maximize potential, and being able to think a game turn or two ahead really helps as well. With venom's, you're anti-infantry is effective from turn one on as you have an effective 48" range on your guns counting movement, however in gunboats this isn't the case, you really want to get into that 12" double-tap range to maximize your effectiveness - but of course, that puts you at risk of being counter charged so you need to ensure you're safe from template weapons and are able to do enough damage that you're mitigating any effects from a charge from dudes with krak grenades.

This means that your gunboats need to work in concert with each other, as each fully loaded boat will only force about 8 or 9 saves on an enemy with a toughness value.

I generally try to move into position turn one to be effective at AI shooting turn 2, using terrain to block LOS where possible and hopefully move 12" or less so that I'm able to bring the lances to bear (if not, c'est la vie). I hope to be in a position that turn 2 I'm able to move at combat speed to maximize rapidfire on an enemy squad. From there, it's all target priority. Use the gunboats first to cause as much damage as possible, then use the venom's to clean up, as due to their range, they should have more available targets