Simple.
Discuss it with the skipper when booking.
Not sure I understand why the need to discuss here?
Personally I really dont think it could be any simpler.
"Hey skip, if we book you can we have a 14 hour trip?"
Answer = Yes or No
"Hey Skip, if we book you for an 8 hour trip and we are having a good day, can we keep an option open to extend it to a 14 hour trip?"
Answer = Yes or No
If yes, then book the trip, if No, then thanks but will find another boat.
Many of us will book spaces as individuals, rather than the whole boat. In that case it is rather more difficult to influence the duration of the trip.
It is true that, very occasionally, a wrecking trip will produce more than enough fish in a couple of hours. Also there is the odd occasion when no fish whatsoever come to the boat. More typical is that 4-5 hours fishing will produce a couple of fish.
The cost of the boat is only part of the overall cost of the trip. I live a fair way from the coast, driving to the boat will take 1.5-3hrs depending on port and cost ÂŁ20-40. There is then the cost of food for the day an the inevitable lost tackle plus parking adding ÂŁ10-20 extra.
All in I suspect I rarely have change out of ÂŁ100 per trip.
On a typical 8-9 hr Wrecking trip, the time fishing, therefore, costs me ÂŁ25 per hour.
If the trip length was increased by 4 hours for, say, another ÂŁ20 I would get twice as much fishing time for not much extra money - reducing cost per hour to cÂŁ15
I do also like the idea of being able to try a few different things rather than just wrecking. For example the Turbot that have been found far offshore. I've heard mention of a couple of other offshore options that would be good fun but out of the range of a normal 8-9 hr trip.
In short, yes, if Sussex skippers offered 12 hour trips for ÂŁ75 ish I would definitely book.
Further west longer trips are quite commonly offered, but I would rather use ports closer to home.
I did go on a 15hr trip out of Weymouth last summer. I was great, we got the best of the tide ebb and flow for wreck drifting, some time at anchor for congers and a couple of hours flatty fishing on the way in. Best part of 11 hrs fishing time for ÂŁ85 felt like a bargain to me!.
I would have thought a few of these trips would be attractive to skippers. Whilst the longer day will burn some extra fuel and be knackering if done too often, it is a chance to break from the normal routine, get some publicity for doing something different - and probably end the day with more profit even once the extra fuel is covered.