Your skipper probably has done enough fishing there (at least at his usual spots) to have the confidence to say that or place a bet. It is most probable that the skipper will not let you take the sailboat wherever you want unless you know him well and furthermore useless if you're not experienced in identifying and locating spots in the middle of the sea. You wouldn't want to waste time echo-sounding the seabed blindly as well.
If you're talking about landing a fish of any size, it shouldn't be too hard for any frequent angler. Just park near any reef (or rocky shores of St John's/Lazarus/Kusu) and fish on the fringes (where the corals slopes steep down into the depth), you'll almost certainly get some sort of fish if you have your fishing techniques right. However, reef fishing may not be suitable for sailboats as it often require you to anchor in shallow waters. Sailboats with short keels might be still able to do so but I doubt the skipper will be comfortable with it.
As to the "NO FISH to be had around this time of the year" statement, it is most likely an exaggeration. He probably meant that the catch wouldn't very good. Boaters and charters fish around there every week regardless of time of the year, so it is not likely that catches will definitely be poor or they would have saved themselves the trouble of coming out at all. No intention of offending any charter, but catch rate depends a lot the competence of the charter/guide. The skilled and experienced guides have lower chance of ending the day with a bad catch.
There are some truth when talking about lesser fish at certain time of the year, typically some species of fishes come into our water to spawn or brought in by ocean current drifts. I heard somewhere behind St John's Island is a good spot for catching Threadfins at certain time of the year. It is a pretty steep and deep drop-off. Where exactly I don't know.
I believe you'll most likely end up like all angler paying for a charter, just fish wherever the captain takes you. So what you can do on your part is pretty limited to your own angling skills and luck. However, the type of rigs and bait used can make a lot of difference. Manning your line vigilantly and checking bait timely increases your odds in landing a fish dramatically.
Using live prawns will cover the widest range of fishes that can be caught, whole squids (live/very fresh ones) are better for targeting biggies. For rigs, simply a long trace bottom rig will suffice especially if the boat is drifting. You can choose two use 2-hook Apollo if you can man your lines attentively. If you just want to land a small fish to prove to the skipper, you can always use 3-hook apollo (as small as tamban hooks) and use cut pieces of dead prawns.
Welcome to HLF, good luck on your upcoming trip.
I was debating between using prawn and using squid. not sure if prawn is good for anything in our waters other than Todak?
One small mullet/tamban/squid... anything.
