1 vet = 4 experts.

That said, you will burn through experts trying to get vets, and will need to refil experts (through various ways such as natural expert growth, crits, AA or purchasing). If you burn through all your experts for a handful of vets, your crews ability will be temporarily gimped until the experts are refilled/replaced.

yes you will i belive somethin like 10 vets is worth 30 experts

Do exp->vet conversions during events with increased conversion rates. Also some people say that doing conversions directly after the sailor leveled up is more successful, although I have never seen anyone providing a conclusive statistic for it.

Oh and you can also purchase vets and experts from other players. Some still have unused packs of those in their items. But I'd suggest to do that only with people you trust, because you'll have to lend them your sailors so that they can use their packs on them.

Very grateful for the help, have vetted all my sailors but took your advice and trying to do it slowly. Used a few packs I had got from events etc.

Any idea when these upgrade event things are? Or do they announce them?