I use the 5 mph wind=1 foot wave height. 15 mph= 3 foot wave. There are variables of course, islands, wind direction, etc.
My 18' Lund Tyee is great for 1-2.5 wave height. 3 foot waves make me uncomfortable, and hard to fish. Our class of boats (open bow) is added caution also.
Remember wind kicks up unexpectedly. I recently bought a bow cover for days of expected wind change.
I use Windfinder.com for info, seems to be very close to real deal.
Best chance of securing good wind is a day before you leave, checking weather. Not good for planning trips as discussed.
I'd rely on the charter captains weighing in on this subject, they have experienced it all. Stay safe.