What makes a seaworthy boat is a very subjective thing.
Seaworthy is a relative term dependent on water conditions. You should have plenty of power to get up on step and plane quickly...you should have WEIGHT to your boat, beam is EXTREMELY IMPORTANT as well as deadrise, stability, freeboard etc.. Length is one component of that, in my opinion, you should have a sealed hull like a Whaler or Grady capable of self bailing/draining while under power. Fishing the banks 20 miles out? 22 footer minimum with self bailing cockpit...or be prepared for a very long ride back if you make the mistake of staying too long. Seaworthy is dependent on the safety of the vessel as well..twin engines or single? How fast does it move on auxiliary? How reliable is your power and boat systems? Do you have an ERPB? Do you have survival suits? Do you have radar or gps? Did you file an sailing plan? How much fuel does your boat have? How much fuel does your boat consume? All factors which are important. How fast your boat handle 5 foot seas 10 foot seas, 35 foot swells with seas?? What kinda interval between the waves? Some boats can handle having the crap pounded and slammed out of them on a hell run back to shore..others can't.
One of the other things is knowing how to drive your boat as well, to get the heck out of the rough stuff and through it to get back to shore faster. Some boats can move at 20 knots through slop water. Other boats, 10 knots. A BIG difference when time if of the essence.
All boats are not created equal..there are reasons why Boston Whalers cost money. There are reasons why Grady Whites cost money..and we're not talking "names" either.
There's a difference between "big" water and "dangerous" water as well.
At any rate, if you're inexperienced and stupid enough not to recognize when the weather is coming up and intensifying, then you're a fool to begin with. Usually one bad experience is all you should need to smarten you up if you're ignorant and arrogant, if you're lucky enough to survive, and if you make the same mistake again, you're really deserving---not that you weren't the first time.
Know your boat, know it's limitations. Know yourself, know your limitations. Boat and live within those limitations. Just cuz somebody else is there fishing, and seems unconcerned, means diddley..there's different limits for everyone. For example, a 30 foot Grady White with 500 horses off the back may be out there fishing comfortably, and have no problem flying back in on big water. Whereas a guy in a 21 foot Fishin' Machine with 200 hours would be begging for mercy....different situations entirely.
I can recall it blowing NW 25 knots off Langara, which makes for some big water, fishing off Langara Island on the Northwest Side for Springs. We were bottom fishing cuz the fishing was slow, and the boat I was in was very capable of handling the swells. Big boat, Big HP hanging off the back. We boated a 60 lb hali, I hog tied 'em and recommended it was time to head in. Not so fun when you have to think about what you're doing. The guests were comfortable so I put down some cut plugs off the downriggers, I could tell the weather was rising... and we spent about a half hour trolling in. We hooked a couple of 25 lbers, and then I suggested the "warm up" pit stop at the lodge and then a quiet evening fishing the tide at a favorite spot on the east side of island, calm, warm etc.. We hopped up on plane, and rode the 15 footers into the pass and back to the Lodge feeling very comfortable whereas everyone else (smaller boats) was to stay OFF the west side.
However, you really have to ask yourself. How much fun are you really going to have anyways putting yourself in that position? what kinda benefit are you really gaining? (none)
Answering questions like this REALLY should put it into perspective for you, and if you're putting in yourself into dangerous positions, you don't respect the sea, and it'll take your life. If you lost it because of that, hate to say it you deserve your predicament and fate. By the way, radios won't save you from sinking. The average response time for a helicopter, boat or search and rescue crew is far above what most people think, if you manage to get a mayday call through and they hear you.
By the way, if I think the weather is coming up you should be leaving WELL in advance, I'll stop and tell people on other boats I said so, and take them with me, or ask 'em if they're coming if not, I'll point that out. Oftentimes the suggestion is enough to wake 'em up.
By the way, you should NEVER be fishing out there in rising weather without a "buddy" boat. if they leave, you leave, if you leave, they leave. And you all leave together. That simple.