Very new to SUPs and wondering if they can catch open ocean swells. Anyone with experience in the SW of WA? Out in my boat pearling is a very real risk at times, so I would imagine a long thin board designed to do it might be able to coast for ages on some of the big swells travelling north of our Cape to Cape region.

Or is it just short, steep seas the DW boards travel well in?

The best swell period is about 5-8 seconds, the larger period swells travel much faster and will be difficult to catch, Down wind boards are designed for these short period wind waves.

But the longer the board the more you can catch ocean swell or the less wind assistance you will need
A good unlimited board today is not far off catching swell compared to an OC1 if it gives you a better idea.
Anything you can't catch with a ski will be out of the question obviously.
So just by looking at ski and outrigger paddlers around your place will give you a good idea