[Steely Jim]

Well, I am a little confused when you say you grabbed them but didn't grapple them. Did you shoot grappling lines at them and the ship was reeled in like you expected; but, you neither saw the grappling lines/hooks, nor got the board option? Or, could you see the grappling hooks/line extending to the other ship, but just never got the option to board?

In any case, I board the little Sentinel flagship off PDF with my frigate quite often. No special frigate tricks or anything, just shoot grappling lines at the green circles like from any other ship. I'd have to guess that if you're seeing the grappling lines, but not getting the "Board" pop-up menu, then it's some sort of bug. If you've boarded from other ship types, then you should be able to do the same from a frigate

Do you still own any other ships, and can you still board with any other ship? When you have other people on your frigate, are they seeing the board option after the ship is reeled in? You may want to try getting on the crew of someone else's frigate and see if anything changes before you report it to customer service.

EDIT: To follow up, I took my frigate out from PDF and boarded that EITC Sentinel. I did a full routine: brought it down with regular cannon balls, took out the masts and the pilot, and threw over some stink pots at the guys on their deck. Everything went normally, including firing the grappling hooks over and the timing of the pop-up "Board" menu.

EDIT2: I just boarded a Level-21 EITC Ironwall near Isla Perdida using my frigate, all 4 of the Level-11 Thugs found aboard were slain mercilessly, after their helmsman had been shot with a cannonball. I didn't have any trouble with the grappling or boarding process, so it's seeming more like a bug.