Coincidentally I just helped my son in law sort out new chain for the identical windlass. And I used the same chains you mention in the gypsy on my sailbot.
When researching new chain for my boat
, after a few hours of research
, including calls to chain companies and emails to SL engineer
I learned that the most critical spec for chain to work in a windlass is the number of links per foot OR the inside length of each link which determines the number of links per foot.
3/8" BBB and 5/16 G4 are almost identical in this spec and should work interchangeably in your windlass. In fact just to check I took samples of both and laid them in son in law's windlass and both fit snugly in the gypsy.
On my boat I had planned to replace the old 3/8" BBB with 5/16 G4 but got a super deal on new 3/8 so stuck that. However the spare anchor
with rope rode
has 25' of 5/16 G4 that works perfectly as well as the 3/8 BBB in my Simpson Lawrence