I have an old Ideal windlass that appears to have a wildcat for 3/8" BBB. THe
boat came with 5/16 G40 which does not quite strip off right.
This is understandable as that the
pitch (inside length of link) are a bit off.
Interestingly, 5/16 G70 feeds and strips much better...
3/8" BBB has an inside length of 1.09", 5/16 G43 1.03 and 5/16 G70 1.12.
A cogs on the windlass engage every other link so the actual edge to edge
pitch on the windlass is twice the links inside length (inside length - wire dia + inside length length + wire dia = 2 x inside length)
SO for 3/8" BBB we get a windlass pitch of 2.18" for 5/16 G43 we get 2.06" and for 5/16 G70 we get 2.24.
Clearly being a bit too long is better than being a bit too short. You can take up the slack and snap into the slot rather than riding over because you are under tension.
Using those numbers above I find that compared to 3/8" BBB, 5/16 G43 is 5.5 % too short and 5/16 G70 is 2.8 % too long.
As I said I put 5/16 G70 on my
boat. I fed the entire 275' into the chain locker and did not see any bindings, overrides or failures to strip.
The numbers above are from direct measurements of chain that I had in hand with a digital caliper. One of our local chandlers has sections of chain that you can borrow to try out on your windlass. I should note that in measuring those chain sections I found that one was mislabeled. (measurements don't lie)
West
marine cut me off a section of 5/16" G70 for free so that I could test it in my windlass. (gotta love WM for all their faults)
If there is any suggestion it would be to locate a windlass that takes 3/8" BBB and try a section of 5/16 G70 to see how it fits.
Regards
I should note that these numbers were measured with Acco chain in the local West
Marine.
Also, the G43 spec quoted is for iso chain. Regular length is speced at 1.15" and may
work....