There's a wide variety of battery terminals used in this install, and none of them are designed for multiple connections, which in boats in the norm rather than the exception.
When attatching cable lugs to clamp bolts the usual failure mode is that
the terminal splits as you try to tighten the thing up well enough to
make a decent connection. The other technique is to stuff lots of wires
into the hole and tighten the screw down hard.
The screw then graunches the cable until is breaks and falls out of the
connector with the engine vibration.
Post type terminals are now relatively cheap and plentiful and should be the first choice.