In the other boat
To help them.
καὶ κατένευσαν τοῖς μετόχοις ἐν τῷ ἑτέρῳ πλοίῳ τοῦ ἐλθόντας συλλαβέσθαι αὐτοῖς· καὶ ἦλθαν, καὶ ἔπλησαν ἀμφότερα τὰ πλοῖα ὥστε βυθίζεσθαι αὐτά.
Luke said that Simon and his boat signaled for their partners (καὶ κατένευσαν τοῖς μετόχοις) in the other boat (ἐν τῷ ἑτέρῳ πλοίῳ) to come to help them (τοῦ ἐλθόντας συλλαβέσθαι αὐτοῖς). They came (καὶ ἦλθαν) and filled both boats (καὶ ἔπλησαν ἀμφότερα τὰ πλοῖα). Thus, they began to sink (ὥστε βυθίζεσθαι αὐτά). This is the only place where the haul of fish made the boats sink.