To have a boat ready
Because of the crowd.
They would not
καὶ εἶπεν τοῖς μαθηταῖς αὐτοῦ ἵνα πλοιάριον προσκαρτερῇ αὐτῷ διὰ τὸν ὄχλον, ἵνα μὴ θλίβωσιν αὐτόν·
There is no exact parallel to this summary statement in the other synoptics, although Jesus and his disciples were quite often in a boat in Matthew. Mark indicated that Jesus told his disciples (καὶ εἶπεν τοῖς μαθηταῖς αὐτοῦ) to have a boat ready or waiting for him (ἵνα πλοιάριον προσκαρτερῇ αὐτῷ) because of the crowds (διὰ τὸν ὄχλον). He was afraid that they might crush him (ἵνα μὴ θλίβωσιν αὐτόν).