Squid Tentacle are obstacles in Build A Boat For Treasure. They launch boats upward into the sky when touched, also making a sound. They also do loads of damage to your boat. This can make your boat stay in mid-air which can be annoying near the end. The tentacle represents the tentacle of a giant squid protruding from the water. You can also kill these with Cannons.
You can counter them by dodging them, using the pilot seat.