Bow thruster and plough: what they have in common

1. Step 1. Bow thruster — has part — Propeller. A propeller in a tunnel.
2. Step 2. Propeller — is part of — Icebreaker. Propellers.
3. Step 3. Icebreaker — uses — Wedge. The bow rides up onto the ice and crushes it.
4. Step 4. Wedge — is used in — Plough. The ploughshare parts the soil like a wedge.

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