The Boat might feel familiar if you've done crunch variations. It's arguably more difficult, though, if you focus on form and not just scorching the core. To get there, sit with the knees and ankles together, then lift your legs and arms into a V position. Hold for five to 15 breaths and repeat three times. We've always found it difficult to know if we're balancing on the right part of the seat: What you're aiming for is the triangle formed by your sit bones (the bones that support you on a bike saddle) and tailbone.
The important thing with the boat is to keep your back long and straight, strengthening the core and the hip flexors, which are hard to target but get hammered during runs.
Benefits: Improves posture, helps prevent injury.