There is a free ferry from the Central Station (A) to the Botel (B): the NDSM shipyard ferry. This ferry can be found behind the station on the River IJ. The trip takes about 10 minutes. The ferry does not run at night. Instead, there is a free shuttle bus that runs between the Amstel Botel and an other ferry who brings you to Central Station.
On the A10 ring road take the exit S118 (A) towards Tuindorp-Oostzaan. At the crossroads go left; then at the traffic lights turn right into Molenaarsweg. Molenaarsweg becomes Cornelis Douwesweg. After two roundabouts go straight over the traffic lights into Klaprozenweg. Take the first road on the right (Van Riemsdijkweg). Carry on towards the water to the NDSM pier and the Botel (B).
Schiphol has its own, underground station. You can take any train that goes to Amsterdam Central Station. There you can take the ferry from Central Station, as described above.
The Entire Botel