Marine lumber generally isn't selected for hardness. Generally speaking, rot resistance is the most desirable characteristic. Apparently greenheart is superio

Marine lumber generally isn't selected for hardness. Generally speaking, rot resistance is the most desirable characteristic. Apparently greenheart is superior to most other wood in this regard. Teak has traditionally been used for this reason as well, but is getting expensive. Black locust is starting to become popular as well. Apparently greenheart is relatively rare and prone to exploding when milling, however.