If you want to build a kayak, the best structure is sitka spruce. It is both strong and light. Once the boat is built, varnish everything exposed. Red Oak is not a good boat building wood. Although it is initially strong, it needs to be thoroughly sealed to keep moisture from penetrating and encouraging the growth of fungus. Its cell structure encourages the retention of water.

If you wish to test this for yourself, put your mouth on the endgrain of a piece of red oak {Make sure it is not treated with antifungal poisons, first!] and blow through it. Then try the same with white oak. There really is a difference.

Ash is strong but it is heavy and soaks up water like mad unless it is properly sealed. It is easier to get oak or spruce.