Hello. Here some ways to use more galleys. It can be useful.
1-Use more galleys for the galley trick. If you have more galleys, you can collect more resources from raids. But the cities must have a lot of resources first to raid. Upgrade harbor too. Use GPS to upgrade capacity too.
2-Use more galleys to trade more resources at one time quickly. Especially good to trade with friends.
3-Use more galleys to store resources. You can make a trade offer. But set the trade offer price only at very good price for you. For example, you offer 40k food for 80k wood. Most players will not trade that. If they do, you win. But if they do not trade, you can store the extra resource in the galleys. This is like a protection. Your acropolis can only protect some of the resources. The galleys can protect more of your resources.
Good luck