i just did a spicy beer and here's how i did it:
~1.7 oz fresh ginger peeled and grated
4 cinnamon sticks broken into bits
6 allspice berries lightly crushed
1 nutmeg seed grated
i put those in a tight mesh bag and put it into the boil 30 seconds before flame out. killed the gas, let it sit 10 minutes. pulled the bag out and let it drain as well as possible, tried to squeeze all the juice out before discarding the spices. after a week the ginger was really the only flavor i could detect in the beer
i have been told that 1-2 oz ginger is the recommended amount for a 5 gallon batch, 2 oz being particularly noticeable. 1 oz should still be noticeable, but if you only cut your ginger into pieces then maybe you didn't get a very good flavor extraction. i grated mine on a microplane and it basically turned into ginger paste. that was perfect.
25 minutes at a full boil could have done it too. i've never boiled spices, only steeped at knockout. you could let the spices steep in the boil for the last one or two minutes, but i don't usually let anything that will be flavoring my beer boil for very long. i'm not saying you can't boil your flavorings and get a good product, i'm just saying this is how i do it.