I have never gaffed a halibut, but I have gaffed a lot of grouper, amberjack and king mackerel up to 40 pounds. The idea of a gaff is to bring the fish on the boat as quickly as possible. I usually have the point facing up and hit from below the fish to put weight on the gaff as quickly as possible. I aim for right behind the head. You usually miss short and aiming for behind the head usually put the hook in the head if I miss. Then I yank the fish into the boat. You then either wait for the fish to stop flopping or expedite the process by hitting it on the head until it stops moving. I assume you are using 50lb gear. If so, you will only need to gaff large fish (>20lbs) or fish barely hooked. Just swing the small ones right in the boat or cooler or use a net. One thing to remember is to have the person fighting the fish take tension off the line right after you gaff the fish. Sometime the hook can come loose or mono break which sets lead and hooks into motion. Very dangerous.