Couple things to keep in mind on a tuna trip.
Your fishing off shore and even though you should be fishing relatively close to other guys in your group, communication out there is by line of sight with your vhf since there's not cell service. With the rolling swells that are common off shore line of site to other boats isn't always the greatest so you may find even the vhf reception gets not too great at times. For this issue we bring a satellite phone. I highly recommended that at least one boat in the group of boats your going with has one. You never know when an emergency will happen and the Sat phone might be the only way you can communicate to someone.
When you're off shore you might be fishing in the freighter shipping lanes. Even though they have radar etc they are at times running on auto pilot. It's up to you to keep out of the way of the large commercial vessels. A radar reflector on a mast is a good idea for off shore especially on the glass boats.
Make sure your kickers are working well in case your main breaks down. A tow in from 40 to 70 miles out is gonna be nasty and dangerous for everyone. Bring tow ropes. Dont count on other boats to have them on hand.
Make sure you have all the safety gear.
Communication and sharing info is key with the other boats your out there with. If the fish are there, there will be enough to go around for everyone so let others know your location and where your finding them.
Make sure your wash down is working well. It's a blood bath even when using the cans. Try to gill them while they are completely in the cans. And bring a brain spike for the heads.
The garbage cans and large coolers are great. As others said one for bleeding, one for slurry, and the cooler for packing. Key is to get the fish bled, killed and on ice as quickly as possible to keep the meat in prime shape.
Dont cut your fuel supply short. Make sure you have a large buffer of fuel more than what you think you'll use in the day. You might find yourself not only running way out to find them but then also travelling a lot more to stay on them or hunt them down if you lose the packs.
If you come across the commercial Tuna fleet dont F up their tacks and give them room. Last thing anyone wants is the commercial guys and rec guys to have a conflict over Tuna.
