Climbing the mast usually involves conning one of your friends to haul your heavy body up the spar so you can take a look at a few things. If you run out of friends who are willing to spend their day grinding on a winch, you will need to find a way up to the top and back to the deck in a safe manner alone.
One of the easiest and safest ways to climb the mast alone is to use a gantline. A gantline is a dedicated line that will raise a human up the mast. It is simple to rig and easy to use.
The gantline is made up of a pulley which is attached to a halyard. This pulley will be a double block. On your chair, you will have another block; double if you want to create a 4:1 system, or single if you want to create a 3:1 system. Between these two pulleys will run the gantline, which you will pull to raise yourself up the mast.
Some things to consider when choosing your system is how strong are you and how much do you weigh.
If you choose a 4:1 system, your weight will be divided by 4, but you will have to pull 4 times the height of your mast in rope to get yourself all the way to the top. If you weigh 200 pounds, and your mast is 50 feet tall, you will have to pull a weight of 50 pounds 200 feet. The weight is slight, but the distance is great and you will need a lot of endurance to make it all the way to the top.
If you choose a 3:1 system, your weight will be divided by 3, but you will only have to pull 3 times the height of your mast in rope to get yourself to the top. If you weight 200 pounds and your mast is 50 feet tall, you will have to pull a weight of 67 pounds 150 feet. The weight is slightly more, but the distance is vastly less. If you are strong enough, I highly recommend going with a smaller system, as you will get to the top faster and you will need less rope to do so.
The gantline is run through the blocks and tied off to the last block after all the pulleys are used. If you are using a 4:1 system, the knot will be on the top block. If you are using a 3:1 system, the knot will be on the bottom block. To go up, all you need to do is pull on the tail and you will slowly begin to ascend.
Coming down is easy too, as you let the line out, you will slowly descend. The friction from the pulleys will also cause you to come down a bit slower as well. If you loose your grip on the tail and begin to freefall, all you need to do is grab the mass of line that runs between the blocks and squeeze. The rope will stop moving and you will come to a stop without hitting the deck.
I like to use 3 strand nylon rope for my gantline because it is easy to grab and also easy to inspect the condition. Double braid rope can have a nice looking cover and a rotten core hiding below, waiting to fail while you are aloft. 3 lay is the entire rope, and what you see is what you have. If you notice severe chafe, you can easily identify it and repair it with a mending splice, or replace the entire rope if you do not feel comfortable with the idea of repairing rope.
Gantlines are a great method to raise yourself up the mast in a controlled and safe manner. They reduce the weigh involved which means that you can pull yourself and your tool bag up to the top of the mast with ease and peace of mind.