I have spliced a mast on a smaller boat and the local boatyard recently spliced a large catamaran
mast that broke a few feet off the deck
. From your pictures the break appears to be at the spreader, same as with my mast crack. The bolt going through the mast attaching the spreaders was loose resulting in an oval hole and stress cracks. Luckily we found the problem before the mast broke.
If you have a fractional rig then a splice at the spreader is not good. A bend in the mast of a fractional rig at the spreader does not go well with a splice.
If you have a full rig then splicing may work
. You will need to unstep the mast. Then trim the broken ends so that they are 90 degrees to the mast section. Measure how much length you have lost
. Then you will have to make an insert or have one made. Pieces of broken mast can sometimes be adapted to make an insert. If its the same profile as your mast, take a 4' piece, remove or slit inner sections and replace the track section with a slot. Then squeeze the piece using serious clamps so that you can insert it in one side of the mast. You will have to remove any inner sections in the mast for 2' in either direction. Then add thin epoxy to the outside of one half of the insert. Insert in a mast section and rivet in place using monel or stainless rivets (not aluminium rivets). Add an isolator such as tefgel and find a heavy duty pop riveter. Add tefgel to the end of the rivet as a glue to prevent the rivet rod from sliding around. Also preferably rivet from under rather than over the mast. Gravity helps the rod to drop down between riveter squeezes.
Once one side of the mast is done, push the insert into the other side of the mast. Make sure that the slot is aligned. Again use epoxy as glue and then rivet.
Make sure that the spreader attachment is sound and that it will not cause another break. If the attachment uses a through bolt create a sleeve with length being the mast diameter at the hole, for the bolt, so that tightening the bolt does not distort the mast.
The lost mast length due to trimming needs to be made up. This can be done by not fully inserting the sleeve and adding a band to strengthen the insert. This may already be needed to create a new spreader attachment.
Alternatively if the lost length is small, the stay turnbuckles may be able to take up the space as long as there is enough space between the sail head
plate and shive when the sail is hoisted. You may have to move the gooseneck down.
Adding a spacer under the mast could help if there is not enough stay turnbuckle adjustment but this will not solve the problem of the sail being too long.
So think of the ramifications of mast shortening due to trimming the ends. Find the cause of the mast break and inspect the mast carefully before starting. If there was one weakness, there maybe others.
I am not a professional rigger and this advice
should be carefully considered. The decision and responsibility is yours.