The arguments against a deck stepped mast that I have heard primarily go to a deck stepped mast with no support post, IE arch, or thickened deck to support the downforce of the mast. In these water intrusion of core material, or arch can weaken mast base to dangerous levels. Second more of a stub to rig makeshift mast, I'm not sure I follow that one, with a wooden mast maybe.
Not having tried to rig a makeshift mast on either types of boats, I'm not sure how it would work, but IF I had to I would start with using my cordless drill to drill holes in the base of whichever is longer, remains of mast, or boom, then attaching stainless screws to el brackets. With a keel stepped mast assuming you still have a cabin top, the mast will remain upright while you rig shrouds, but you will have a large hole left from the diameter change of original mast to makeshift mast.
With a deck stepped mast you would prerig shrouds first, then screw el-brackets to old plate on deck leaving your boat in original configuration with a shorter mast.
I my opinion is lashing a mast fragment to a stub of a mast would be an excercise in futility, try lashing two sticks together and then put a side load on them.
Generally speaking a keel stepped mast might be less vulnerable to dismasting, but a deck stepped mast would be easier to repair at sea, in both cases raising a mast in a rolling sea in a single masted vessel is going to be problematic.
I would say even in calm seas raising a mast of any size would be not only impossible, but extremely dangerous.
It may not be very seaman like for me, but if dismasted, and engine failed I would call for help, if dismasted and engine working, (or fixable), I would motor to nearest landmass.
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