My advice would be not to eye-ball an installation like this, but to get professional advice from a yacht designer. I would think of several considerations for an inner forestay:
1. The loads of a storm jib
would be major, its more than a question of reinforcing the deck, the forestay fitting needs to have a bulkhead connected to the hull. On my boat the inner forestay is bolted/glassed into the aft partition of the anchor
locker formed by a stout bulkhead which isl glassed to both the desk and all the way to the V of the hull.
2. An important value of the inner forestay is to allow the storm jib
to prove airflow to the trysail/triple-reef main, so they work together. You typically see inner forestays located somewhere like 30% of J.
3. If you locate the inner forestay for proper use of a storm jib
, you aren't likey to be able to fly a genoa of any size on it, due the reduced hoist and LP.
4. the location of the top of the inner dforestay on the mast is another design question, as it will introduce loads that the mast may or may not be designed to carry. Some boat have runner setups to control the mast when using a second forestay, as often seen on fractional rigs