BLUEMOMENT

Stealing a theme from a post by NickB...
"If you are fitting a removeable inner forestay then I believe.... You will have to ensure that the through-deck fitting is able to stand the considerable forces involved."

Right. Agreed. And I'm in process of doing that. Or planning to do just that....
Of those who have done such a thing, what 'zackly did you do re said 'beefing up' and was it enough?

there is a u-bolt on my foredeck, just aft of the chain locker. I strengthened it to take the load of an inner forestay by fabricating a s/steel "L" shaped bracket. the long leg of the L is bolted to the bulkhead and then the u bolt is bolted through the aft facing shorter leg of the L. this spreads the load on the deck (like a much larger washer) and transfers the load to the bulkhead.
if you're up near Craobh sometime, I can show it to you

On my own boat the inner forestay, a retrofit item, is no more than a U bolt with a small backing plate under it. Its been that way for decades, since before I purchased the boat, but is likely the less suitable method of backing.

On some Rivals, the design by Peter Brett, is an ply arch that runs under the bulkhead and curves down each side to tie into the hull by about 9". The arch is bonded onto the deck and hull and the chainplate is secured to that.

On Hallberg-Rassy's, at least one model, uses a stainless flat bar that is mounted to a clevis plate on the inside of the bow / fore cabin and rises up and penetrates the deck through a slot. The end of the bar has the hole for the inner forestay to be attached to. The hole in the deck is filled with a sealant and capped with a stainless cover plate. I think this is a very secure way of mounting an inner forestay without stressing the deck.

I have also sailed on a boat that had a stay in the fore cabin. It was connected to the bottom of the inner forestay chain plate and to another chain plate on the inside of the bow and was tensioned with a bottle screw. I am thinking of using this to upgrade my own inner forestay mount but would use a high-field lever. The advantage is that it can be removed when in port to allow the fore cabin berth to be used as a double without the restriction of a stay bisecting the berth.

Good luck with your design, do let us know what solution you fitted.

On a previous boat there was an ‘L’ shaped bracket shaped to fit the anchor locker rear bulkhead on the long arm of the ‘L’ and through bolted to it. The short arm fitted under the deck and had a hole drilled through it. A hefty Eye Bolt came through the deck and through the ‘L’ bracket. The removable inner forestry was clipped to this and tensioned with a large lever type thing.
On the spreader was a slotted holder for the fore stay when it wasn’t in use to stop it flopping around . The lever thing was tied off to a coach roof handrail.

Thanks for replies, all.

This stay will be permanently mounted ( I hope! ) with a furler carrying a 95% Solent-type jib. A 'slutter' sort of 'cutter' rig.

I have a hefty Wichard U-bolt which I hope to fit through the foredeck. The question is 'can I fit it far enough forward to utilise the SEMI-bulkhead which once stored the anchor chain?' That would be beefed-up with glass/epoxy, if so.

If not, I'll need to craft and mount a 'deckbeam' of sorts, muchly reinforced with carbon and this carried down onto the hull sides akin to 'knees', to spread the load down.

I'd rather avoid the angled chain/highfield lever or Dyneema strop dividing the berth(s), if I can.