Arne and Graeme,
first of all, thank you very much for sketching even more sail plans! I'll get to those further below.
I value both of your advice regarding the mast foot and tabernacle issue a lot. I also fully understand that it would be way easier to have a thru-deck tabernacle. Yet, giving up the V-berth really is not an option. I do like the ease of just getting up, set up the kettle and start the day. Re-arranging the saloon from sleeping mode to day mode is something I really want to omit (I am a lazy bum - sometimes). Also, from a social point of view, when living together in such a confined space it is very helpful to have two "separate" rooms from time to time. This may not apply to every relationship, but we learned during the one year long sailing trip on our former boat, that being able to seclude oneself for some hours or even some ten minutes is crucial for the well-being of our relationship. A separate salon and V-berth makes a huge difference here, even if only separated by a curtain. (also, I just finished some cozy, seagras-stuffed mattresses for the v-berth this spring. Don't want to give up on them)
Yet, I like the challenge of designing this above-deck tabernacle structure. Probably it will be ugly, heavy, adding a lot of windage ... people will laugh at me and point to the next thrash yard. Still, I want to test this idea of mine.
Attached are some crude sketches of the above-deck tabernacle (really need to practice hand-drawing...). Also, the actual deck layout and hull above water as foto reference. It can be seen that the hatch is located at the front end of the v-shaped deck step.
The tabernacle would stand on transversal beams. Those could be two diagonal full beams (a) or one transversal full beam with two diagonal half beams (b). There are points for each design:
version (a) definitely shows longer beams, thus requiring stiffer beams. Yet, they would allow diagonal tube in four almost opposing directions. For every wind direction, there would be beams with tension load and beams with compression loads.
Version (b) would allow one shorter beam length because it is transversal -> less stiffness required. Only two diagonal tubes for the rig moment would be required as a minimum. However, load distribution of the mast moment would not be as smooth: for all wind directions except dead running, one diagonal tube will be heavily loaded with compression load. Not favourable, tension loads are more forgiving than compression loads (buckling, etc.).
All these challenges would be manageable, its just a matter of sufficient dimensioning. I will have to decide which option would be the most simple and most failsafe. By now, I tend to a modified version (b): only one able transversal beam, no diagonal beams at all. And then only two able tubes leading diagonally backwards (just as the diagonal half beams I've sketched in (b)).
Material for the tabernacle could be stainless steel (expensive, shiny, heavy), galvanized steel (cheap, ugly, heavy) or heavily fibreglassed plywood (cheap, light)... By now I tend to galvanized steel or fibreglass.
The whole above-deck structure would be mounted by only four bolt connections to the hull. The connection points would be stiffened from inside as shown in the detail drawing. The inside stiffeners would not be too big in dimension. Their main function would be to better distribute the loads into the hull. Other than showed in the sketch, I would probably extend them more inwards at the deck area (to be more like a knee panel), thus reducing the distortion of deck and hull. Material for the stiffeners could be stainless steel or fibreglass... Probably the later one.
Paul