How high to make the Bimini?
I would try not to raise the boom more than you have to. I would suggest trying 300mm (12inches) as a starting point. See how much headroom that would give. I am 5′ 10″ and can just stand up under the bimini when at the back of the cockpit, but at the front of the cockpit the engine box protrudes reducing that. If you try to allow for 6′ 2″ standing headroom you are going to be losing lots of mainsail area. We spend more time sitting in the cockpit rather than standing – so the critical thing is to have good sitting headroom even if you have to stoop to move about the cockpit.
Of course you also have to think about how the framework fits, and whether it can fold up/down, and how many separate frame sections are involved?
Whatever you do will be a compromise.
Toilets and holding tanks
There are only 2 or 3 Atalanta’s where the toilet has been moved to the aft cabin – so you won’t get much in the way of feedback to this. Those few who have them in the rear cabin (at the front near the hatchway and to one side) speak positively about it.
I am not really a fan of the idea. Perhaps because the headroom in our rear cabin is very limited so I cant see how it would work on a Titania.