Inside the carlines, in which case the callings will need to be shaped or canted to conform to any tumblehome.
On top of the deck, fixed to a sill which is through bolted to the carline.
There are many variations on both methods.
The first method will make for a neater finish on the inside but will be more prone to leaks and the carlings will require shaping before fitting.
The second method should
make for a dryer interior
and be simpler to construct.
However, that box will ruin the look of even the most elegant hull.
A well shaped trunk will on the other hand enhance the appearance of any hull shape.
Much of the shaping is needed to counter the optical illusions created by building on a shapely hull and deck.
Cabin sides which are vertical built on a sloping deck will appear to slant outwards.
So the sides need to be built slanting inwards towards the top, just a few degrees is all that is needed to offset this optical illusion. Many boats however are built with a more pronounced tumblehome.
A flat horizontal cabin top will appear to be hogged, and look hump backed.
So a small amount of sheer curve is needed and the top will look much better if it slopes slightly up towards the stern.
And a curved top to the cabin will not only look good but drain water away much more quickly than a flat top.
The sides also need to curve in a horizontal plane to reflect the curve of the hull not only for looks but to allow for usable side decks.
Some of the most elegantly beautiful designs have only very subtitle amounts of sheer, tumblehome and curve.
It does make for extra work but the finished look will be very much worth the effort.
It is possible to make a â€˜boxâ€™ with simple butted corners but this wont be very strong, any exposed end grain will be prone to rot and it will look cheap.
The preferred method is with a nicely radiused, rabbeted corner post.
The best posts are made from a solid piece but this can be tricky as you will have to allow for any desired tumblehome.
It will be much easier to laminate them up from two separate pieces.
The lower end of the post will have to fit the carling and beam and be beveled to allow for the tumblehome.
The top will need shaping to conform to the slope of the top.Leave some extra material on the outer radius so that it can be fared to the sides after construction.
But again a certain amount of subtlety and compromise is required.
Too much camber while it will allow more standing headroom below will tend to look too much like a barrel.
And any force pushing down, such as foot traffic will have a tendency to force the cabin sides outwards. This is why church builders had to resort to the flying buttress.
So, a gentle curve well supported at the ends and with supporting beams in-between.
It is unlikely that you will have access to sufficient lumber with the grain running in the correct curve so, forget about sawn beams.
Well made laminated beams can be an extremely attractive overhead feature.
And a cabin-top laminated up from layers of ¼ inch marine grade plywood will have great multi-directional strength.
Mignonneâ€™s main-cabin had originally been covered with tongue and groove boarding which, had then been covers with canvas.
As the boards, once they were cleaned up looked rather attractive on the inside I retained them but covered the whole on top with painted plywood.
On the aft part which, I had to rebuild I again used tongue and groove as the first layer, for its decorative effect then laminated plywood on top.
An ugly, boxy, dog kennel stuck on top of an elegant hull will draw everyoneâ€™s eye including the owners.
I have seen too many that I would love to take a chain saw to.
A well designed cabin will enhance the beauty of any wooden boat and enhance the ownerâ€™s pride.