Annie, thank you for the efforts on the blog - they make great/interesting reading (no surprise really given your previous record as an author of fascinating books!)

The tabernacle discussion is interesting too. We went for a forward opening tabernacle, but given the layout of things the mast actually steps about a metre below cabin height, with the pivot about 300mm above the roof line (swinging thru a slot in the cabin roof). 

The original design from the designer called for building a wooden case dividing the cabin in two with the mast stepped onto the keel and pivoted at cabin roof height (wherry-style) - but this "mast version of a centreboard case" so wrecked the usability of the cabin we started again, and constructed the tabernacle and step in steel (yes, very infra-dig I know). So, the structure is now a piece of box section secured to the "keel", with the open sided box for the lower part of the tabernacle welded to the top, and four steel box-section braces securing this between the deck clamps, port and starboard and a substantial laminated beam forward. This is then bolted (thru the cabin roof line) to the upper part of the box (with the (yet to be finalised) pivot.) The obvious problem with this design is the opportunity for leakage! I think the best current plan is to make a large fabric "boot" that is seized to the mast above the pivot and secured around the edges of the opening in the cabin roof. A bit like a gearstick boot in a car. Time will tell if this works.

We are using an alloy-lamp-post mast and planning for only 16-18sqM of sail so hopefully this will be strong enough!

As a picture is quicker than all these words, these two pages in Befur's Blog might help add some clarity... one  two and following pages.

Annie, I still think you are going to beat us into the water with a "fully finished" boat, our current plans are to install the steam plant and try to "see if it floats" before the winter, and then aim to fit the sailing rig in the following season :-/

David Tyler wrote:You're both right, of course. The load when sailing is taken by the bottom of what I think of as the fender locker, but I understand is now the woodshed (Tys tie's fender lockers totally fill with water when hard on the wind in fresh conditions, and I was under the impression that wet wood doesn't burn as well as dry wood...) I was thinking of the times when I was short tacking with both boards down, and when the windward board was inadvertantly dropped. There was definitely some discernible movement, though of course Tystie has pivoted boards, which transmit forces through the pin, and Siblim doesn't.

Your port side shelves will be fine.  Put something similar on the other side, and all will be well.

I shouldn't have thought that even with both boards down, the windward one would put any serious loading on the inside of the box, but I shall certainly assume that you are correct.  I have an enormous capacity to worry and am now thoroughly discomforted with respect to the bilgeboards, so I am fitting an extra 12mm, shelf, at the same height as the stringer the deck lockers are attached to.  (From what I can gather from drawings showing the bilgeboard down, this is where the top will be.)  Well filletted to the bulkheads and board casing, I trust this will do the job, although the shelf below it will be somewhat less useful.  On the starboard side, as I said, I am fitting a fore-and aft counter, which is about 800 mm long and, fortuitously, at exactly the correct height.  With the bulkhead cut, coated and framed up, it would have been more than vexatious to have to start again on that side.  I can't put a similar set of shelves that side, because the passageway is already well to starboard of the centre line.  The amount of strutting and bulkheading in the heads compartment will put HMS Erebus to shame, when completed!

ueli lüthi wrote: as the leeward board will take the big part of the forces. it's the outward side of the case that needs to be strong on bilgeboard top level – and there the hull should provide sufficient strength…

utnik

David Tyler wrote:

…Remember that the inner side of the bilgeboard case needs plenty of support at the level where the top of the board is going to rest against it.

utnik

David Tyler wrote:

Graeme and Ron,

I tried, and failed, to persuade Annie set the tabernacle in the boat with the open side aft, and then to put the pin through the heel plug, where it can do no harm. Easy to do, and a no brainer where there is no coachroof to clear, as is the case with SibLim. And as you say, for occasional use there need be no pin. This arrangement has been used for centuries in the Yorkshire and Northumberland cobles, and would work well here, too.

But as Graeme says, should I (or the rest of you) change my mind, I can always reverse the tabernacle!  It's not installed yet.