I’m impressed by the innovative folding concept in Wantoo. The deck styling is intriguing – more suggestive of a protected waterways cruiser than a true blue water craft, but these are my impressions.
On the engineering score however, there is much too observe. With few empirical precedents (Pen Duick IV’s beams are triangulated space frames) and in the absence of an engineering analysis (a presumption in the absence of evidence otherwise), I have a range of observations.
http://www.histoire-genealogie.com/IMG/jpg/002-pen-duick_iv-11-05-1968-2.jpg
While the cross beams are fairly stiff in the heeling plane the possibility of buckling remains due to the absence of a sheer web / diagonal bracing – despite the main crossbeam members being principally in tension and compression (rather than flexion). Twisting resistance to the asynchronous pitching moments of the hulls must be assessed. Of course the spacing of the 2 beams resists twisting, as does the trapezoidal beam configuration compared to a rectangular one, whilst noting that reducing the beam spacing on the windward hull increases the pitching torque applied to the beams by that hull.
Engineers can get it wrong too. You don’t need to go further than bridge failures:
Tacoma Narrows Bridge Collapse "Gallopin' Gertie"
I raised the Millennium bridge because it’s
rather unique in that it is almost a two dimensional structure – as are Wantoo’s
crossbeams. The bridge suffered from ‘synchronous
lateral excitation’ search for this term if you’re interested – or check out Wikipedia.
Having the beams pivot on the masts has a compelling logic: reduce the number of bearing points and the structure required to support them. Although this may not be an issue on Nol’s craft, if I were building a folding schooner rather than a cat rigged proa, I would change this feature. Whilst retaining the folding plan schematic, I’d construct composite monocoque beams and pivot at deck level just to weather of the leeward hull. The mast beam torque loading upon the leeward hull still need not occur, as the mast and cross beam forces can be isolated to common bulkheads. This would lower the centre of gravity and enable the centre of effort to be lowered (at least on a larger boat). I won’t raise the stakes any further than this as I’d have to start considering the relative merits of more or less freeboard and the mast bury required for rigs of differing heights.
Rig height (or rather absence of) on Cat2Fold and Wantoo ameliorate the points that I have made (in this and an earlier post), but thereby don’t test these concepts in an exacting way. I’m aware that Nol’s discussion suggests that speed is less important than reliably getting home. It seems to me that engineering of novel methods is also important when it comes to reliability, and it may well be that Nol has done or plans to do an engineering analysis.
As a conceptual design, it inspires much discussion and creative thought which is a good thing.
David
Posted by: cruisingfoiler@yahoo.com.au
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