Hi there, I am Nol.
I red your discussion about Wantoo.
In the years since this first Wantoo for the Design Challenge I made lot's of proa drawings: larger, smaller, with cabin, without cabin….. Even a monohull lately.
Meanwhile each year we made about 30 sailing days with handicapped people on the Blind Date.
There are so many things to develop and to test on Atlantic Proas!
A folding system is just one of them. And a fence construction is just one of the ways to materialize it. The 'harmonica system' of the first Wantoo is hard to beat. I agree that a straight or slightly bent beam looks better (and 'faster').
The rudders are another detail that needs to be developed. We are working on hydraulic control for the Blind Date rudders now.
I see that as a first step in the direction of foiling rudders.
The HarryProa concept is more suitable for foiling than any other sailing boat concept.
In mu opinion foiling is the future. Not 100% foiling, like we have seen in the America's cup. That is only feasible for extremely light and vulnerable boats: 'the foiling few'.
A foil can make any reasonably light and slim hull faster and more comfortable, even when that hull is partly in the water.
There is a lot of engineering work to be done in finding smart hull-foil combinations, that work well in al sorts of circumstances: up wind, down wind, strong wind, light wind, high waves, low waves….
So let's not waist too much time discussing details. Money is the key. We need people who are willing to invest in prototypes!
I am talking about systematic research to find the perfect leeward hull - foil (=rudder) combinations for Atlantic proa's from small (5 meter) to large (20 meter).
Nol
On Monday, December 8, 2014 12:39 AM, "cruisingfoiler@yahoo.com.au [harryproa]" <harryproa@yahoogroups.com.au> wrote:
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.
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:
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
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Posted by: Nol Twigt <noltwigt@yahoo.com>
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