How Owls and The Tear Drop Design Are Connected.

On the bbc the other night a nature program on how owls fly without their flapping making a noise and alerting their prey.
The presenter highlighted the special features of their wing and compared them to a pigeon and a hawk. In the case of the owl it showed how feather 'tufting' absorbed sound and emphasised the fact that unlike the others it was a slow flying bird.
I think the pigeon was ill - placed in that group as it is not a hunting bird but more a seed herbivore. It needs speed however to escape predation and so perhaps its inclusion was permissible.
The differences in body shape were noted but the elephant in the room was that they did not stress how important that was in addition to the wing features.
What was so fabulous to see was the owl in flight, slowish, steady, infrequent flapping and mostly in descent and levelling off. What stood out was the shape of the owl in flight. Every feather adorning its marvellous face and neck standing vertical to present the blunt and non-streamlined presence that its face is and then this tapering very quickly to its sharp tail to present a true tear-drop form.
I contend that it is this as much or more than the wing form that enables it to course through the air silently and without ruffling the air it is in. This is easy to comprehend just visually. The broad wing spread of the owl announces it is designed for slow flight.

Help required defining the geometry of Tuanella 3 - ? complex integrated conincal?

Tuanella 3 was made from a single sheet of aluminium. The remit was to have a hull like structure blunt (rounded) at one end and sharp at the other - subserving those fundamentals I hope to elucidate about the generality of most natural forms that find their way through a gas or fluid.
A thin sheet can be formed into a conical structure by bringing the ends of one side towards each other and the angle formed can be changed by overlapping those ends.
If the apex of the cone is closed and the overlap sealed then a container is generated. The standard laboratory funnel filter is made by indenting a disc of filter paper from a point on its circumference towards its centre and allowing the indent to overlap and lie flat on the cone so generated.
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If an oblong sheet is cut anywhere along its length from its margins towards its centre anywhere a cone can be made. Choosing to do this in three places one can create a container which will float if the cut edges are sealed.
Unlike boats made from single sheets of metal where the sheet is sectioned and joined edge to edge
and generated angle at those joins the use of multiple cones results only flat and curved surfaces which in terms of boats makes for an aesthetic appearance.
Selectively cutting can produce many shapes with a range of cross-sectional profiles that approach
those seen in many boats with the sole of those shape varying from a rounded v to a flattish section that might be seen to offer a degree of bilge to the form.

The general overall cross section is V and this offers a bilge that will plunge significantly before offering buoyancy. However if the hull is rotated laterally in the static situation that I propose for the catamaran then this plunge effect is diminished markedly and replaced with increased buoyancy and a tendency to plane. In the dynamic situation of a single hull driven by wind heeling will also rapidly reproduce this situation . Heeling will, of course reduce the directional stability the V section might offer but can't at least be countered somewhat if there are a pair of angled rudders. which is particularly good for the catamaran concept.

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Some observations on the need for strength in hulls of catamarans.

I understand that one of the principle reasons the costs of catamarans is high related to the obvious ie there are two hulls. In the nature of any hull has to be the inherent strength by way of its shape to hold it shape and secondly retain attachments or resist separation of attachments like the keel, rudder, mast, engine, bulkheads. Not only do catamaran have over mono-hulls the spread of the load but especially when it comes to keels they mostly do without them stability being the mutual out-rigging of the other. If the underwater surface offers some directional form this too is a bonus .
I contend the reversed tear-drop form made in the single sheet manner I have described does this well as a mono hull but for the  hulls of catamarans there can be another notable bonus. If the hull topsides are rotated inwards so as to make the outer sides nigh on vertical the increase in the free-board offered remarkable and with this rotation outwards of the bottom of the hull so too and significant increase in the boats stability. Of course the free-board of the inner sides is correspondingly reduced. This gunwales of these side now form the margins of the connecting pan like floor that will join them.
The deck is made from the 'roofing' that connects the outer gunwales.
The space  that has been generated from doing this is quite staggering and all still without any intrusion of structures above the deck -  pure central living space.
Geometrically the cross-section along its length is an isosceles trapezium (trapezoid in USA). Therein  are inherent triangular derivatives that offer great strength here especially from the distance in height from the floor to the ceiling (deck).
In terms of offering a site for suspending a keel, fixed or lifting, placing the engine, chain lockers and workspace it is perfect aft wise and forward great for a mutual below deck dining and galley with immediate access to the hull containing the cabins, showers and heads. or otherwise it is perfect.
An above deck cabin and wheel house is easy to install between bulkhead and thus without structurally affecting the hull.
The internal rotation of the hulls means the forward 'flatness' of the sole become some v shaped offering more directional stability.

In the diagram I have treated each pair of hull identically by adding the two deck options and the two floor options . In each pair I have shown the inner side of the hull cut down to bring the floor down .
Even if this is not done in the lower pair the shaded area represents the gain over the upper pair and this is a feather off one and half times the cross section of one hull and this is without the curvature of the deck added in. Indeed a great increase in space and hopefully the movement of buoyancy outermost.