Davis Wing

The use of the Davis wing shape and its subsequent limitations may turn out to be similarly applied to the tear drop shape boat in that the pressure head generated by the nose section as speeds increase cannot potentiate its energy on the tail section.

Detail of gudgeons on the hull

Two of four gudgeons demonstrating the excellent purchase on the hull, an area of detail where strength is important

Tear Drop Concept

In previous postings I have used tear drop freely and perhaps carelessly considering that there is a good deal of contention or confusion about tear drops and rain drops as contenders for the ideal streamlined shape consider the following link.The deformation of the rain drop in its gravity driven excursion rather puts it out of the running – it would seem reasonable that it is indeed ideal for the rain drop, one fluid volume finding its way through another. Tear drop seems to be the accepted shape of a tear or drop just before its downward departure (from the face) – essentially elongate, round nosed but quickly tapering to its tail.

Patently a whole family of different tear drop shapes can be, probably has been, generated using a range of liquids with different viscosities, surface tensions and densities. From such pictorial data an integrating algorithm might give some idea what tear drop shape is best with increasing 'rigidity' in the media'. ( we don't want our form to collapse).

What I have done is just a copy of what I see as the general foot- print and lateral lines of fish, birds, and water travelling mammals. From a biological view to a down to earth practical demonstration of it we can look at the following.
Albacore was the first sub in the world to be built with the now familiar "tear drop" -shaped hull. Previous sub types had flat decks and pointed prows to maximize speed and maneuverability on the surface. In contrast, the Albacore was a cylinder with a rounded nose and a tapering tail that allowed it to move more easily while submerged. The new hull shape increased the speed of the ship under the surface dramatically. It was so quick and so maneuverable that when submerged that sailors dubbed its movements "hydrobatics."

This shows the stern as a gusset riveted after the initial folding. It also shows the gudgeons on the on the stern which match gudgeons on the rudder. A long pintel connects them all and allows for easy lifting and removal of the rudder.

Harking to my first post and my enthusiasm for the reverse tear drop shape one needs to envisage in general terms what is actually happening as that shape travels through the water.
If the viscosity of the media was considerable and elastic there would be an initial material build up across the rounded nose as penetration occurrs. The maximum diamater having broached the continuum, now finds its energy in a collar of the broached media potentiating, enabling or squigging that section behind the maximum diameter ( tale of the tear drop) forwards.
As we are in water and this being incompressable, the forward movement of that shape has to result in a displacement. and this is in the direction of least resistance, which for boats will be a collar of water on the surface. It has been found that the shape and depth of this collar is so dispersed around the bow's maximum diameter to act as in recoil and not creating an energy wasteful wake.

Boat shape from the bow

The material for the boat is one of a 2mm 5000 series magnesium aluminiums which behaves very much like a spring plate with good recoil from modest bends and deformation. In making very small models this quality is duplicated very successfully using old X ray film.

In and under view of bow of boat

Aluminium sheet folding declaring definitive shape

Here one can see the curves in the bow of my design. The shape of the whole boat is determined  by twisting a single flat sheet to enclose a volume, much in the same way as the cut edges of a radius on a disk of paper can  be allowed to slid over themselves to form a cone.

The maximum curvature at any one point is singular. A right angle to the line of maximum curvature at any point is flat. And from this fundamental property of twisted planes issues the concept of  losing a volume enhancing curvature, present in almost all boat design. The exceptions being where multiples of twisted or bent planes are joined, as in sheet plywood and sheet aluminium boats.

I am suggesting losing this volume containing curve (bilge)  is offset by reducing the frictional surface over the whole wetted surface of the boat.

Under view of boat in progress

This picture shows a view with the bow in the foreground and the tapered stern in the background. The oak woodwork in the foreground is a construct to accommodate a cabin. The brackets seen along the gunwhale are of welded aluminuin to support the decking.