On Goblet Hulls

This brief paper was inspired by the author's coming across some intriguing-looking hull cross-sections (see figure 4 "a & b" and "c") of a type of 19th century Northern-European sailing vessel, the "Ewer", a type of boat typically 15 to 25 meters long and with two masts and often used to transport goods in shallow waters with considerable tidal ranges or for deep sea fishing. For lack of a generally accepted term they are called "goblet hull" here.

Pondering why this unusal and - when constructed out of wood - difficult to manufacture cross-section had been chosen, the paper argues that the following design features were  desired : (1) A reasonable wide flat bottom to maintain an upright position in the case of ground contact at low tides. (2) Sufficient width of the hull at the water line for sufficient transverse stability. (3) A significant volume for solid ballast as far below the waterline as possible, again to contri-bute in transverse stability.

It is noted that far from all "Ewer" type vessels featured a goblet hull yet that numerous did.

Contemplating the goblet hull on Ewer type vessels, the author was reminded of one aspect of the almost a millenium older "Knarr" type vessels - a type of roughly the same overall dimensions as the "Ewer". At least some of them featured, in the midship region, a cross section somewhat reminiscent of the   goblet hull of the  "Ewer" type (see figures 2 and 3).  

The "Knarr"type had already been the subject of a previous paper from the same author, "On the First Northern European Sailing and Cargo Vessels ", yet this current paper touches in particular on that ships peculiar cross section geometry, called the "ballast bilge". It is argued that this cross-section was adopted - despite it being extremely difficult to build at that time - in order to provide a greater volume for solid ballast as low in the hull as possible. The earlier paper had already demonstrated, that the "Knarr" type did, under certain loading conditions, need to carry ballast.

This insight, then, creates an arc that connects two types of roughly equally large sailing vessels, over almost a thousand years : One, the "Knarr" stood at the very beginning and the other, the "Ewer" at the very end of the era of wind-powered ships.