From Screen to Sea

On the Modeling and Construction of a 75 sqm Yacht Hull

by Reinhard Siegel

Introduction

Juliane Hempel of Yachtkonstruktion Dipl. Ing. Juliane Hempel was given in 2015 the commision for the design work of a 75 square metre skerry cruiser. The yacht is based on a never built Gustav A. Estlander design of 1927. MultiSurf was used extensively for the 3D modeling of hull, deck, structural parts and the layout of the hull planking. The yacht is currently under construction at Yacht- und Bootswerft Josef Martin, Lake of Constance.

75 sqm yacht (design by Juliane Hempel) – bow view

Rules for square metre yachts

The square metre yachts (skerry cruisers) are regulated by a set of class rules. Basis for the hull regulations is a table of hull particulars of an ideal square metre yacht. If certain measurements exceed the ideal ones, displacement, mean breadth, freeboard and length of keel are to be increased.

Table I: ideal hull particulars (taken from “Rules for skerry cruisers (square metre yachts”, SSKF, 2013)

Measurements are taken at a variety of horizontal and transverse sections.

Definition of horizontal and transverse measurement sections (taken from “Rules for skerry cruisers (square metre yachts”, SSKF, 2013)

Model construction

Mastercurves of the C-spline Lofted Surface hull_0 and the B-spline Lofted Surface keel_0

The hull is split in two parts – the canoe body and the keel appendage. The canoe body is a C-spline Lofted Surface on B-spline mastercurves. Attached to it is the keel as a B-spline Lofted Surface, using a snake and a Procedural Curve for tangential joint and several B-spline Curves.

For direct comparison of hull dimensions against rule measurements the class regulations are implemented in the model by variables and formuals.