Scantling of sailing yacht mast and sail deformation simulation using Finite Elements

Abstract

When developing a sailing boat, the design and scantling of the rigging system supporting the sails is often a critical part of the project. Those rigging systems (mast and standing rigging) are composed of cables and beams subjected to high compression loads and large deformations. One of the most difficult tasks for a rig designer is to estimate the maximum loading condition for a rig. These loads determine the mast tube dimensions such as wall thickness and the stay diameters. As a consequence, the loads basically determine the total weight of a rig. The constant drive for better sailing performance pushes the design to the limits, even for cruising yachts. Standard approaches to define loads for a rig start with the righting moment of a yacht of heel. In rig dimensioning procedures it is a common practice to take the righting moment of the sailing yacht at 30 degrees as a base to compute the compression forces in the mast tube and the tension forces in the standing rigging. With FEA performed on yacht rigs it is possible to determine the efforts in all parts of the rig and to predict deformations of the mast and the standing rigging.

A load model based on sail areas for application in FEA is developed. The tool consists of a force prediction model, estimating the external forces acting on the rig during sailing. Subsequently these forces are used in a finite element analyses to determine the structural behavior of the rig. In several analyses steps the rig can be optimized. Due to the generic set up of the tool, different rig configurations can easily be compared.

But defining loads on the rig for FEA is still a big problem. Without the right loads even the best simulation of the rig structure is worthless. There are many different loads on a sailing rig. Pretension, also referred to as “dock tuning”, is one load case. Sail loads as a function of wind velocity, apparent wind angle and sail combinations are a second case. A third case is inertial forces when the yacht is moving with all six degrees of freedom and big accelerations in waves (e.g. a rapid deceleration when nose diving). A fourth case is the weight of the rig itself which has to be considered with large rigs.

Finally, conclusions and recommendations are presented, as well as suggestions about future work related to the project.