Water-resistant lead screw nuts for wing profiles in racing sailing boats

Technical Specifications:

• What was needed:  A racing sailing boat that floats above the water surface by converting the water pressure
• Requirements:  100% freedom from lubrication and maintenance, no adverse effects from seawater, dynamic movements, resistance to the required loads, smooth running, low weight, simple assembly
• Products used:  dryspin® trapezoidal thread nut, igubal® rod ends, iglide® J plain bearing bush
• Success for the customer:  The igus® threaded nuts, plain bearings and rod ends installed by guarantee low coefficients of friction for the necessary sliding of the upper joint, dampen the vibrations transmitted by the rudder and, in comparison to the metal counterparts, do not require any lubricants and are easier to remove from the salt residues of the clean the sea.

Problem:

The students of the Polytechnic of Turin build racing sailboats with airfoils. The pressure exerted by the water on the profiles causes the boats to hover, reducing hull friction and allowing full use of the wind's propulsive power. One of the systems developed is the rudder mount. It allows sailors to adjust the angle of attack of the profile at the rudder end, instantly providing the desired lift for the racing conditions at hand.

The main challenges to be overcome in the design phase were:

• To avoid system degradation due to the marine environment and the dynamic conditions of movement
• Components that can ensure the correct conversion of rotary motion into linear motion
• A system of bearings and flanged bushings to support the linear movement of the pin to ensure low coefficients of friction at the interface to preserve contact surfaces
• The correct kinematic movement between the grub screw and the rudder stock through joints that accompany the desired angle of inclination and planing. Other critical design factors related to the team's goals include: limiting the weight and complexity of the components used, and the overall environmental sustainability of the system

Solution:

A dryspin® threaded nut was installed, which converts the rotary movement of the belt pulleys into a linear movement of the steel pin. The main characteristics required are: correct coupling with trapezoidal thread of a steel pin, resistance to the required loads, smooth running and no deterioration of the pin thread, which does not lose its properties in humid and saline environments. Flanged bushings are also used which, mounted on the fittings, support and allow the pin to slide in the smooth sections.

Main features:  Resistance to the slow but repeated sliding of a steel bar with radial and axial dynamic radial and axial loads and low coefficients of friction. Ball joints are installed as the third element, which allow the rudder stock to be inclined relative to the horizontal displacement of the threaded pin.

Main requirements:  Allow rotation, tilting and sliding of the vertical bar, fixed to the rudder, with low coefficients of motion.

All igus® parts used are resistant to damp and salty environments. No lubricants are required, they are lightweight and easy to assemble and maintain.

dryspin® lead screw nuts

igubal® rod ends

iglidur® Flange Bearings