A question of balance

A question of balance

Friday August 16 2013 Author: Caterham Composites Location: Germany

Overview

Caterham Composites is a specialist company delivering turn-key lightweight structural solutions to all industries. We offer fresh thinking, new perspectives and an unquenchable thirst for improvement. As part of the Caterham Group we have the technical resources available to offer to the wider world; CFD technology, crash and NDT capacity will enhance your project. Thus, we are now ready to offer our expertise and technology to the marine industry.

 

 

 

Daggerboards

There are many similarities to F1 design in the high performance marine industry. One example is daggerboards. They are the equivalent of wings, providing traction but at the cost of increased drag - therefore an optimum balance needs to be found. In the case of F1 this varies for each track. For yachts it depends of cours on the type of yacht and the hull shape but also on environmental conditions such as wind speed or sea state.

Asymmetric daggerboards are used in the majority of high-performance racing yachts such as open 60, Volvo 70 and the new VOR 65. Their development was pioneered by the multihull classes. The ORMA 60 class had success with curved daggerboards to provide lift as well as lateral resistance, and most recently America’s Cup teams have invested heavily into developing daggerboards.

 

 

*Pressure distribution on both sides

*Pressure contour showing map showing the inboard and outboard sides of the daggerboard

C-class Catamarans

There are very few design restrictions in this class, so boat development has continued at pace and is generally at the forefront of yacht design. Becasue of this they have become known as the little Americas Cup. Wingsails and lifting daggerboards were all seen on C-class catamarans long ago.  Hydrofoil C-Class catamarans have also been attempted but, to date, the benefits have not been realised as a result of reduced righting moment and a higher induced drag.

 

We are proud to work with Team Invictus to analyse and develop their daggerboard geometry and construction. We are doubly proud, as this work recently formed the basis of a Bachelor thesis for one of our trainee engineers who specialises in fluid dynamics.  

The Process

First, we modelled the yacht and created a virtual environment to generate realistic scenarios. Catamarans generate a maximum righting moment when the windward hull is just clear of the water. However they will spend most of the time with the hull flying higher than this as, when you touch the water with the windward hull, drag is doubled and you go much slower. We therefore set the heel angle at 10 degrees. The speed and leeway of the yacht were varied to get the full range of boat speeds and angles this provided us with the various pressure fields using CFD, the worst being high speed and high angle of attack. Then we are able to couple our  CFD and FEA capabilities to understand the fluid structure interaction. i.e how does the daggerboard react at varying speeds and angles of attack? By understanding this relationship and the consequences of each decision we were able to find the optimum balance between weight, lift and drag.

 

* Deformation of the daggerboard at peak load using fluid structure interaction capability.

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