By JB Braun, North Sails Design Services, 2016

Phase 2A Completed November 2016  | Phase 2C Completed January 2017 | Partners: North Sails, Wolfson Unit

The Downwind Aero Moments & Forces Phase Two builds upon the successfully completed Downwind Aero Moments & Forces Phase One, which used fluid-structure interaction modeling to simulate the downwind flying shapes for three yachts that represent the modern racing yacht spectrum. Using North Sails's 3D Finite Element Analysis (FEA) tool "MemBrain," Phase Two measured the aerodynamic forces of yachts sailing at tighter apparent wind angles (AWA) than were measured in Phase One, thereby providing a more complete look at off the wind sailing setups. Phase Two also captured the effects of modifying the girths of mainsails and downwind sails by simulating yachts across a rnage of sail plans across a range of AWAs and true wind speeds (TWS). Additionally, as Phase One could not accurately simulate the flying shapes of sails at deep AWAs due to unsteady flow and oscillations, Phase Two will develop the technology necessary to overcome this challenge.  

Sailing World - September 2017


Learn how to apply SYRF's research on-the-water with JB Braun's Sailing World article on the science behind the spinnaker curl. 

The primary advice for spinnaker trimmers today is the same as it was 50 years ago: "Ease the sheet until the leading edge begins to curl, then trim in slightly. And repeat." As a sail designer immersed in the science of how to make and trim fast sails for most of my life, I find the technique more than a little disappointing. Doesn't modern technology have a little more to offer when it comes to the art of making a boat sail fast downwind?

Yes it does...


Completed November 2016

Phase One simulated downwind sails at AWA typical of windward-leeward racing. However, with the popularity of coastal and distance racing on the rise, yachts are spending more time reaching at higher AWA. Therefore, it is important to also provide handicappers with the forces and moments of downwind-reaching hybrid sails, such as Code Zero type sails, typically used by asymmetrical yachts. To this end, Phase 2A will capture the moments and forces for two types of Code Zero sails across a range of AWA and TWS for the same Swan 42 ad TP52 designs used in Phase One.


Completed November 2016

Handicapping yachts involves understanding differences in performances between sail plans and configurations and having the ability to quantify the effect of a change in sail area or design. By independently varying the girth of the mainsail and spinnaker, Phase 2B captures the aerodynamic differences between five sail plans across a range of AWA and TWS for the Swan 42 and McCurdy & Rhodes 48 Carina. 

Completed January 2017

The current tools available to sail designers and handicappers to simulate downwind flying shapes break down at wide AWAs; this became apparent in the deep AWA runs for Carina in Phase One as the spinnaker oscillated between port and starboard. Therefore, Phase 2 aims to develop the computer simulation technology necessary to average the forces and moments of a sail across an entire oscillatory period. Developing this capability is paramount to accurately predict the performance of yachts whose optimal angles are deep AWAs.



Phase 1 & 2A TP52:

Phase 1 & 2A Swan42:

Phase 2B Swan 42:

Phase 2B Carina:

Phase 2C Carina:


If you use any of the data provided on this page, please use the following information for your citation.

Author: Braun, JB

Title: SYRF Downwind Aero Moments and Forces Phases 2A & B

Date: 2016

Publisher: Sailing Yacht Research Foundation

Electronic Retrieval Location:

Downwind Aero Moments and Forces by Sailing Yacht Research Foundation is licensed under a Creative Commons Attribution 4.0 International License.

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