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WHERE THE SMALLEST DETAILS MAKE THE BIGGEST DIFFERENCE

Following a year-long design process SailGP Technologies is poised to update the fleet of F50s with revolutionary T-foils that will provide greater acceleration and speed.

The F50 has stood the test of time. Ten boats, strictly identical, racing at speeds of up to 50 knots (92kph or 57mph) have faced each other on the international SailGP circuit since early 2019.

But behind the scenes is a focus on constant improvement and a design team that identifies opportunities to achieve the performance trifecta of speed, strength and stability.

The T-foil, the result of a year of design work across a multi-disciplinary team, will soon replace the L-foil configuration that has carried the boats through more than three years of high level training and racing.

The design team at SailGP Technologies was asked to overcome the limitations of the older style foils.

A key challenge was to overcome the relatively low cavitation inception speed of the L-foils. Cavitation is a phenomenon where vapour bubbles form within a liquid at low pressure regions where it has been accelerated to high velocities. It presents as an issue when F50 boats try to take off and to foil at high speeds.

“The L-foils are very long structures that bear up to five tonnes - this is the full weight of the F50 boat and the force to counterbalance the side force generate by the jib and the wing ” explains Ignacio (Nacho) Castaneda Sabadell, head of design at SailGP Technologies .

“Being such a long structure, the minimum thickness is dictated by load. You want your elbow, which is always in the water, to be as thin as possible to deliver a higher cavitation inception speed while being able to handle the load generated on the tip which is equal to the weight of the boat.”

“When cavitation appears, you have an increase in drag, which means you need more driving force from the wing to keep accelerating, but you also lose the ability to generate enough lift so the boat can fall off the foils and crash.”

T foils offer an opportunity to delay the appearance of cavitation and thus allow a higher boat speed.

Modeling shows they will increase the maximum speed of the F50 from 53 knots to 55 knots while reducing the amount of righting moment we need to generate with the rudder differential.

“Righting moment is related to the center of effort of the foil,” says Nacho. “With the T it is outwards, but with the L it is inwards. Currently we use rudder differential, which means we have one rudder pulling up, and one down. But with the new foil design we will need to generate less righting moment from the rudders reducing rudder drag.”

Another benefit is that T-foils are are significantly thinner than their L-shaped counterparts: while L-foils are roughly 12-14% thickness to chord ratio in the elbow and reduce to 10% in the tip, the submerged part of the T-foils shaft is 8.5-11.5% thickness to chord ratio and the foil wing 9%. The L-foils are fully composite, the T-foils utilize three materials including composite and steel in the shaft, and titanium in the wing.

T-foils have been the subject of more than a year of intensive work by SailGP Technology’s structural engineers working on the composite components, mechanical engineers on the metal components, hydrodynamic specialists, hydraulics engineers, and computer simulations.

SailGP’s F50 fleet will be fitted with the new T foils later in 2022.