Boom Flex Analysis

By July 31, 2013 All News, Marine News

Sailing is a sport with many variables. This means that there is always something to improve on to make your boat point higher, go faster, or both. Since it is not possible to control them all, we strive to research and discover where the next improvement should be made in order to achieve the greatest gain.

The Moth class has come along way in recent years. Now that the boats are up and foiling, a speed differential as drammatic as was gained by the hydrofoil is no longer on the horizon. As a result, smaller improvements over many areas are the name of the game.

Fast-forward to today and through our constant analysis of the class, we have found that the next big speed gain will come from taming and controlling the aerodynamics of the sail. And from that, boom stiffness is the next critical step. Australian Olympic Coach Emmett Lazich says the following on the topic:

“Stiff booms are important in most classes, and they are critical for the Moth class. With mid boom sheeting and a narrow angle for the vang direction of pull, the Moth boom gets a serious work out.

“There is no debate that boom flex hurts performance. When the boom flex’s in any direction in a gust, the unsupported mainsail foot deepens just when we’d prefer it to flatten. But the problem with boom flex is far worse than just controlling the foot depth. In a gust we want automatic flattening and twisting of the mainsail (progressive fanning) from the head down, and mast bend is a primary tool for achieving this. There is always a time lag before the mast will bend in response to a gust. The mainsail air pressure changes increase loads on the mast and boom, and if the boom bends to easily, that means the mast will bend later. Delayed mast response will require excess trimming, steering and control line adjustments, and since there is no such thing as a steady wind for a Moth, top speed will be less.”

Emmett’s words become critical when the conditions are marginal for foiling. The speed differential between being up on the foils or wallowing in the water are crystal clear. When in low wind-speed, often a small body pump is needed to encourage the boat to foil. That pump is when the leech and foot need to remain bar taut, and any boom flex reduces the efficiency of this pump by huge amounts. This moment is that all too critical point to overcome in order to launch your boat onto the foils.

Following Emmett’s intuition, we conducted our own empirical research on the various types of booms currently in use in the Moth fleet. We found that our newest booms are by far the stiffest in both horizontal and vertical planes, as can be seen below.

Vertical Deflection

Vertical Deflection

Sideways Deflection

Sideways Deflection

At CST Composites we are constantly researching and developing in order to continue being market leaders in bringing the fastest technology and gear to you at the best price. Stay tuned for more exciting developments to our product range.

Testing booms on our high-tech Instron machine

Testing booms on our high-tech Instron machine

Andrew Cuddihy, 18′ Skiff Legend has one of our new booms and these are his thoughts here.