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Maximizing Speed in Planing Boats
by Blackice
Quantum Sails' Doug Stewart hits the water on a regular basis to get real-life knowledge and feedback. Here are his interesting observations for planing boats.

J/70 Dazzler makes gains downwind during the J/70 Winter Series.

While engineering championship-winning sails starts with sitting at a computer playing with state-of-the-art software, it also involves hours on the water watching, observing, and testing. Already this year, I’ve been to Davis Island for the J/70 Winter Series and at Quantum Key West Race Week to look at J/70s and C&C 30s to get real-life knowledge and feedback, and I made some interesting observations. While my intent was to look at sail shapes and set-ups, something else caught my attention, and it may have a bigger impact in terms of speed around the race course!
Moving Weight

Many J/70 sailors – and possibly anybody with an attraction to small, planing boats – spent their early days in dinghies. For me, it was Lasers. I remember how much my weight moved fore-and-aft and side-to-side depending on sea state and wind velocity. In light air, I sat on the board with my legs to leeward, sheet between my legs, heeling the boat so maybe only a third of it was actually in the water. In heavy air, I was butt-back, hiking as hard as I could, moving weight as-needed to get the boat over the top of a wave. Once I was on the wave, it was back again, hoping the bow did not dig.

In the J/70 class at both Davis Island and Key West, we saw wind speeds from 6-25 knots, with moderate chop up to bigger waves. The polished teams at the front of the fleet moved their weight like I used to on a Laser. I am not talking about ooching or sudden weight movements – these were slow, controlled movements depending on heel angle or fore and aft trim. No doubt they had practiced and discussed their movements, as everybody on the boat worked the boat.
Big Gains Downwind

In these conditions, where the boats would come on and off a plane, there was too much weight aft for extended periods. This is also where I saw the biggest gains and the biggest losses occur. While the goal is to keep the rudder in the water, do not get stuck stern-down, bow-up waiting for the next puff. It’s a delicate dance in medium-to-heavy air as you certainly don’t want to end up bow-down and stern-up (or the next conversation will be how far to ease the asymmetrical halyard!).

Remember that the big gains are made downwind, especially in asymmetrical boats sailing at different angles. Going around the top mark is no time to relax.

In downwind mode in light air, the focus must be on heel angle, reducing wetted surface the best you can. Try to keep a consistent heel angle along with a fore and aft placement that gets the stern out of the water. To do this, practice getting the same people in the same places. In heavy air, the focus should be keeping the boat on a plane, so sail flat with an eye towards fore and aft trim.

In non-planing conditions, where you can go wing-on-wing, the focus should be reducing wetted surface, but with a twist – let gravity help fill the sail. Work on heeling the boat to weather (same side as the asymmetrical) and keep the heel consistent so the sail doesn’t bounce around.
Always be Racing

While the tendency is to breathe once around the top mark, you want to work harder on your downwind legs. Move the weight as needed and work together as a team. The payoff will be a lot greater than any gains that could be made upwind!

Understanding Mainsail Twist
by Blackice
Mainsail twist can have a large impact on speed and performance. Quantum Sails explains what mainsail twist is and how to use it to get ahead on the racecourse.

Technically, twist is the change in the angle of attack from the bottom of the sail to the top. Twist is necessitated by the wind speed changes, hence changing angle relative to the boat as you move away from the water. The drag induced by the water slows wind near the surface and shifts it relatively further forward, as opposed to the faster-flowing wind further aloft. This effect is exaggerated at lower wind speeds.
Understanding Twist

In the real world, twist means the leech of a sail must open up to some degree as we move from bottom to top.

Any time the distance between the clew and the head is shortened (easing the mainsheet or boom vang), twist increases. The same length of fabric is now strung between two points that are closer together, so the leech of the sail opens up. Conversely, pulling down on the clew reduces twist, closing off and rounding up the leech. A tight, round leech creates power and forces the boat to point, but it can also cause airflow to stall or overpower the boat (creating too much helm and heel). A twisted leech profile promotes airflow in light air when it’s hard to get air to stay attached. In heavy air, the flatter, more-open sections depower the sail and help keep the boat on its feet.


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