A Shark Tuning Clinic took place on May 10, 2005, at the service dock at NSC
(with Shark Poop being used to illustrate various points). It was attended by 20 or more local Shark sailors.
Johan Koppernaes (Shark Poop) gave most of the presentation, with contributions from the crowd, most notably, from David O'Sullivan (Crazy Ivan), Ron Schutte (Spam), and David Foy (Crazy Ivan).
Unless otherwise noted, the following is based on the presentation given by Johan Koppernaes
A Shark Tuning Clinic took place at NSC on May 10, 2005. |
Some general comments
When tuning a mast remember that a stiffer mast is generally better. A stiff mast has more power, it helps keep the shape of the sails. This is true when sailing aggressively (i.e. working the boat). On the other hand, a soft mast is a little more forgiving, especially for crew that sail the boat less aggressively.
When tuning the mast, it is very important that it be absolutely straight. When all the shrouds are loose, the mast is soft enough to bend slightly under its own weight.
Mast Rake
First adjustment is setting the mast rake. You do this by measuring the distance between the mast head and the sheerline of the boat at the transom. You do this with a long measuring tape (a metal tape is better because there no stretching).
Raise the tape to the top of the mast with the mainsail halyard and then pull the tape taught and measure the distance to the sheerline at the transom sheerline. Be sure to release any backstay tension. For consistency, the same person should always do the measuring with the tape. In other words, that person will always apply the same tension on the tape, and will also measure to the same spot on the sheerline. People generally accept the shackle distance of the top of the mast ( the shackle used to attach the measuring tape to the halyard).
At the clinic demonstration, the distance on Shark Poop from the top of the mast to the transom sheerline was measured at 29 feet 8 & 3/4 inches, which is about right for the desirable mast rake. Ron Schutte said he took an average of some of the faster boats in the fleet and found the measurement to be 29 feet, 9 inches.
Adjusting the Rig
Next step is to adjust the rig. Loosen all the shrouds. Center the bottom of the mast (side to side) on the mast step. Tighten the Uppers first. And the adjust the lowers to ensure that the mast is straight. The objective is to put the tip of the mast in the middle of the boat.
The tape for measuring the mast rake should still be attached to the top of the mast. Use it to measure from the top mast to the hull-deck joint next to the chainplate. Again, a steel measuring tape is preferable. Don't put too much tension on the tape because this will simply bend the mast over. Make sure to measure to the same points on both sides of the boat, and that the tape and shackle aren't jamming at the top of mast when moving from side to side. The distance on each side should be equal. In case of the demonstration at the tuning clinic, the measurement was 26 feet 4 inches on port, 26 feet 3 &1/2 inches on starboard. This is a fairly small difference. One half turn on the uppers should be enough to correct this.
Once the mast is nicely lined up in the middle of the boat, its time to tighten the uppers. Count the number of turns added to the turnbuckle on one side, and then add the same number of turns to the turnbuckle on the opposite. Johan begins by adding four turns on each turnbuckle. Says the tension on the shroud is starting to feel about right by hand. He says it is always good to get an idea of how the tension should feel by hand in case no gauge is available for make a measurement. He then uses a gauge to measure the tension of the shrouds, and it reads 200 lbs. More tension is needed for a light air setting.
Ron Schutte (Spam) says he finds settings range from about 340 to 440 pounds for light to heavy winds. Johan likes to starts at 290 pounds for a light air setting. David Foy on Crazy Ivan reports that from his experience, the extreme maximum range would probably be 240 lbs to 480 lbs.
As tension is added to the uppers, the mast becomes more compressed, so it is necessary to add a half turn on the lowers as well.
Push the lower shrouds to see what the rig will look like under load. Do so with both lowers to make sure the mast looks the same on both sides when under load. Lowers are suppose to be very soft, too soft to measure with a gauge. It should be possible to get 4 to 5 inches of total play with the lower shrouds that are adjusted for light air.
Don't pull the shrouds to just simulate load. To test tension (while sighting up the mast), push the shrouds towards the mast. This simulates the direction of the load that would develop in stronger winds.
When using open face turnbuckles, it's a good idea to have the turnbuckle for the lower and upper shrouds lined up so they can be tied together. Tying the turnbuckles together with a small line is a quick and easy way of locking-in the setting.
Shark Poop keeps the spreaders connection to the mast a little loose This is not as desirable as having rigid spreaders. Ensure that the spreaders align with the shrouds and do not deflect the shrouds fore or aft.
Adjusting for different wind conditions
It is necessary to tighten the rig for stronger winds. Start by tightening the lower shrouds to flatten the sail, and then move onto the uppers. As a very rough rule of thumb, tighten one turn on the uppers for every 3 turns added to the lowers (but this vary quite a bit among different boats, and much depends on the characteristics of each rig).
The tuning clinic was attended by 20 or more local shark sailors. |
When adjusting for different wind conditions, it's always a question of starting with a light air setting and putting on more turns. Shark Poop generally uses their light air setting for 0 to 14 km winds.
As the wind increases, the forestay can also be shortened. This reduces forestay sag, reduces helm, and automatically tightens the uppers. But changing the forestay is a big adjustment because it changes everything else. Sometimes having a fixed forestay is a blessing (and all adjustments are made with the shrouds). Shark Poop had a fixed forestay until this year, and made adjustments for various wind strengths only to the shrouds. This will be the first year Shark Poop has an adjustable forestay. But Johan believes this will be most helpful in fine tuning the rig for extremely light air.
A baseline setting
It's important to have a baseline setting for your boat. Shark Poop always maintains a baseline setting for light air. When they go out in stronger winds, they put on "turns" to tighten the rig. When they get back to the dock, they take off these "turns" to bring it back to its baseline setting. This requires discipline that you have to get used to. If you can't do this, you're lost.
Never leave the dock with an unknown setting. It's important to always be able to get back to settings that worked, that are fast for your boat under various conditions.
Some closing Comments
David O'Sullivan (Crazy Ivan) advises people to get out and try different settings to see what works for you and your style. He added that champions often go out in the same race with their boats set up in different ways. Set up your boat with what your are comfortable with, with what's suitable for you and your crew.
Johan also encourages people to write down what setting work for you under different conditions. This is particularly valuable when you feel your boat is fast vis-a-vis the rest of the fleet. After a while, you'll end up with a complete diary of all sorts of settings for a variety of conditions.
Johan added some comments about sails and sail shape. He said North sails tend to be cut flatter (he calls them footers, because not so good for pinching). Quantum sails are fuller, have more power, but maybe a little less top speed. Need power to get going, or to push through waves. Once going, flat sails are better for speed.
Set shape of the sails to be full for power at beginning of the race, then flatten sail shape for speed. If, for some reason, you have slow down and your sails are set flat , it will take a lot of time to accelerate to get up to speed again. A flat sail shape is sort of like driving a car in 5th gear. This gives you lots of top end speed on a smooth highway, but no torque to accelerate or to power through a rough road.
This article is based on the persentaion by Johan Koppernaes and written by Michael McGoldrick
(with some corrections and additions by Johan Koppernaes).
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