GENOA TRIM: How to Optimize Power and Pointing
3/19/2008
Use these rules of thumb for genoa trim as a starting point, then experiment with small changes to see what works best for your boat.
WIND RANGES
It is important to always follow the recommended wind range for your genoa. Using the sail in too much wind will not only slow your boatspeed, but also can damage or stretch the sail. If you are unsure what the wind range is for a particular sail, contact your Ullman Sails loft.
SHEET TRIM
When trimming the genoa, the most important adjustment is sheet tension. Spend some time looking up and learning the relationship between the spreader tip and the sail. In choppier water and/or light air, ease the sheet slightly to give the genoa more leech twist. In flatter water when the boat has enough power, less leech twist will help increase the boat’s pointing ability.
Keep your eyes open – watching the knotmeter and other boats around you will help determine how tight to sheet. It is also helpful to put a telltale on the upper leech to monitor stalling. If the telltale isn’t flowing, ease the sheet. After tacking, the sheet should be trimmed short of full tension until the boat is up to full speed. In puffy wind, a trimmer should stand by the sheet to adjust it as the wind changes. Finally, communication between the helmsman and the trimmer is key to getting speed out of the boat.
LEAD POSITION
FORE & AFT
The genoa lead controls the fullness in the bottom third of the sail. It can be thought of as the outhaul for the genoa. To determine what your “powered up” setting is for a specific genoa, set the lead and trim in. Head the boat up and watch to see where the luff backwinds first.
The genoa lead controls the fullness in the bottom third of the sail. It can be thought of as the outhaul for the genoa. To determine what your “powered up” setting is for a specific genoa, set the lead and trim in. Head the boat up, watching to see if the luff of the sail breaks evenly. If it breaks up high first, the lead is positioned too far aft. If it first breaks low on the luff, the lead is positioned too far forward. The goal is for the luff to break evenly. The foot should be full and almost lay against the lifeline.
When the boat requires more power in choppy water or lighter wind, adjust the lead further forward. And as the wind increases, the lead should be moved aft to flatten the foot and depower the top of the sail by allowing it to backwind first. With a #1 genoa, the fore and aft adjustment can be as much as a 1 foot. At the top of its wind range, the genoa should be trimmed with the foot flat against the shrouds.
INBOARD & OUTBOARD
The in and out placement of the lead is adjusted less often than fore and aft. The track placement on the deck usually determines the innermost lead position. However, some boats have an inhaul that will allow you to sheet further inboard than the track with non-overlapping jibs.
Most modern racing boats sheet the #1 genoa at 7 degrees outboard of the track in light to moderate breeze. To extend the upper range of any jib, you can sheet further outboard by using a short sheet that runs through to a second track or the toe rail.
A #2 genoa is limited by the shrouds and has a shorter LP, therefore is sheeted about 10 degrees outboard of center. A #3 genoa can be trimmed in front of the spreaders, so the lead can be as close as 7 degrees outboard of center in flat water to allow very high pointing.
Overall, the fore and aft lead movement is more critical than in/outboard adjustments. And the in/out range is smaller – only 3 to 4 inches. Anytime you are reaching, the lead should go outboard. When the apparent wind moves aft of about 35 degrees, the lead should go to the rail and further forward. Remember: the rule of thumb is to keep the luff breaking evenly.
HEADSTAY SAG
While the lead controls the fullness in the bottom of the genoa, headstay sag controls fullness in the middle and top of the sail. More sag adds fullness, moves the draft slightly forward and makes the entry rounder. When you boat needs more power, some headstay sag can be beneficial. This is typically the case for a light #1 genoa or higher. But it is important to remember that if you get caught with a sail in wind below its range, sag will help power it up. Also, be careful not to use so much sag that the headstay bounces in choppy water.
As the wind increases nearing the upper range of your genoa, you should remove as much sag as possible to flatten the sail. How you do this depends on your type of rig. If you have a masthead rig, backstay tension controls sag. Remember that over-bending the mast can contribute to sag! This may happen if you have a flexible mast and don’t use enough running backstay. In general, the backstay should be well eased in light air (as low as 500 lbs.). Tension the backstay as the wind increases. The maximum backstay tension varies from boat to boat. On a typical 40-foot boat, it can be as high as 5,000 lbs. A typical 30-foot boat would use about 3,000 lbs.
On a fractional rig, the running backstay controls sag and this adjustment becomes particularly critical in puffy wind. Small changes in runner tension greatly affect headstay sag, so assign a crew member this job. As the wind drops, the runner should be eased. As the wind increases, increase runner tension.
HALYARD TENSION
Halyard tension controls the fore and aft position of the draft – the maximum fullness of the sail. The draft should be about 40% aft of the luff. In underpowered conditions (usually with the light or all-purpose #1 genoa), a good rule of thumb is to leave some small horizontal wrinkles along the luff. As the boat gets powered up (10-12 mph of apparent wind), barely remove the wrinkles. In stronger breeze with a heavy #1, #2 or #3, increase the halyard tension. This will hold the draft forward and make the head slightly fuller. Choppy water requires the draft to be further forward and the entry rounder. This makes the boat easier to steer. In flatter water, the entry can be finer, so allow the draft to slide aft to improve pointing. Always be careful not to use too much halyard, especially in puffy wind. Too much luff tension is slow in light air.
If you have any questions about your Ullman genoa that are not answered here, please contact your Ullman loft.