The tension on the upper shrouds is critical to the upwind shape of primarily the jib and to a small degree the mainsail. For maximum speed it is important to aggressively adjust the tension on the upper and lower shrouds depending on wind and sea conditions. For the uppers, which get quite tight, we use a Loos Model B tension gauge to measure shroud tension and adjust the tension depending on the wind strength using the chart below.
The lower shrouds control the side sag or bend of the mast and to a small degree how much the mast can bend forward in the middle. The lowers have a lot of control over the shape of the main because of this and it is very important to be sure they are adjusted correctly. Because the tension on the lowers is so light, we prefer to set their tension by sighting up the back side of the mast to see how much sag the mast has to set the lower tension. Note that we always will have the mast either sagged to leeward in the middle or straight. It is not fast except in extremely windy conditions to have the middle of the mast bending to windward. The chart shows the settings on the upper and lower shrouds that we have found to be fast.
|Wind Speed (Kts)||Upper Tension||Lower Sag|
|0-8 Light||Loos 12 / Loos 6 turns from base||1″ leeward sag loosen 3 turns from base|
|8-13 Lt./Medium – Base||Loos 18 / Base||1/2″ leeward sag – Base|
|13-18 Medium Heavy||Loos 24 / tighten 6 turns from base||No sag straight – tighten3 turns from base|
|18+ Heavy||Loos 30-32 tighten 12 turns from base||No sag straight – tighten 6 turns from base|
As you can see from the chart we want to get to a point where we are adjusting in full turns. The chart you build for your boat may vary slightly on the number of full turns on or off to achieve maximum performance.
After you have set up the uppers to the correct wind speed, sail the boat on both tacks checking the mast sag side to side and adjusting the lowers according to the wind speed. After you have sailed the boat a while you can create a chart of the shroud tensions and the number of turns needed to be put on or taken off the shrouds for each significant change of wind speed.
Note that in heavy seas, you will want to err a little bit on the light side (for more power) and in flat water you can err a little bit on the tight side. While class rules allow you to adjust your shrouds anytime during a race we like to set the boat up for the lightest wind speed we expect to see on the first beat. then if the wind speed changes significantly during a leg we adjust our shroud according to our chart.
Having a base setting using your light medium numbers is a good way to leave the dock each day for the races. It is easy to spin up and down from there. Develop this habit and you will find tuning the rig is not such a mystery but actually rather simple.
Mainsail: Like other boats main trim on the Melges 24 is keyed off the end of the top batten. In light to moderate air we trim the main so that the telltale on the bop batten is stalled about 25% of the time. As the wind increases the telltale will fly all the time. In light to moderate air, the back end of the top batten should be parallel to the centreline on the boat. In heavy air it will be pointed out about 5 degrees. Don’t forget that mainsheet tension is how you tension your forestay, which directly effects your pointing ability. There is a fine line on having enough tension for good pointing ability and over-trimming the main. Over-trimming of mainsails usually occurs in light air.
Jib Trim: Because the jib on the Melges 24 is a high aspect sail (tall and skinny) it is very sensitive to small adjustments in jib sheet tension. Tightening or easing the jib sheet 1/2″ can have a big effect on boatspeed and pointing. To start, position the jib lead so that the luff of the jib breaks evenly from top to bottom. Remember that if the bottom of the luff breaks first, move jib lead back. If the top breaks first move the lead forward. We have placed a telltale on the leech of the jib to help you judge how tifht or loose the sheet should be. The general rule of thumb is to trim the sheet hard enough so that the telltale is just on the edge of stalling. Just as with the mainsail it will be easy to stall the telltale in light air andvery hard to stall in heavy air even with the sheet trimmed very hard.
Jib Cloth Tension: Adjust the small line at the tack of the jib so the luff of the sail has slight wrinkles coming off it. It will be necessary to change the tension depending on the wind speed to keep a slight hint of wrinkles at all times. In very heavy air, tension the luff so that the sail is smooth.