Interclub Tuning Guide

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INTERCLUB TUNING GUIDE - SB (BENJ) DESIGN

The following measurements are taken with the 0 (reference) point of the tape measure at the exact center of the transom at deck level. This is the point known as T1 in the IC Dinghy Rules. If there is a lip extending aft or rail in this place determine the intersection of the transom, centerline, and deck planes and use this as the reference point. This point is exactly 1' 6" above the transom's intersection with the bottom. The last three measurements are taken with the tape sloping downward.

Aft opening of mast partners: 8' 11"
Front opening of mast partners: 9' 2 5/8"
Aft side of mast at step: 9' 2 5/8"
Front of mast at step: 9' 5 3/8"
Center of centerboard pivot: 6' 7"

The mast should be adjustable with chocks at the partners. With the above step location and the correct rake you will need all the chocks in front of the mast at the partners to restrict mast bend in most conditions. In very light air experiment with prebend (chocks aft) to determine performance benefits.

The mast step should be positioned as measured above so that rig can be controlled properly and to insure the correct mast to sail match. As a check the dimension from the centerboard pivot to the aft side of the mast at the step is 2' 9 3/4."

The chainplates should be located at the maximum forward location. There are several different rules which control and are currently being clarified. You may locate the chainplates anywhere aft of 1.5 inches behind the maximum aft location of the mast partner, or check for the latest interpretation. A diagonal measurement from T1 of 8' 11 1/2" will be about right.

To set the mast rake fix the main halyard in the locked position (as though the sail were fully hoisted) and with the tape affixed to the shackle measure to the T1 point at the center of the transom (deck) 18' 8 1/2". The headstay should be completely slack and the mast should be resting against the aft opening of the partner with no blocks. The shrouds should be quite firm (approximately 200 pounds measured on a small tension gauge) (See Tension Gauge Conversion Chart) to keep the rig stable. Be sure the mast is central and the sail track is dead straight side to side - if it is not adjust the shrouds to make it so. Two people are needed to fix the shrouds in their chainplates, or you can create the necessary slack in a side shroud by fixing the main halyard to the outhaul and sheeting on the mainsheet (with the traveller to the side you are working on). Having said this we have seen excellent boatspeed offwind in light air by using slack shrouds which allow the rig to pull forward offwind. With the ’97 Standard main more experimentation with loose rigs is required since there is no longer a need for tight shrouds and prebend.

The headstay is an important power adjustment. After setting the rake as above, pull the headstay on tight enough to measure 18’ 9.5”, and add enough blocks behind the mast to make it dead straight fore and aft (no prebend). This is your base setting for medium winds. The tighter the headstay is pulled, the fuller the sail gets. The fuller sail is better for boatspeed and waves, while the flatter sail is better for pointing and flat water. One technique is to tie three overhand knots in the headstay line. These provide certain reference points, and most of the time you should be on the middle knot. You will need a fairly firm forestay to control the Zephyr mast and it should be tight to the feel at rest for medium to strong winds and just slack in light winds (use more headstay tension as the wind increases to control mast bend).

The outhaul should be normally kept so the distance from the side of the boom to the sail is less than one full hand spread (tip of thumb to tip of pinky = 8 1/4"). Experiment with the outhaul even tighter for flat water and heavy air, and looser for chop. Always ease for offwind.

The vang is never pulled on until you are overpowered upwind. At all other times it should be not quite firm so the boom does not rise while tacking. Offwind we are finding better speed with a surprisingly loose vang and open upper leech, but be careful of sailing with the vang too loose in heavy air (a good way to capsize). The ’98 Standard requires a tighter vang to control the sail’s tendency to twist open out of a tack.

The traveller should be approximately 7" from the corner to assist in pointing and allow the sail to be trimmed without too much main sheet tension (which would close the leech). The exception is in heavy air with the Zephyr mast when the traveller should be allowed to go fully to leeward.

Upwind technique in heavy air depends on the mast. The Zephyr is much bendier than the Kenyon, and requires less vang with the traveller all the way to leeward. The Kenyon can handle heavy vanging and the traveller can be kept 7" from the corners (since you are vang sheeting and easing the mainsheet to depower as needed).

The centerboard should be marked with the front edge vertical. In smooth water and when the boat is sailing well the forward tip can be about 4" forward of this location to improve pointing. Raking the board forward makes the boat stall more easily, so be careful of this technique.

North Sails will be pleased to discuss your individual questions and experiences. Please consult us for the latest in Interclub sail development.

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