North Sails Tuning Guide

Proper boat speed depends mostly on constant and consistent adjustments to your rig and sails. The following measurements are those that we have found to be the fastest settings for your new North sails. We have brushed and tested different tuning settings to be sure that we have the fastest and easiest measurements available. If you have any questions or problems with you speed or sails, please don’t hesitate to call.

MAST BUTT PLACEMENT: The back edge of the stock butt plate should be 111″ from the inside of the transom when measured along the floor of the boat The back edge of the mast, when sitting on the forward pin in the step, should be 114″ from the transom.

MASTRAKE: To measure your mast rake, hoist a metal tape measure on your main halyard, lock it, and hold the tape tight at the top of the transom in the middle of the transom. The measurement is always taken with the jib up, and with all the load on the jib halyard and luff wire. This measurement should be 23′ 5 1/2″ – 23′ 6 1/2″

RIG TENSION AND SHROUD PLACEMENT: we suggest setting your shrouds so that the rig will be tight enough that the leeward shroud will not go slack sailing upwind until the wind is blowing approximately 10 mph.

An excellent method to determine a more precise tension is to use a small Loos tension gauge on the shrouds. The reading with this smaller tension gauge will be 18.

SPREADER LENGTH AND CANT: Your spreaders (with the standard mast) should be 17 1/2″ long, with a 7″ – 9″ cant (see diagram). Spreader cant will be determined by your crew weight. Heavier crews will sail with shorter numbers (spreader tips farther apart).

MAST PREBEND: With the proper rake, rig tension, and spreader set your mast should develop approximately 1/2″ of positive prebend when…sighted up the back of the mast.

MAST BLOCK: At this point, the mast should be blocked at the deck in order to limit mastbend. This will insure that the mast will not overbend and overflatten the mainsail in heavy winds.

NOTE: It is suggested to remove this block downwind to avoid any undue strains on the mast at deck level.

MAIN CUNNINGHAM AND JIB CLOTH: For both the main and jib, never apply more luff tension than is necessary to just barely remove the wrinkles. Most times it is actually better to leave a hint of horizontal wrinkles in the lower 1/4 of the luff of your main and jib to be sure you haven’t pulled too tight.

JIB LEAD TRIMLINE: Your North jib is built with a “trimline” penciled in from the clew grommet out towards the body of the sail. This is the most accurate check in determining proper jib lead position. When the jib lead is position properly, your jib sheet should appear as an exact extension of this trimline. At this point both telltales, top and bottom, should break evenly as the boat is luffed into the wind.

In heavy winds, when the boat is overpowered, move your jib leads aft as much as 2″ at which point your jib sheet will angle slightly aft of the trimline and your jib will become flatter up top with the leech more open.

JIB SHEET TRIM: unfortunately, there is no easy guide for trimming the jib sheet. We are looking for a parallel slot between the exit of the jib and the entry of the main. The guide which has been very successful is that of imagining a middle batten on the jib at mid-leech. This “batten” should be set parallel to the centerline of the boat which will make the upper half of the jib leech twist outboard slightly, and the lower half twist inboard slightly.

It is important to be careful not to overtrim the jib and hook the imaginary batten tighter than parallel with the centerline of the boat. It seems that 90% of the boat speed problems experienced are due to faulty jib sheet trim.

MAINSHEET TRIM: Trim the main through use of the mainsheet and the boomvang so that the last 1/3 of the upper batten is parallel to the boom (sighted from under the boom, looking up the sail). In light winds it will be impossible to keep the upper batten hooking from hooking slightly to windward due to the large roach of the C15 main. In these conditions set the upper batten parallel to the centerline of the boat (instead of parallel to the boom). This will position the boom farther off centerline which is acceptable since in light winds the boat is driven much harder and not pointed near as much as it is in medium and heavy winds.

In heavy winds, maximum mast bend will open the upper leech so that the upper batten will be angled 5 to 10 degrees out from parallel to the boom.

BOOMVANG: Downwind we trim the vang just enough to keep the boom down and the leech “set” on the mainsail (the back 1/3 of the upper batten parallel to the boom).

Upwind it has become popular to use the vang to keep the upper batten parallel and force more bend into the mast. In puffs, when the mainsheet must be eased out quickly to help balance the boat, easing the mainsheet in a puff would actually allow the mast to straighten up, causing the sail to become fuller. In effect, keeping the vang set tight upwind in a breeze will actually set the tension down on the boom, allowing the mainsheet to control the angle of the boom to the centerline.

TRAVELLER: The traveller is used to further depower the main. The skipper should be able to easily reach the traveller controls while hiking. This way, when a puff hits, it easy to drop the traveller to leeward to keep the helm and boat balanced. When the wind lightens, the traveller must come back up. In very light winds, pull the traveller to windward to help keep the boom closer to centerline and still maintain the aft 1/3 of the upper batten parallel to the boom. Be sure to pull it up to windward as quickly after a tack as possible and not leave it to leeward for any length of time.

Boom end sheeting with a bridle traveller is becoming more popular in the C-15 class. The height of the bridle should be determined by the mainsheet almost being able to “two-block” in a medium (12 to 15) mph wind. If your bridle and mainsheet blocks touch before proper mainsheet tension has been applied, the boat will not develop top speed or pointing capabilities.

Many C-15 sailors are now using a “split mainsheet” boom end system which makes trimming the mainsheet much easier. Basically a purchase is reduced at the end of the boom so that the traveller bridle legs can be sewn into the mainsheet where it enters the boom end block. Call us if we can help you set this up.

OUTHAUL: Pull the outhaul to the band except in very light or choppy conditions when extra power is desired. In these conditions it is advantageous to ease the outhaul 1″ to 2″. When the outhaul is pulled out tight you will notice the beginning of a crease just above the boom. This crease is normal as it is the extra fullness built into the sail for power when the outhaul is eased.

North C-15 sails have been designed to be fast and easy to adjust. If you have any questions or problems please don’t hesitate to give us a call.


1111 Anchorage Ln.

San Diego, CA 92106

(619) 226-1415

Fax (619) 224-7018

Chris Snow


Columbus, OH 43215 (614) 221-2410

Fax (614) 221-1228

Greg Fisher