North Sails RESOURCES
Interlake Tuning Guide
- Last Updated: August 23, 2017
- Tuning Guide (PDF)
Congratulations on your purchase of North Interlake sails. We are confident that you will find superior speed over all conditions. Time has been spent to insure that not only are your sails fast, but also easy to trim. Please read the following guide, set up your boat to the numbers specified, and go racing! If you have any questions or problems, please don’t hesitate to give us a call. We are anxious to help you go faster and win races.
BASIC RIG SETUP
MAST BUTT PLACEMENT AT DECK
Maximum forward – 6’4” (76”) from the stem to the forward edge of the mast. Remember that the measurement is from the imaginary intersection of the hull and deck. Do not include the rub rail.
Measure mast rake by hoisting a tape measure on the main halyard and latch it where the halyard would be at the top black band. Pull the tape back to the middle of the transom at the joint between the transom and the deck. The measurement at this point should be 25’3”.
Keep in mind that you will measure your rake measurement when the rig is tensioned, whether it is by jib halyard tension or by tensioning the forestay itself
We have found that the Interlake performs best when the rig is set up fairly tight.
There are several different methods Interlake sailors use to set up and tension their rigs when sailing. Some set the forestay very tight and adjust the halyard tension to set the cloth/luff tension. Some set the forestay only snug and then add more tension through adjustment to the jib halyard (which will make the forestay actually become slack as all the tension is taken on the luff wire in the jib) with a powerful block and tackle arrangement.
In either case, ideally the tension will be tight enough that the leeward shroud would just become slack when sailing upwind in a 10 mph breeze.
For those who like to check the rig tension more precisely with a Loos tension gauge, we suggest the tension be set so that the shrouds register around 250lbs In lighter breeze ( below 8mph) ideally the tension will fall between 200 and 250lbs. For breeze over 12 the proper tension will be increased to nearly 340lbs.
Your centerboard should never swing farther forward then straight down (leading edge vertical) or perpendicular to the hull when it is lowered to its maximum. If your board swings past vertical, tie a knot in the centerboard pennant to limit its travel.
Some Interlake sailors have had success in heavier winds raising the board slightly in order to help maintain a balanced helm.
JIB LEAD PLACEMENT
Your Interlake jib has a trim line drawn from the clew grommet towards the body of the sail. This line provides the most accurate check for your basic jib lead position (below12 mph winds). Your jib leads should be positioned so that the sheet is a direct extension of this trim line. This is more effective than a measure from the stem because of variations in jib lead fittings, deck styles and small rake differences.
In heavy winds (above 12 mph), move the leads aft 1- 1 1/2 inches from the basic trim line position.
JIB CLOTH TENSION
Setting the cloth tension along the luff of your North jib properly is important in setting up the designed shape. Again there are several different methods used by Interlake sailors the cloth tension.
The “adjustable luff” system means your boat is equipped with an adjustable jib tack/Cunningham. Shackle the luff wire to the bow plate and attach the jib cloth shackle to the grommet in the sail. The tension is usually adjustable back in the cockpit.
The “furler luff” jib is fitted with a small clam cleat near the tack that allows the tension on the cloth to be adjusted independently of the luff wire tension.
Like the adjustable luff jib, the halyard is attached to the luff wire at the head of the jib and usually tensions the rig.
The “Burkhardt luff” system actually has two halyards, one for tensioning the rig (and attaches to the luff wire) and one for adjusting the cloth tension ( and attaches to the grommet in the cloth at the head). This system is used primarily with a jib furler.
In all three systems, adjust the cloth tension just tight enough to barely leave the horizontal wrinkles along the luff that appear as “crows feet” at each snap. In winds above 10-12mph, tension the cloth so that the luff is just smooth and no wrinkles or crows feet are present.
Trim the jib sheet so that in “boat speed” conditions the middle batten is straight aft parallel with the centerline of the boat. In light wind and/or sloppy conditions, ease the jib sheet so the middle batten is angled outboard 10 degrees. Also in breezy conditions, ease the sheet for more twist in the leech.
Only in medium winds and relatively flat water will the jib ever be trimmed so that the middle batten is just slightly hooked to windward and the top batten nearly straight back…and for only short periods of time.
Included with your new North mainsail are special tapered battens specifically chosen to perform best with your sail. When inserting the tapered batten, the thinnest end of the batten should be inserted first for the greatest flexibility on the inboard end.
Pull the outhaul tight enough to just induce a slight horizontal wrinkle along the foot. In heavy winds or when the boat is overpowered, tension the outhaul until you will notice a horizontal crease along the foot.
Downwind, ease the outhaul only until the foot is smooth…never to the point of vertical wrinkles off the foot.
Your North mainsail is built with a maximum length luff. As a result, cunningham tension is used to tighten the luff of the mainsail and position the draft (maximum depth) properly ( nearly 45- 50% aft) in the sail.
In light winds (less than 6 mph) there should be small wrinkles perpendicular to the luff all the way from the head to the tack.
In medium winds there should be horizontal wrinkles only in the lower 1/3 to 1/4 on the mainsail.
In heavier winds, tension the Cunningham until the luff is nearly smooth.
MAIN SHEET TRIM
The main should be trimmed so that the upper batten is parallel to the boom (sighted from under the boom looking up the sail).
In lighter winds, or when sailing in a great deal of chop, it is helpful to ease the mainsheet slightly so the upper batten is angled out approximately 10-15º.
In drifting conditions, when the boom is hanging on the leech and hooking the upper batten, set the upper batten parallel to centerline of the boat. Only in drifting conditions should the main be trimmed this way, as this will place the boom approximately 2′ (61 cm) off from centerline.
In very heavy winds ( above 12mph), with the help of the boom vang, set the mainsheet tension so the upper batten is again angled outboard approximately 5º from parallel to the boom. It is important, in winds above 15 mph, to apply heavy boom vang tension so the mast and boom will bend correctly to sufficiently flatten the sail. It has been found that the boom may be deflected from the straight line nearly 3” in heavy breezes. This heavy boom vang tension will help make playing the main much easier, as the sheet will not have quite as much strain as it does in even moderate winds.
Note: Make sure when rounding the windward mark that the boom vang is eased to your normal downwind trim so more strain is not applied to the mast and boom!
The boom vang is used downwind to keep the upper batten parallel to the boom. A sailcloth telltale is attached to your mainsail leech at the upper batten. This telltale is used to help determine the proper boom vang tension (and therefore mainsail twist) on reaches or runs. Too much or too little vang will stall this telltale and will indicate that vang adjustment is necessary.
Note: We suggest not using this telltale to determine mainsheet trim upwind as proper trim upwind will result in the telltale showing a stall 50-75% of the time.)
Upwind, as indicated above, the vang is used in heavy winds to help maintain the upper batten parallel to the boom. If the vang is properly adjusted, when the mainsheet is eased in a puff, the boom moves outboard laterally. When tensioned properly in bigger breeze, there will be as much as 3” of bend in the boom.
The traveler is used to depower and balance the boat by easing the mainsail sideways in heavy winds. When heavy windward helm develops ( the boat wants to turn up into the wind) the traveler is eased to help keep the boat flat. The traveler bridle height should be 24” from deck level to the top of the block, or as high as possible to allow centering the boom in light winds while still allowing enough mainsheet tension to adjust
the leech tension in moderate to heavy breezes. If your bridle height is adjustable, set the height at 28” in light winds and as low as 18-20” in very heavy winds. Be absolutely certain that the traveler height is set so that you will never run out of distance between the traveler blocks on the bridle and the mainsheet block (“two block”). Running out of mainsheet trim before the upper batten becomes parallel with the boom will greatly hinder your Interlake’s ability to point.
Keep the two clews of the spinnaker even with the deck by adjusting your pole height with the topping lift. The halyard should be lowered so that the spinnaker flies 8 inches off the mast and away from the mainsail. Start with the spinnaker pole positioned perpendicular to the apparent wind direction as indicated by the masthead wind indicator. Try to always carry 6-12 inches of curl in your spinnaker luff. No curl means the spinnaker is over trimmed. The crew and the helmsman must work together closely when sailing in heavy winds with the chute. The crew must ease sometimes as much as 3 feet to allow the skipper to bear off in a puff to keep the boat flat. The skipper must always be prepared to ease the mainsail downwind to keep the boat flat and balance the helm.
The only exception to keeping the boat flat is when sailing directly downwind. Under these conditions, balance the helm and allow the spinnaker to swing out behind the mainsail by heeling the boat to windward. Pull the centerboard up as far as possible; only leave enough board down to allow the boat to answer the helm without crabbing sideways or to prevent excessive rolling. If rolling occurs, lower the centerboard at least halfway IMMEDIATELY to prevent the infamous “death roll” to windward, and then pull it back up when the rolling ceases.
OTHER IMPORTANT ITEMS
We suggest sailing with a combined crew weight of 390-460 lbs. Keep the boat almost perfectly flat upwind (except in very light wind) and place the crew weight as far forward as possible. Keep the crew and skipper close together and line up directly behind the shroud when there is enough wind to have all three on the weather rail. The only exception is when sailing in waves where the crew all move back one foot to allow the bow to ride up and over waves more easily.
Rapid tiller movement seems to slow the Interlake. Instead, slow, gradual movements are best when sailing upwind. Tacking is quickest when actually steered through slowly. Keep the boat moving.
ROLLING THE SAILS
Leave the battens in the mainsail. Start at the head of the sail and roll the sail parallel to the seams (which are parallel with the battens so they won’t get twisted). Put the luff end of the sail into the tube bag first. If the jib sheets remain attached, they can be left out of the tube to dry if they are wet.