Very Old North Sails 505 Tuning Sheet

This tuning sheet should be taken as a source reference rather than scripture. It is divided into:
  1. basic numbers by which to set up the boat;
  2. controls that are useful to acheive proper trim and sail shape; and
  3. how to use the controls.
The numbers and controls are those I have seen work and are compatible with our sails. They may or may not work for you. The important thing is to make the controls as effective and simple as possible so that you spend a minimum amount of time adjusting and a maximum amount sailing. Hike back, sheet in, and enjoy!


These are approximate. Adjust until you have a balanced helm sailing hard upwind with the boat absolutely flat. The rig should be very tight in all but drifters.
Mast Rake
25' 8""
Attach tape measure to halyard shackle; raise to top of mast; run tape through transom flap; measure to hull/transom intersect. Jib must be raised with rig tensioned as for sailing.
Centerboard Pin
8' 4" to 8' 6" from transom.
Mast Step
Fore and aft track mounted 12" above the floor at about 7' to 8' 6" forward of transom. We find a sprong-pin slider for the lead blcok perfectly adequate. Move it forward to increase leech tension, aft to open the leech. alibration tapes for duplicating fast positions are essential.
Spinnaker Lead
30" forward of transom."
Measurements taken from deck-level black band.
Side Stays
Our shroud pin is at 16" 7" which is level with the spinnaker halyard. Some people have it at jib halyard height for maximum rig tension or lower to restrict bend.
Trapeze Wires
16' 7". ours hang on the same pin as the shrouds. raise them to" stiffen the tip; lower them to induce tip deflection to leeward, spilling power.
10'. They should be cut and pinned to deflect the shrouds about 1 1/2" " outboard to restrict fore and aft band.
Pole Lift Sheave
10' 11" for our lift system."
Pole Ring
3' 6"."


The centerhorse, the bridle, and end-boom sheeting are the three common systems. They have almost entirely replaced the traveller. All rely on a very strong vang and a stiff boom. The vang controls main leech tension which reduces the forces on the main sheet. All the sheet does is move the boom in and out. Reduced forces allow you to play the sheet more (fast!) with fewer parts (less line to pull in and weight the boat down) without getting exhausted (well, only a little).
Strong lever with 4 parts purchase. All fittings must be very strong: gooseneck, boom bail, mat bail. Drill holes on the neutral axis of boom and mast. Run shock cord from the lever to the gooseneck to keep the lever in line.
Cumulative purchase on a lever vang varies with the angle of deflection of the lever. It is important to keep the standing part tight for maximum power. An adjustment on the standing part is required from light to heavy air. With any of the above mainsheet systems the vang is very important. It should be led out to either rail for constant adjustment.
The lens foot main is very responsive to outhaul tension. Outhaul adjustment should be quick and easy for major changes in wind strength and/or sea conditions.
Mast Ram:
The best way to control the lower mast; it either restricts or induces bend. Controls may be led aft with enough purchase.
Pole Lift/Stowage:
The height of the lift exit sheave on the mast is critical: the lift is the same length when the pole is stowed on the boom and when it is up. There are no fittings to hold the pole on the boom. It is held up only by the shock cord to boom and downhaul and the pole list.

The pole must be retracted before the jibe, the reset on the new jib. DANGER: Trim boom when stowing the pole to leeward to avoid hooking leeward shroud with pole. INSTANT CAPSIZE!
Twing Lines:
Excellent replacement for reaching hooks: faster and safer. Twing is continuous to both sides of boat. Release one, trim the other from either side of boat. Release one, trim the other from either side of the boat. Trim both twings and cleat both sheets through heavy air jibes.


Most of these controls must be used interactively. The setting of one is dependant on several others. What you are trying to achieve is main and jib shapes that are fast foils in any conditions and that work well together. In light air you will want the main to be flattened (outhaul trimmed and mast pre-bent) and trimmed in close (mainsheet) with an open leech (slack vang); in moderate air, it must be deep (eased outhaul/rammed mast) and powerful (leech tightened with vang). In heavy air, the sail must be flattened again (outhaul trimmed tight and mast pre-bent) with the upper leech opened (cunningham on hard and vang eased) enough to allow the sail to be played continuously through puffs and waves to keep the boat flat and driving off on an upwind plane. Jib shape is achieved primarily through sheet tension adjustment; the lead is not changed much except in very heavy air (move 3" aft)." Trim the sheet in tight for pointing once the boat is moving. There should be just a hint of backwind in the main. Ease in chop to open the slot.

Good Sailing