Very Old North Sails 505 Tuning Sheet
This tuning sheet should be taken as a source reference rather than
scripture. It is divided into:
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!
- basic numbers by which to set up the boat;
- controls that are useful to acheive proper trim and sail shape; and
- how to use the controls.
I. BASIC NUMBERS:
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
- Spinnaker Lead
- 30" forward of transom."
- MAST RIGGING
- 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
- 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"."
II. THE CONTROLS
- 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).
- Centerhorse: One of its nicer aspects is that it gives you a handle to
grab in a roll tack. It is somewhat heavier than the bridle, but is rigid,
- Bridle: The block at the top of the centerhorse is held in position by two lines
led from each side of the cockpit.
- End-boom sheeting: The boom can be centered in light air, but it is tricker
to tack the tiller extension and it is harder to grab all the parts of the
mainsheet for one-to-one purchase downwind. Also for use with strong vang
and stiff boom. Sheet always pulls from weather rail. Splice meets end of boom
with boom centered at its highest level, vang released.
- 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
- 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.
III HOW TO USE THEM
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.